Science Focus 3 4ia23

Nitrates used by plants

7.2

UNIT

7.2

De-nitrifying bacteria in soil convert nitrates into atmospheric nitrogen.

[ Questions ]

Checkpoint Two types of matter 1 Identify the two groups into which we classify all matter. 2 List two examples of each type of matter you identified in Question 1. 3 a Define the ‘biotic’ and ‘abiotic’.

b Classify each of the following as a biotic or abiotic feature of the environment: water, leaf, soil, air, algae, bacteria, rock, grass, cloud, human.

The water cycle 4 Describe the water cycle. 5 Define the following : a condensation

b evaporation

c precipitation

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Recycling in nature

The carbon cycle 6 Draw a diagram to illustrate the basic conversions that occur in the carbon cycle. 7 Identify where, and in what form, carbon enters a plant. 8 a Identify the process whereby plants convert carbon dioxide and water into the sugar known as glucose. b Identify the source of the energy for the above process. 9 a Identify an important gaseous product of the process described in Question 8. b Explain why this by-product is important.

[ Extension ] Investigate 1 Research the phosphorous cycle and the effect that fertilisers have on the environment. Include a diagram in a short written report of your findings. 2 Investigate how coal is formed. Explain how the carbon in coal is eventually released back into the environment. Illustrate your short report with a ‘carbon-cycle’ that shows the important conversions.

The nitrogen cycle 10 Is nitrogen, N2, an organic or inorganic compound? Justify your answer. 11 Draw a diagram to illustrate the main conversions that occur in the nitrogen cycle. 12 Identify two acids in the human body that require nitrogen. Explain why these acids are important. 13 State the form in which nitrogen exists in: a the atmosphere b the soil c urine and faeces

Think 14 Deduce whether the following statements are true or false: a Nitrogen and carbon atoms move between the abiotic environment and the biotic environment. b Most living organisms need water. c The nitrogen cycle, the carbon cycle and the water cycle all the Law of Conservation of Matter. d Bacteria play an essential role in the continuation of life. 15 Describe what lightning does in the nitrogen cycle. 16 List three different bacteria that can fix nitrogen.

Create 3 Imagine that you are a carbon atom. Describe what you have been doing for the past 100 years. What interesting things have you been a part of, and where do you think you will go next? Construct a diagram of your life cycle so far. 4 a Use an old fish tank or large glass jar to construct a terrarium to simulate the DYO water cycle. b Place labels on the outside of the tank to explain what is occurring in each part of the tank in relation to the water cycle. 5 Use a computer program such as Flash to construct an animation of the carbon, nitrogen or water cycle.

Surf 6 Explore the informative and interactive animations of the carbon and water cycles by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7 and clicking on the destinations button.

17 Distinguish between the different types of bacteria involved in the nitrogen cycle.

Analyse 18 What would happen if all the decomposers on the Earth suddenly disappeared? Explain your reasoning.

UNIT

7.2 202

[ Practical activities ] Testing for water Aim To test for the presence of water in

Prac 1 Unit 7.2

different liquids

Equipment Cobalt chloride paper, anhydrous copper(II) sulfate, watchglass, pipette, paper towels, various liquids (tap water, methylated spirits, salt water, sucrose solution, acetic acid (2M)), unknown liquids X, Y and Z

Measuring the boiling point of water

Method There are two simple tests that determine whether a liquid contains water. • Test 1: When water is added to anhydrous cobalt(II) chloride paper, it turns the paper from blue to pink. • Test 2: When water is added to anhydrous copper(II) sulfate, it turns from white to blue. Note: The term ‘anhydrous’ means ‘without water’. 1 Drop a small amount of water on a small piece of anhydrous cobalt(II) chloride paper and a small sample of anhydrous copper(II) sulfate. that each changes colour according to test 1 and test 2 listed above. 2 Copy the table below into your notebooks.

Prac 2 Unit 7.2

UNIT

7.2 Aim To measure the boiling point of various samples of salt water

Equipment Bunsen burner and mat, tripod, matches, tongs, four 250 mL beakers, distilled water, salt, tablespoon, thermometer able to record temperatures higher than 100°C

Method 1 Copy the table below into your notebook. Liquid

Boiling temperature

Beaker 1 (distilled water)

Liquid tested

Copper(II) sulfate

Cobalt chloride paper

Beaker 2 (1 tablespoon salt) Beaker 3 (2 tablespoons salt)

Tap water Beaker 4 (3 tablespoons salt) Methylated spirits Salt water Sucrose solution Acetic acid Unknown X Unknown Y Unknown Z

3 Place one spatula of anhydrous copper(II) sulfate on a watch-glass. 4 Add 5–10 drops of tap water and record any colour change. Record your results. 5 Wash and dry the watch-glass thoroughly. 6 Place a piece of cobalt(II) chloride paper on the cleaned watch-glass.

2 Set up the Bunsen burner, the mat and the tripod. Light the burner. 3 Label the beakers 1 to 4. Add 200 mL of distilled water to each. 4 Heat the water in beaker 1 until it boils. Measure the temperature and record the result. (Note: Place the thermometer in the water while it is still cold and heat it gradually. Allow it to cool down a little between tests.) 5 Using tongs, remove beaker 1 and place it to one side. 6 Place beaker 2 on the tripod. Add 1 tablespoon of salt and stir until the salt has dissolved. Continue heating until the water boils. Measure the temperature and record the result. 7 Using tongs, remove beaker 2 and place it to one side.

7 Add one drop of tap water and record any colour change. Again, wash and dry the watch-glass thoroughly.

8 Repeat steps 6 and 7 with beakers 3 and 4.

8 Repeat steps 3–7, replacing the tap water with each of the solutions listed above.

Questions

9 Record your results.

Questions 1 Apart from a colour change, describe what else happens when water is added to anhydrous copper(II) sulfate.

1 Construct a line graph to show the relationship between the amount of salt dissolved in water (on the horizontal axis) and the temperature at which the water boiled (vertical axis). 2 Propose a reason for the results you observed.

3 Identify which of the unknown liquids contained water.

3 Antifreeze is a salty solution that is often put in car radiators to stop the water from freezing in very cold weather. It is also very useful in stopping radiators from boiling in hot weather. Analyse why.

4 Assess the importance of washing and drying the watchglass thoroughly between each test.

4 Analyse this statement: ‘Impurities in water increase its boiling point’.

2 Identify which of the known liquids contained some water.

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UNIT

context

7. 3 Individual humans have similar energy requirements to other mammals of comparable size. As a population, however, we have developed enormous energy requirements. In many countries, people have come to rely on all kinds of luxuries. Although inventions such as televisions, cars and air conditioners make our lives more pleasant, they are not really essential to life. A lot of energy is used in producing and running them. It is these non-essentials that have caused an energy crisis and an imbalance in the

Earth’s ecology. The future of the human race will be determined by what we do about our production and use of energy.

Energy sources are classified as non-renewable or renewable.

coal flue gas cooling water steam reheat air condensate

to station switchyard

detail of separation firing vapour burner feed water

economiser

steam from reheater steam to reheater

degenerator

reheater super heater

steam from super heater

coal bunker boiler

separator

turbo generator

chimney

burners rotary air heater air

precipitator boiler feed pump

circulating water pump

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coal conveyor from open cut

gas

natural draught cooling tower

Fig 7.3.1

main burner

condensate pump

LP HP heater heater

pulveriser

water from separator

air intake FD fan

air supply duct

ID fan

ash removal to ash settling pond

Coal power stations pollute when they are operational. Their waste products are often toxic and environmentally destructive.

Non-renewable energy sources Energy sources that cannot be replaced are referred to as non-renewable. These energy sources include: • fossil fuels such as coal, gas, crude oil and its products petrol, diesel, kerosene and aviation fuel • uranium and other nuclear fuels used in nuclear power plants.

UNIT

7.3 There’s a dinosaur in my car! Fossil fuels are really just prehistoric plants, animals and algae that died millions of years ago. So when the family car is next filled, it is very possible that some dinosaur is being pumped in!

Fossil fuels Fossil fuels form when dead organic matter is not decomposed. This most often occurs in bogs and swamps. Oxygen is scarce in the mud at the bottom, making it impossible for decomposers to break down dead matter that has fallen there. More mud and silt slowly deposits on top, until the dead matter is eventually covered with dirt. Intense pressure and heat from movement in the surrounding earth over millions of years compresses and ‘cooks’ the matter first into coal, and then into crude oil and gas. While the burning of these fossil fuels provides large amounts of energy, it also releases large quantities of pollutants, particularly the greenhouse gas carbon dioxide, CO2. Also, once fossil fuels have been used, they cannot be used again.

Fossil fuels such as crude oil and natural gas can be extracted from under the oceans.

Fig 7.3.2

Fig 7.3.3

Prehistoric life provided the coal, crude oil and gas that we use today. Once these fuels run out, we will have no more. The original source of such energy is the Sun.

Uranium When uranium atoms are bombarded with neutrons, they often split, releasing more neutrons and enormous amounts of energy. So much energy, in fact, that splitting just one uranium atom releases 26 million times more energy than the burning of one molecule of natural gas! This process is referred to as nuclear fission. After World War II, nuclear reactors were built in the hope that fission would produce enough energy to meet the world’s increasing needs. Problems soon arose, however, the most pressing being how to dispose of the dangerous waste products. Radioactive waste can cause cell damage in living organisms and lead to cancer. Many methods of storing nuclear waste have been tried in the past but all are only short-term solutions. The waste can remain radioactive for many thousands of years, but some of these methods have failed after only a few decades. Scientists are currently considering ‘injecting’ waste deep underground into stable beds of a rock called shale, effectively trapping it far beneath the Earth’s surface. These measures are temporary, however—none of the nuclear waste produced in the United States over the past 45 years has yet been permanently disposed of! You will learn more about nuclear energy in Science Focus 4.

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Human intervention: energy crisis! Renewable energy sources Because of the rapid increase in use of fossil fuels, and the ecological impact of this, there is a very real need to find and use alternative and renewable sources of energy. Renewable energy comes from sources that can be used over and over again with minimal impact on the environment. Renewable forms of energy include: • energy from the Sun • energy from the vast quantities of heat stored within the Earth • energy from the action of wind • energy from water—the action of waves, currents or tides, the falling of water due to gravity, or differences in salt content • ‘green energy’—energy derived from wood and other plant matter (sometimes called biomass).

>>> Solar cells The solar cell, or photovoltaic cell, was first developed for the NASA space program and has been used to provide power for satellites and space probes. Solar cells convert light energy into electrical energy. In California, USA, a solar power station has 2000 mirrors positioned to reflect sunlight onto a receiving tower. It generates 10 megawatts of power each day. The computerised mirrors follow the Sun’s path during the course of the day.

Fig 7.3.4

Energy from the Sun Green plants use the Sun’s energy to power their own food production. Some animals use sunlight to regulate their body temperatures. In contrast, humans tend to waste it, rarely using it as a primary source of heat and only sometimes as a source of electrical production. This energy is free and non-polluting, a bonus especially for developing countries that lie near the equator.

Solar ponds In a shallow pool, sunlight es through the water and is absorbed by the base and sides of the pool, gradually warming them. Water that is in with the sides and base slowly gets warmer too. Warm water rises and cool water drops, causing convection currents throughout the pond. These continue until the temperature of the pond is uniform throughout. If salt is added to the water, however, the warm water does not rise, but stays warm at the bottom of the pond. Water pipes running along the bottom of the pond can be used as a way to heat fresh water ing through the pipes. The temperature of the water at the bottom of a solar pond can be as high as 107°C—hot enough to turn special turbines to generate electricity. This method is used in Israel to generate a small percentage of that country’s electrical needs by exploiting the extreme saltiness of the Dead Sea.

206

Fig 7.3.5

A solar-powered telephone exchange—ideal for isolated places such as the Australian outback, where communities are scattered over a vast area and the cost of installing power lines would be too high.

They are extremely useful in remote areas because they have no moving parts to service and require no fuel except sunlight. Solar cells are being used more and more in items as diverse as electronic toys, calculators and solar hot water heaters. Unfortunately the process used for the production of solar cells is not energy efficient and also produces pollution. Solar s are also not very energy efficient and much research is going into improving their performance. Recent research has led to the development of a ‘solar concentrator’—the Winston tube. This instrument concentrates light to intensities similar to that of the Sun’s surface, generating enormous quantities of cheap, non-polluting energy. It has been suggested that by 2010 the Winston tube may be in widespread use in many countries where light is plentiful.

mirror lens can be raised or lowered to control light

reflecting mirrors

the intense light produced by the Winston tube could be used to destroy toxic chemicals

water and carbon dioxide

Named after its American inventor, the Winston tube offers hope for large-scale energy production with little or no pollution.

magma very close to their surface because they lie on fault lines in the Earth’s crust. They are able to use this Hot dry rock geothermal energy to produce One cubic kilometre of electricity: water is pumped hot granite at 2500°C has the stored energy of into the ground, where it is 40 million barrels of oil. heated by the molten rock Australia has large until it boils and produces areas of granite of this temperature at 3 to steam. The steam is tapped 5 kilometres below and turns turbines that the surface. produce electricity. Although this system appears to be ideal, there are some disadvantages: • Only countries near fault lines have easy access to molten rocks beneath the surface. • When water is extracted from or pumped into rocks, underground pressures change, leading to increased likelihood of earthquakes and rock cracking. • Geothermal energy produces a number of gaseous pollutants, particularly carbon dioxide, hydrogen sulfide, sulfur dioxide and methane. Improved technology has greatly reduced the impact of these substances on the environment, however, and the overall effect is less damaging than other sources of energy production.

UNIT

7.3

dangerous chemical waste

Fig 7.3.6

generator building pump house cold water down hot water up

Energy from within the Earth The Earth’s crust is an incredible insulator. Desert animals have long taken advantage of this fact by digging burrows 20–30 centimetres Ring of fire below the surface, where the Most of the planet’s temperature is lower. Without the 850 active volcanoes are the crust, heat from the Earth’s molten in a region called Ring of Fire—around interior would have devastating the edges of the Pacific consequences for life on the Ocean. Within this ring surface. The surface would be as some countries such New Zealand are taking ‘baked’ from below as well as from advantage of geothermal the Sun above. Some countries, power. such as New Zealand, have hot

water heats up hot rocks

Geothermal energy is used in areas where active volcanoes and lava flows are present, or where water heated by deeply buried rocks makes its way to the surface. Water can be pumped down into the ground to be heated by the hot rocks, then pumped back out again.

Fig 7.3.7

207

Human intervention: energy crisis! Tallest geyser The pressure of a geyser Geothermal energy in all its builds up when forms currently produces more underground water is than 7000 megawatts of boiled by underground electricity per year—about 0.15% magma. Currently, the tallest geyser in the of the world’s energy needs. world is the Steamboat At the moment, Australia Geyser in Yellowstone makes only limited use of National Park, blasting water up to 115 metres geothermal energy production. into the sky. The Mulka Cattle Station in South Australia has used it since 1987, and the Garden East Apartments (also in South Australia) have been operational since 1994. Funding has also been provided for a pilot plant in the Hunter Valley, New South Wales. In contrast, New Zealand meets up to 75% of its energy needs through geothermal sources. Other countries using this form of energy production include the United States, the Philippines, Iceland, Russia, Mexico, Italy and Japan.

>>> Energy from the wind Have you ever wondered where the wind comes from? Global winds are the result of hot air rising over the equatorial regions. This process creates a space into which cooler air from the poles rushes. We call this movement of air ‘wind’. Sailing boats and windmills have used wind energy for thousands of years. More recently, windmills have been redesigned using modern materials and technology, greatly increasing their efficiency. Now called wind turbine generators, they convert the energy of wind movement into electricity. This electricity is used directly to do mechanical work, or fed directly into the electricity grid, or it can be stored in batteries for later use. Factors that influence the amount of electrical energy produced include: • the wind speed. The power supplied by the wind turbine generators depends on the wind Is this the future? speed cubed. Thus when the wind speed doubles, the power produced increases eightfold. • the length of the blades. The power supplied is related to the length of the blades squared. This means that when the blade length is doubled, the power is quadrupled. Australia’s first electricity grid connected to a wind farm is located at Crookwell in New South Wales,

Fig 7.3.8

208

Steam rising from a geothermal power plant

From the traditional to the modern: old and new windmills. Wind turbines can now produce enough energy to be considered a viable energy source for the twenty-first century.

Helgoland, an island in the North Sea, combines solar and wind energy, together with heat energy from the sea and a little diesel oil in order to meet its energy needs. A solar-, diesel- or wind-powered heat pump extracts the heat and salt from sea water, giving the islanders not only power to heat their homes, but a supply of fresh water to drink!

Fig 7.3.9

where eight turbines generate 4.8 MW (megawatts) of power. At Blayney, west of Bathurst, New South Wales, 15 turbines generate 10 MW of power. This is enough power for 7000 homes and replaces older technologies that would have produced 16 000 tonnes of carbon dioxide emissions annually. The largest single wind generator is on Kooragang Island, Newcastle, New South Wales. In the future, it is highly probable that wind farming will become a major industry along Australia’s vast coast, with small towns and villages becoming almost totally self-sufficient in their energy production.

Talbingo Reservoir and Tumut 3 hydroelectric power station in the Snowy Mountains

Fig 7.3.10

UNIT

7.3

Energy from water Water provides the backdrop for all life on our planet, and can be used to provide us with energy in a number of ways.

Hydroelectricity Gravity pulls water downhill until it reaches the lowest possible point—the sea. The gravitational potential energy it contains can be harnessed by ing it through turbines to generate electricity. Electricity produced in this manner is referred to as hydroelectricity. There are two ways we can maximise the amount of electricity produced. • Make a small volume of water fall from a great height—the Alps of Europe and the Rocky Mountains, USA, are ideal for this. • Make a large volume of water fall from a much smaller height—dams built on the Amazon River (Brazil), the Nile (Egypt and Sudan) and the Yangtze River (China) all use this method. The largest hydroelectric scheme in Australia is the Snowy Mountains Scheme in New South Wales, which generates almost 3800 MW (megawatts) of power. Consisting of 16 dams and 145 km of tunnels, this series of seven power stations provides 50% of Australia’s hydropower. A further 30% comes from Tasmania. The advantages of this form of energy production are that it uses a renewable source of energy and is pollution free. It can also respond quickly to demand during peaks of energy consumption. There are some disadvantages, however. The construction of dams, and the water they hold, results in large loss of land, and destruction of both natural habitat and towns. As the water is no longer freely moving, the oxygen content falls, and the quality of the dam water reduces to the point where it is often unable to sustain normal fish populations.

Using water currents, tides, waves and salinity Modern technology has given us four ways to produce electrical energy from sea water. 1 Warm water currents in the sea can be harnessed through ocean thermal energy conversion (OTEC) schemes. Warm ocean water is pumped through a pipeline and is used to heat fresh water to boiling point. The steam produced generates electricity. The method is particularly suitable for tropical lands, but is very expensive. 2 Osmosis is the movement of water from a weak solution (having low salinity, like fresh water) to a stronger solution (with a higher salinity, like sea water) through a semipermeable membrane. This membrane allows some molecules to through it (in this case water), but prevents the movement of other particles (salt). Japanese scientists have used osmotic pressure to generate large quantities of pollution-free energy. A disadvantage of this form of energy production is that it is available only to countries that have fresh-water rivers flowing into the sea, Prac 1 where there will be large differences in p. 213 salt concentration. 3 A system of wave energy generators is being developed by both Britain and Japan. Waves are forced into a narrow gully, causing the air above them to rise and fall. This moving air es through a turbine to produce electricity. Because this method relies on situating a power station on

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Human intervention: energy crisis!

Wells turbine turns in same direction irrespective of airflow direction incoming wave forces air out of OWC

Fig 7.3.11

An oscillating wave column (OWC) generates energy by using ocean waves. The waves push air past a turbine, causing it to spin.

rocky cliffs, it has had limited use. Britain is also developing a form of wave generator that floats on the ocean surface. 4 The daily movement of the tides is the only known renewable resource that is totally predictable. The basic engineering behind tidal power generation is relatively simple and is usually achieved by placing a barrier across a bay’s entrance so that the incoming tide turns a turbine. At the maximum height of the tide, the water flow is blocked until the tide is low. The stored water is then released again, turning a turbine to produce electricity. The amount of energy generated is related to the size of the tides. Only a few countries have large enough tides to currently use this technology. The northern coast of Western Australia near Broome would be ideal for this technology, although currently there is little need for it due to the small local population.

Biomass Biomass is the term used to describe organic material that has recently died and which can be used to generate energy. It includes everything from wood from fallen trees or industrial processes to the faeces from humans and animals. The energy that is stored in biomass is referred to as bioenergy, and is usually lost to the environment in the form of heat.

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Comfy compost Looking for a nice warm place to hide out in the winter? Try curling up in the middle of a haystack! If you can’t find a haystack, climb into the compost bin! Both of these examples of biomass release large amounts of heat energy as their material decomposes into its elementary molecules.

retreating wave sucks air back into OWC

The conversion of biomass into bioenergy is, in effect, the process of photosynthesis in reverse. Although the carbon contained in the biomass is converted into carbon dioxide and is released back into the atmosphere, the total amount of carbon dioxide present in the ecosystem does not change. How is this possible? Because the carbon dioxide that is released is equivalent to the amount absorbed by the plant as it was growing.

Energy from timber and agricultural wastes Biomass can be used directly by burning it. Wood can be burnt for heating and cooking but, although it is a renewable resource, it takes Macadamia nut power time for timber to grow. We are A power plant in also using timber faster than it Queensland is producing can grow. For this reason, many 9.5 gigawatts of countries are now choosing to renewable energy per year by using waste plant fast-growing trees that are macadamia nut shells. suitable for coppicing. Coppicing This displaces some harvests only the tree canopy 9500 tonnes of greenhouse gases. and does not kill the tree. Every few years the shoots that have sprouted from the stump can be harvested again. During this time, the roots of thetrees also assist in keeping the soil together to reduce erosion. Indirect use of biomass involves converting it into a suitable fuel that is then used as an energy source. This most commonly occurs with agricultural crops such as sugar cane, corn, rice and wheat, and oil-bearing crops such as sunflowers. Waste products from their harvesting are processed into fuels such as ethanol and biodiesel. Prac 2 p. 214

Energy from industrial and household waste With the increased production of pre-packed and pre-cooked foods, the commercial food industry produces vast quantities of both solid and liquid wastes. These wastes include peelings, pulp, filter sludges and fibrous wastes, together with the water from the washing and blanching of food products. These wastes contain dissolved organic matter, including sugars and starches, and have the potential to produce ethanol when combined with certain anaerobic bacteria. Of the total household waste collected each day, more than 80% is biomass, and of this 46% is organic matter (food scraps and garden waste), 24% is paper, and the remainder is an assortment of plastic materials. This type of waste can be converted into energy directly, by burning, or it can be ‘digested’ by anaerobic bacteria in Source landfill gas plants to produce biogas (methane and carbon dioxide), which can Coal then be used to generate heat and power.

Conservation: the most important ‘fuel’ of all There is one fuel we have not considered yet, and it is possibly the most important of all. It is the ‘fuel’ of conservation: for every joule of energy we do not use, there is one less joule of energy that needs to be produced. If each of us makes an effort to use less energy, then the energy requirements of our cities will be reduced, resulting in less pollution and our resources lasting longer. The Australian Government has a number of subsidies and grants for the development of energy conservation technologies. For example, biofuel producers will receive $37 million in subsidies to help reach the government’s goal of 350 megalitres of renewable fuel production by 2010.

In many developing countries, the manure from cows, camels and other animals is shaped into ‘pancakes’ or ‘bricks’, dried and stored. It is then burned to provide heat mainly for cooking. Animal and human wastes can also be converted to biogas using anaerobic bacteria. The table opposite shows the advantages and disadvantages of r! we po the energy sources Pig f Pigs can only use hal available in the food they eat—the Australia. half is lost as other waste. This waste has k been used at Berryban ere Pig Farm at Winderm near Ballarat, Victoria. Electricity is generated on the site from the breakdown of pig effluent into biogas.

Advantages

Disadvantages

Large Australian reserves Easily mined Low cost Provides export income

Non-renewable Causes greater pollution than oil and natural gas

Oil

Limited Australian reserves Easily transported Many uses

Non-renewable Limited world supplies Causes pollution

Natural gas

Limited Australian reserves Efficient source of domestic heat

Non-renewable Causes pollution, although less than coal and oil

Nuclear

Large Australian reserves High energy output per unit mass of fuel Low accident rate Provides export income

Non-renewable Radioactive waste disposal Security risks

Solar

Renewable Low running costs Efficient heating Causes little pollution

Dependent on weather Large collectors needed

Hydro

Renewable Causes little pollution Low running costs

Dependent on weather Dam destroys local habitat

Wind


Dependent on weather Low energy output

Tidal/wave


Dependent on tides/waves Restricted sites

Biomass

Renewable Biogas uses wastes

Limited rate of supply Low energy output per unit mass of fuel

Worksheet 7.3 Energy in the community

Energy from animal and human waste

UNIT

7.3

(wood, biogas, etc.)

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Human intervention: energy crisis!

UNIT

7.3

[ Questions ]

Checkpoint

Think

Energy sources

17 Describe how fossil fuels are produced.

1 a Identify how energy resources are classified into two major types. b List examples of each type.

5 List three ways we use energy from the Sun.

18 Copy the following, modifying any incorrect statements so they are true. a Splitting atoms to generate energy is called nuclear fusion. b Geothermal power is a source of energy that can be used worldwide. c Hydroelectricity is the electricity produced by harvesting falling water. d Global winds arise from cold air blowing in from the polar ice caps.

6 State the two major benefits of using the Sun as an energy source.

19 Assess why the base and sides of solar ponds are painted a dark colour.

2 Define the term ‘fossil fuel’. 3 Define the term ‘nuclear fission’ and explain why some think it is a desirable energy source. 4 Discuss two disadvantages of nuclear energy.

Energy from the Sun

Energy from within the Earth 7 Define the term ‘geothermal energy’. 8 Describe how geothermal energy is used to produce electricity. 9 Discuss two disadvantages of geothermal energy.

Energy from the wind 10 State the benefits of using wind-powered electricity generators.

20 Your friend cannot understand why coal and gas are called ‘fossil fuels’. Explain to him why these are being used correctly. 21 The oil fields of the Middle East lie under hot and dry deserts. In prehistoric times would you expect these areas to be the deserts they are now, or warm and wet swamps and shallow lakes? Justify your reasoning.

Analyse

11 a Propose a likely meaning for the term ‘wind farming’. b Discuss the advantages and disadvantages of this form of energy production.

22 Consider this statement: ‘The most valuable energy source is conservation’. Do you agree or disagree? Justify your reasoning.

Energy from water

23 List as many ways as you can in which you can help conserve resources.

12 a List the various ways in which water can be used to generate electricity. b Select two of these ways and describe how the energy in the water is used to generate electricity. 13 Define the term ‘osmosis’.

Biomass 14 Define the term ‘biomass’. 15 Explain two ways in which biomass can be used to supply energy.

24 Explain in your own words why the conversion of biomass into bioenergy can be considered ‘the process of photosynthesis in reverse’. 25 a Copy and complete the table below to summarise any five energy sources in this unit. b Consider the energy sources you have summarised and evaluate their potential as future energy sources.

Conservation: the most important ‘fuel’ of all 16 Explain how conservation of energy benefits society.

Name of energy source

212

Description of how energy is produced

Advantages

Disadvantages

UNIT

7.3 [ Extension ] Investigate 1 Design an energy poster. You could include a number of different methods of energy production, or you might look at one specific method in more detail. Include: a whether this is a renewable or non-renewable resource b the advantages and disadvantages of this type of energy source c the requirements for this type of energy source d which countries can use this method of energy production e whether or not it has already been employed as an energy source, and if so, how successful it has been. 2 Research more about the work being done by Australian company Energy Developments in using energy from landfill sites.

Action 3 a Construct a list of the energy wastage in your home. Are lights left on in empty rooms? Do you leave the water running while you clean your teeth? Do taps drip? Do you recycle paper, PET plastics and glass? Does your home have a compost bin? Is your home adequately insulated? How can you improve the energy usage in your home?

UNIT

7.3

Surf Complete the following activities by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7 and and clicking on the destinations button. 5 Explore some Australian environmental issues and State-specific environmental problems. 6 a Examine how to save water, and study environmentally friendly designs for a home. b Design an environmentally friendly house using the information provided. Create an architectural plan of the house, including the environmentally friendly features.

[ Practical activities ] Checking out osmosis

Prac 1 Unit 7.3

b Design a plan of attack on energy wastage, including at least ten points that can be improved upon. 4 Visit your local council and examine what is being done in your community to conserve resources. Does it have ‘green waste’, glass, PET plastic and paper collection? What happens to them after they are picked up?

Aim To observe the movement of water across a semipermeable membrane Equipment Three 10 cm lengths of dialysis tubing, 3 large beakers, distilled water, salt water (two different concentrations), stopwatch

Method 1 Tie a knot in the bottom of each length of dialysis tubing. 2 Label the tubes A, B and C. 3 Fill tube A to three-quarters full with distilled water, and tie off the top with a rubber band. Leave about 3 cm of space at the top of the tubing.

4 Fill tube B to three-quarters full with the lowest concentration of salt water, and tie off the top as before. 5 Place each tube into a beaker of distilled water— the tube should be almost completely immersed. 6 You will find that the volume of liquid in tube B will increase as the water moves into the tube to try and balance the salinity. Using a stopwatch, time how long this process takes. 7 As you did with tubes A and B, fill tube C to three-quarters full with the highest concentration of salt water. 8 Place tube C into a beaker of distilled water and time how long it takes for the tube to become full. 9 Record your results in a table similar to the one overleaf.

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Human intervention: energy crisis! Fig 7.3.12

Peanut power Aim To release the chemical potential energy in

Tube A distilled water

Tube C salt water— high concentration

Tube B salt water— low concentration

Prac 2 Unit 7.3

a peanut

Equipment

Peanut and other nuts such as macadamia, cashews, pecan or walnuts; a cork; large needle; tripod; 100 mL beaker; thermometer; water

Method 1 Carefully push the eye end of a large needle into the smaller end of the cork. 2 Very carefully and gently push the needle into a peanut. If you push too hard the peanut will split. 3 Add 30 mL of water to the beaker. 4 Place the thermometer in the water and record the temperature. 5 Carefully set the peanut alight and place it under the beaker.

distilled water

6 Allow the peanut to burn until it goes out. 7 Record the maximum water temperature reached. 8 Repeat the experiment with different types of nuts. Tube A

Tube B

Tube C

Tick to indicate a movement of water Time taken for water to fill tube

Questions 1 Construct a diagram of the experiment, labelling all parts. 2 Describe how the appearance of the dialysis tubing has changed. Have all tubes changed in the same way? 3 Which molecules have moved across the tubing membrane—the water molecules or the salt particles? Justify your answer. 4 On your diagram, illustrate the movement of molecules. 5 Assess what this tells you about the dialysis tubing. 6 Identify the term for the movement of water molecules across this type of membrane. 7 Was there any difference in the time it took for the water to move into tubes B and C? Explain why.

214

Questions 1 If you used other types of nuts, identify the variable that was changed. 2 Predict what would occur if more than one peanut was used to heat the water. You might like to test your prediction by carrying out the experiment. 3 Determine which nut type contained the most chemical energy.

Chapter review [ Summary questions ]

[ Interpreting questions ]

1 Identify an example of each of the following forms of energy: a nuclear energy c chemical energy b heat energy d light energy 2 Organisms tend to live in relatively small, localised areas. Explain why.

15 What do you think is the most important type of energy? Justify your reasoning.

3 State what the arrows in a food chain show.

18 Deduce the meaning of the statement ‘lightning is a necessary danger’.

4 Determine what percentage of energy is ed on to each level of the food chain. 5 Define the Law of Conservation of Energy. 6 Copy the following, modifying any incorrect statements so they are true. a The unit with which we measure energy is the joule. b Energy that is derived from molten rocks beneath the surface of the Earth is called thermal energy. c Endothermic animals use most of their energy to maintain a constant body temperature. d Bacteria and fungi are decomposers that have a major role in returning atoms in the biotic environment back to the abiotic environment of the ecosystem. 7 Define the term ‘semipermeable membrane’. 8 Explain why coal, oil and gas are described as ‘fossil fuels’. 9 a Define the term ‘hydroelectricity’. b Identify a place in Australia where you will find this form of energy production.

16 Energy and matter both flow through the ecosystem. Distinguish between them. 17 Explain how energy is ed on from a plant to a first order consumer.

19 Assess why it is important to replace trees that have been used to provide heat energy. 20 ‘Bacteria may be small, but they have a big impact on our environment.’ Deduce the meaning of this statement. 21 Evaluate whether the form of ‘wood harvesting’ called coppicing would be beneficial to the environment. 22 Evaluate the implications for society of using more sustainable energy sources. 23 Currently there is no nuclear power plant in Australia. (Lucas Heights in southern Sydney produces radioisotopes used in medicine and engineering.) Evaluate whether introducing nuclear energy into Australia would be beneficial for society and the environment. 24 Discuss the advantages and disadvantages of using the method shown in the photo below, for power generation. Fig 7.3.13

[ Thinking questions ] 10 Construct a food chain that you might find in your local area. Label each of the organisms as either producers or consumers, and their ‘order’ in the chain. (Which ones are first order consumers? Second order?) 11 Construct an energy flow chain for your food chain. What is the original energy source? 12 State a word equation to describe the processes of: a photosynthesis b respiration What do you notice about these two processes? 13 List differing viewpoints about the use of fossil fuels and uranium as energy sources. 14 Identify choices that need to be considered when constructing and furnishing a new home or building.

Worksheet 7.4 Energy in ecosystems crossword Worksheet 7.5 Sci-words

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Sense and control Key focus area

5.2, 5.8.4

Outcomes

>>> The nature and practice of science By the end of this chapter you should be able to: identify parts of the eye, ear, skin, nervous and endocrine systems describe how these organs and systems work identify the specialised cells that give us our senses identify some of the problems associated with the eye, ear and skin, and describe ways to avoid or rectify these problems list five different taste sensations give examples of a stimulus and a response list some hormones and describe their functions identify the specific male and female hormones involved in growth and puberty

Pre quiz

describe how technology allows us to enhance our senses.

1 List our five senses. 2 What is the biggest organ of the human body?

3 What is the advantage of having two eyes and two ears?

4 Why do pimples affect kids more when they go through puberty?

5 What is your body doing right now without any thought from you?

6 Why is it dangerous to dive into water of unknown depth?

7 Why do dogs show so much interest in other dogs’ urine?

8

UNIT

8.1 context

Fishy focusing

Our eyes provide what many would regard as the most important of all our senses—sight. Take a look around you now. If your eyes are working normally, they just transmitted automatically focused colour images of several objects located different distances away to your brain with virtually no effort! But how do eyes work?

Fig 8.1.1

Most animals focus by using the ciliary muscles to change the shape of the lens. Fish, however, focus images by moving each lens backwards and forwards, just like a camera.

Parts of the eye

The eye contains several parts that may remind you of the parts of a camera. When you think about it, both the eye and the camera perform similar tasks—focusing on and capturing images. You may recall from earlier studies of light that images produced by convex lenses are upside down.

The eye focuses images in the retina. Although the image is upside down, the brain processes it so that we perceive it the correct way up.

Prac 1 p. 224

iris retina

lens optic nerve

diaphragm

film shutter

convex lens

Fig 8.1.2

The similarities in the operation of a camera and the eye are obvious.

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Sight

The choroid is a black layer that forms part of the inside lining behind the lens, and prevents light from reflecting all around the eye.

The rest of the eye is filled with a jelly called vitreous humour which helps maintain the shape of the eye.

The retina is a layer containing over 100 million light-sensitive cells which transmit messages to the brain.

The sclerotic layer is a tough, white-coloured protective layer that surrounds the eye and helps maintain its shape.

The yellow spot, or fovea, is a section of the retina directly behind the pupil that contains a large number of colour-sensitive cells. This is why you should look directly at an object to see it most clearly.

The conjunctiva is a clear, thin layer covering the front of the eye. You may have heard of an infection of the eye called conjunctivitis that can occur here.

The blind spot is where blood vessels and the optic nerve the eyeball, and there are no light-sensitive cells to detect image information.

Under the conjunctiva is the cornea, a clear 'window' in the sclerotic layer that allows light to enter the eye. The hole in the centre of the iris is called the pupil. When conditions are dark, the pupil increases in size to let more light in, and is said to be dilated.

The optic nerve s the eye to the brain, allowing image information to be processed so we see images the right way up.

The space between the cornea and the lens is filled with a watery liquid called aqueous humour which helps maintain the shape of the eye.

Just in front of the lens is the iris, which changes size to control how much light enters the eye. It also gives your eye its colour.

The clear lens helps focus an image on the The lens is held back surface of the eye. in place by suspensory ligaments. Depending on how far away an object is, ciliary muscles change the shape of the lens to bring images into focus.

Worksheet 8.1 The eye

The human eye

Fig 8.1.3

Eye protection pupil

bright light

Fig 8.1.4

dilated (dim light)

The pupil adjusts according to the amount of available light.

Prac 2 p. 225

218

There are a number of features that help protect our eyes. Our eyebrows and eyelashes help keep dust out, and tear ducts produce tears to flush out any foreign particles. Our eyes are set back in depressions in our skulls called orbits to give them some protection from being knocked. Warning! Always use protective eyewear in science classes when handling or heating chemicals that could spit or spill from their containers. If a foreign substance does get into your eye, flush it immediately with water while trying to keep your eye open to allow water to the affected area. An eyewash bottle should be available for this purpose.

If red light falls on the retina, ‘red’ cones are activated. With purple light, both red and blue cones are activated. Both rods and cones send messages to the brain to help us see. Some people lack one or more types of cone cells and cannot easily tell the difference between some colours, most notably red and green. This condition is known as colour blindness and affects about 1 in 15 males and 1 in 1000 females.

An eyewash bottle can be used to rinse foreign matter from the eye—make sure you know where one is in your science rooms.

UNIT

8.1

Fig 8.1.5

Why two eyes? Two eyes allow us to judge distances more accurately. Each eye sees a slightly different view. The brain combines the two images to create a threedimensional view that gives us more information about how far away an object is. This is called binocular vision.

Colour vision

Fig 8.1.7

The retina contains special cells called rods and cones. Rods are more sensitive than cones, but respond only to light and dark, helping us to detect shapes. Cones need more light to be activated and come in three types, which detect the colours red, blue and green. A scanning electron microscope photograph of rods and cones

Fig 8.1.6

A colour blindness test. What do you see?

Animal eyes The eyes of various animals are specialised to increase The largest their chances of survival by eyes in the detecting predators or food world more easily. A rabbit’s eyes The giant squid can grow up to 14 metres are positioned on the sides of long and has eyes as its head so that it can see large as soccer balls! most of its surroundings without moving its head and attracting attention. The eagle has excellent eyesight and can detect a rabbit from three kilometres away! Like most predators, owls have both eyes at the front to allow better judgement of distance when swooping on prey. Insects may have multiple lenses to provide an all-round view. Spiders have four, six or eight eyes, and scorpions have Prac 3 between six and twelve. p. 225

219

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Sight A rabbit can see both sides at once.

Fig 8.1.8

Wobbly chook heads Have you ever wondered why chickens wobble their heads so frequently? A chicken’s eyes are on opposite sides of its head, but to judge distance it needs to see an object with both eyes. The only way it can do this is to quickly move its head to view the object with one eye, then the other.

Fig 8.1.10

A chicken must continually move its head to obtain a complete view of its surroundings.

Cats’ eyes Cats’ eyes are unusual for a couple of reasons. They have a slit-shaped pupil which opens and closes much faster than a round one, allowing their eyes to adjust to changes in light intensity more quickly. Have you ever noticed how cats’ eyes shine at night? This is because a mirrored lining at the very back of the eye (called a tapetum) reflects light through the rods and cones a second time, giving the cat more chance of seeing objects even in very dim conditions.

Fig 8.1.9

The forward-facing eyes of the owl give it good binocular vision, allowing it to judge distance as it swoops on prey.

Do animals see in colour? Yes, many animals see in colour, but not the same as we do—it depends on the number and type of cones they have. Some animals, like bees, see colours that we can’t, as they have extra types of cones in their eyes. Birds that are active in daytime are able to see colours, but those that are active at night cannot. Cats, dogs and rabbits are thought to have very poor colour vision, and probably see virtually in black and white.

220

An insect’s compound eye contains thousands of lenses.

Fig 8.1.11

Sheep and horses have good colour vision. Insects can see colours, but not red. Some insects can see ultraviolet light, which is normally invisible to humans.

Eye defects The job of the lens is to bend light so that an image is formed on the retina. It does this by using the ciliary muscles to change its shape. When these muscles relax, they pull on the suspensory ligaments and

Eye focused on a distant object

circular fibres relaxed

image on retina

Eye focused on a near object

circular fibres contracted

image on retina

meridional fibres relaxed

meridional fibres relaxed

light from close object

light from distant suspensory object ligaments taut

suspensory ligaments slack light bent more by fatter lens

light bent little by thin lens

Fig 8.1.12

UNIT

8.1

How the eye focuses on close and distant objects

stretch the lens, making it thinner so it bends light less. When the ciliary muscles contract, they pull less and allow the lens to fatten up. Fatter lenses bend light more, which is what’s required when looking at close objects. The ability of our eyes to change lens shape and focus at different distances is called accommodation. In some people, the lens has become less elastic and is unable to become thin enough or fat enough to focus images at exactly the right position in the eye. Short-sighted people can focus on objects a short distance away, but not on distant objects. This condition is known as myopia. Myopia can be corrected by wearing concave lenses that move the focus point of the image back onto the retina, as shown in Figure 8.1.13. Correcting short-sightedness

Long-sighted people can see long distances away, but cannot focus on close-up objects. Another name for long-sightedness is hyperopia. Hyperopia can be corrected by wearing convex lenses which bend light more so the focus point of the image is brought forward onto the retina, as shown in Figure 8.1.14. Presbyopia is a condition in which a person loses the ability to focus at short distances (e.g. when reading) due to ageing. People with presbyopia often use reading glasses. Bifocal s Some people have trouble focusing The first bifocal lenses were invented by at both short and long distances, and Queensland optical may use bifocal lenses, which have research scientist Stephen two types of lens in one (e.g. convex Newman in 1992. at the bottom for reading, and concave at the top for distance vision).

Fig 8.1.13

close object distant object

convex lens concave lens

close object

distant object

Fig 8.1.14

Correcting long-sightedness

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Sight Fig 8.1.15

lenses can be used to correct impaired eyesight.

As well as spectacles, lenses can be used to correct vision. Soft plastic lenses are available which are more comfortable than hard glass lenses, but are not suitable for everyone. Wearers of lenses must ensure that their eyes still receive enough oxygen. Modern plastic lenses are gas permeable, allowing some oxygen to through to the cornea. The eye may react to a lack of oxygen by growing additional blood vessels to supply Artificial eyes more oxygen via the Medical researchers are bloodstream, but the working on an artificial extra vessels eye that they hope may can cause restore sight to blind people. The artificial eye irritation implants directly into the and other optic nerve. Prac 4 problems. p. 225

UNIT

8 .1

The Lasik procedure being used to correct myopia

Conjunctiva

Fig 8.1.16

Description/function Thin, clear layer covering front of eye

Checkpoint Parts of the eye 1 Compare the eye and the camera, listing similarities and differences. 2 Copy and complete the table above right to summarise each part of the eye described in this section. The first entry has been done for you.

222

Monovision does not mean having one eye! The term refers to vision correction in which a person who is unable to focus at both short and long distances wears a different strength lens in each eye. With time, the brain learns which lens to use depending on the distance of the object being viewed.

A recent development in eyesight correction is laser surgery. Two main methods are PRK (photoreactive keratotomy) and Lasik (laser in situ keratomileusis). PRK involves removing a layer of cells from the surface of the cornea and remodelling the shape of the cornea using a laser. With Lasik treatment, a thin flap of the cornea is lifted up, but not removed, and a laser is used to reshape the cornea before the flap is replaced over the laser-treated area. Patients undergoing Lasik feel less discomfort and healing time is reduced, while with PRK there is more cornea to work with.

Part

[ Questions ]

Monovision

Laser surgery

3 Describe ways in which the eye is naturally protected.

Colour vision 4 Identify the light receptor in the retina that detects: a light or dark b colour 5 Explain what causes colour blindness.

UNIT

8.1 Animal eyes 6 Describe two facts you find interesting about animals’ eyes. angle of vision

7 Define ‘tapetum’.

Eye defects 8 State the common names for hyperopia and myopia. 9 Define ‘presbyopia’. 10 Illustrate what happens to the light path in the eye of a short-sighted person. 11 Describe how defective vision can be corrected. Illustrate your answer.

Think 12 Identify where most of the bending of light occurs in the eye. 13 Propose a reason why the choroid is black and explain what might happen without it. 14 There are no light-sensitive cells in the blind spot. Explain why. 15 When you walk indoors after being outside in bright sunlight, it is very difficult to see well for a short while. Explain why. 16 Explain why we squint when suddenly exposed to bright light. 17 If we had only one eye, state what we would not be able to do as well. 18 Explain why it is important for insects and animals active during daytime to see colours. 19 How good do you think an owl’s colour vision is? Explain your answer. 20 Explain why some racehorses wear blinkers. 21 Identify the parts of the eye involved in focusing. 22 Distinguish between Lasik and PRK surgery. 23 Clarify the purpose of blinking.

Analyse 24 Robert can drive safely without glasses, but has trouble reading the street directory without them. a Identify the condition Robert may have. b Explain why you have selected this condition. 25 If an insect’s eye provides almost all-round vision, images of the Sun must be frequently produced. Propose why the Sun does not appear to damage insects’ eyes. 26 Explain why we virtually only see black and white and very little colour when outside at night. 27 Can you tell for sure whether you see the same colours as other people? Discuss. 28 Justify the need for humans to have two eyes.

Fig 8.1.17 29 The approximate angle of vision for a person is shown above. Draw diagrams to demonstrate the approximate angle of vision for: a an owl

b a rabbit

[ Extension ] Investigate 1 a Use Word or PowerPoint to construct an eye chart. b Use your chart (on screen or a printed version) to test the sight of several people. 2 a Investigate some other eye defects such as glaucoma or cataracts, and their possible treatments. b Produce a brochure for a doctor’s waiting room that outlines the defect, its signs, symptoms, and treatments available. 3 Create a poster to explain how a camera works. Describe how an image is captured on film and developed. Compare this to how our eyes capture and process images. 4 Investigate the Braille system used by blind people to read.

Surf Complete the following activities by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. 5 Examine an online dissection of a cow’s eye. 6 Explore further information about the eye and perform an interactive labelling of the eye’s structure.

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Sight

UNIT

8 .1 [ Practical activities ] Fig 8.1.19

Eye tests Prac 1 Unit 8.1

Aim To construct a mini eye chart and to find your eye’s blind spot Equipment Pen and paper or card

Method PART A: Your yellow spot 1 Use a centimetre grid to draw a larger version of the mini eye chart shown in Figure 8.1.18.

R N F

3 Gradually bring the textbook closer and note when the dot disappears. This happens when light from the dot falls on your right eye’s blind spot. 4 Repeat with your left eye open and right eye closed. PART C: Distance perception 1 Have a partner hold a pen upright at arm’s length as shown. 2 With one eye shut, try to vertically line up another pen to touch your partner’s pen. This may take several attempts.

S K R N F S K • K S F N R K S F N R Fig 8.1.18

Mini eye chart

2 Hold the chart about 20 cm from your right eye while shutting your left eye. 3 Stare at the dot in the middle of the chart.

3 Repeat steps 1 and 2 with the other eye shut.

4 Note which letters you can make out clearly (do not memorise them).

4 Try again with both eyes open.

5 Repeat, this time looking with your left eye while shutting your right. PART B: Your blind spot

224

Fig 8.1.20

Questions 1 a State the number of letters you could see in part A. b Calculate a class average.

1 Hold the textbook at arm’s length and look directly at Figure 8.1.19.

2 a At what distance from your eye did the cross disappear (when its light fell on your blind spot)? b Compare this with others in your class.

2 Shut your left eye, and stare at the cross with your right eye.

3 Evaluate your ability to judge distance with one eye only, compared to two eyes.

Prac 2 Unit 8.1

Persistence of vision

Angle of vision

Aim To investigate the persistence of images

Design an experiment to test the ability of humans to see objects at various angles when keeping the head still. Over what angle can people see? How well can they distinguish objects and colours at extreme angles?

formed by the eye

Prac 3 Unit 8.1

Equipment

Wooden rod (e.g. bamboo skewer), stiff white cardboard, pencils, sticky tape, scissors

Method

UNIT

8.1

DYO

1 Construct the apparatus shown in Figure 8.1.21. Fig 8.1.21 rod

Eye dissection Aim To identify the main structures of the eye

card Prac 4 Unit 8.1

tape

Equipment A pig’s eye or cow’s eye, sharp fine scissors, paper towel, dissection board, newspaper

Method 1 Place the eye on a dissection board on some newspaper and carefully trim any fat or muscle away from the outside of the eye. 2 Sketch the eye, labelling any parts you can identify.

drawing of cage

drawing of bird

3 Carefully cut a hole in the back of the eye near the optic nerve. 4 Hold the eye so it ‘looks’ at a window, and look through the hole you cut at the back of the eye. What do you see?

3 Study the effect of various speeds of rotation.

5 Use scissors to remove the lens from the front of the eye. Describe the shape of the lens. Place it above a scrap of newspaper containing small text. Press down on the lens. How does this affect the view of the newspaper?

Questions

Questions

1 Explain what is meant by persistence of vision as it applies to this activity.

1 Describe the appearance and consistency of each part of the eye.

2 Describe the difference caused by varying the speed of rotation.

2 Determine which way up the image appeared when you looked through the rear of the eye.

3 Compare this activity to movies at the cinema (which some people refer to as ‘the flicks’).

3 Explain why the lens is flexible.

2 Look at the card and spin it about the central rod.

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UNIT

context

8.2 detecting sound waves. They also sense the position of our head, helping us to keep balance. The ears are thus really two sense organs in one.

When we cross a road, our ears can warn us of approaching traffic before we see it. In sport, sound helps players decide who to a ball to when their eyes are directed elsewhere on the field. Our ears work by

Sound Sound travels though air at about 340 metres per second, in waves of vibrating air particles. When the sound wave reaches our ears the vibrations travel through the auditory canal and in turn cause the eardrum to vibrate. The various parts of the ear then convert the sound energy into electrical impulses, which are sent via nerves to the brain for interpretation. The loudness of sound is measured in decibels (dB).

Parts of the ear The ear consists of three main sections: the outer, middle and inner ear. The outer and middle ear are filled with air, and the inner ear is filled with fluid. Fig 8.2.1

The outer ear consists of the highly visible pinna, which helps to collect sounds and funnel them into the auditory canal. The auditory canal connects the outer ear with the eardrum or tympanic membrane. The eardrum is the beginning of the middle ear and is made of a thin sheet of muscle and skin that vibrates in response to sounds. Vibrations are ed to a set of three tiny bones: the hammer, anvil and stirrup. This group of three bones is known as the ossicles. By the time the sound reaches the stirrup, it has been amplified to about 30 times louder than at the eardrum. The stirrup vibrates against a section called the oval window at the boundary between the middle ear and inner ear, causing vibrations to into a coiled, fluid-filled tube called the cochlea. This fluid es vibrations to a layer of tiny hairs connected to auditory nerves. These send messages to the brain, which are then interpreted as sounds.

The human ear

stirrup anvil hammer

oval window

semi-circular canals to brain

pinna auditory nerve

cochlea

ear canal ear drum outer ear

226

eustachian tube round window

middle ear

inner ear

Bang the drum The eardrum is delicate and can easily be broken. Sharp, loud noises such as explosions can rip it, as can things inserted in the auditory canal. Never put anything smaller than your little finger into the auditory canal. Even cotton buds are too small. They can easily reach the eardrum and rip it.

Above the cochlea are the semicircular canals. There are three sections, each perpendicular to the others (like two walls and a floor that meet at the corner of a room). These contain fluid which moves when we do. Nerves send messages to the brain, which in turn signals muscles to help us keep our balance. Worksheet 8.2 The ear

Why two ears? Two ears help us determine the direction of a sound. If a sound reaches both ears at the same time, our brain interprets this to tell us that the source of the sound is directly in front of, behind or above us. If a sound reaches, say, the left ear before the right ear, the brain tells us that the source of the sound is to our left. Fig 8.2.2

Popping ears Sometimes when you climb to a higher altitude, you experience an uncomfortable ‘blocked ear’ sensation. This is caused by a pressure difference between the outer and middle ear. When climbing (e.g. in an aircraft), the outer ear responds quickly to the falling pressure, but the middle ear lags behind and is at a higher pressure. The resulting pressure difference causes the blocked feeling. Eventually the Eustachian tube opens and allows air to rush out of the middle ear so pressure on both sides of the eardrum is again equal. Some people experience a ‘popping’ sensation when this happens. When descending, air rushes into the middle ear to increase pressure to the same as that in the outer ear. If the Eustachian tube gets blocked due to an infection such as a cold, pressure differences will once again give that ‘blocked ear’ sensation.

Prac 1 p. 230

Two ears help us locate the direction of a sound.

the flattened hairs take some time but do recover. This gives partial deafness and ringing in the ears. As these hairs recover so does the hearing, but not completely. Some hairs are flattened permanently and destroyed. Repeated rock concerts will destroy more hairs, leading to more permanent deafness. A blow to the head or a very loud sound (e.g. an explosion) will rip the eardrum. A small tear in the eardrum may heal itself but usually leaves permanent scarring. This interferes with its vibration, so the hearing impairment is also permanent. Damage to the nerves cannot be repaired at all and results in permanent hearing loss. Deafness and partial deafness can be due to a number of things. Wax is produced in the auditory canal to help prevent entry of dust and bacteria. A build-up of wax can stop the eardrum from vibrating correctly, causing temporary deafness. A doctor can easily cure this by flushing out the excess wax with warm water. The ossicles may get jammed together due to exposure to loud sounds or infection, so that vibrations are not ed on to the cochlea. Some people are born with ear defects that reduce the amount of vibration reaching the auditory nerves. Hearing aids work by amplifying sounds and transmitting them to the auditory canal. If the cochlea is damaged, however, hearing aids may not be as effective, since unclear signals to the brain are produced, even if they are amplified. An Australian invention known as the cochlear implant or bionic ear can restore a degree of

UNIT

8.2

Coo-eee

right ear detects sound first

Ear problems Ears in your armpit! A grasshopper’s ears are not on its head, but on each side of its body, below its wings.

Prolonged exposure to loud sounds can flatten the hairs of the cochlea. Hence when leaving a loud rock concert, the hairs have been flattened by the intensity of the noise. Most of

A hearing aid amplifies sound.

Fig 8.2.3

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Hearing

Beethoven’s genius

transmitter coil

most One of the world’s greatest and l sica clas of famous composers wig Lud rn -bo man Ger was music van Beethoven (1770–1827). age Beethoven became deaf at the ed of 30 but, amazingly, continu and ing tand outs e pos to com beautiful music.

mastoid bone

microphone receiver-stimulator cochlea behind-the-ear speech processor

auditory nerve

body worn speech processor

Fig 8.2.4

A bionic ear has several components.

hearing to some people. The bionic ear replaces a nonfunctioning inner ear. It consists of a microphone that sends information to a small speech processor worn behind the ear or attached to a belt. The speech processor sorts out which information is important for understanding speech, transmitting it to a receiver–stimulator implanted in the mastoid bone. The receiver–stimulator then produces electrical signals in probes embedded near the cochlea. These are detected by the nerves and transmitted to the brain.

If you are to operate noisy machinery, mow the lawn or use power tools, your ears may be in for prolonged exposure to loud sounds. The use of small earplugs or earmuffs will electrode array protect your ears and avoid ringing in your ears, which can last for several hours. Any ringing in your ears after exposure to loud sound means that some permanent damage has been done to your hearing. Tinnitus, a condition in which a person hears a permanent ringing in the ears even when there is no sound, can be caused by Prac 2 exposure to loud sounds over a long period p. 230 of time. Use this chart to work out which sounds will harm your hearing.

Fig 8.2.6

Decibels (dB) 160

Worksheet 8.3 Hear hear!

150 140

Dangerous

Harmful

Ear protection

jumbo jet on take off

130 120

threshold of pain

110

loud thunderclap

100 90 80

train motor mower

Loud

70 60

normal conversation

Quiet

Normal

50 40 30 20 10 0

Ears should be protected when exposed to loud sounds.

228

Fig 8.2.5

whisper

quietest sound that can be heard

blah blah blah

UNIT

8 .2

UNIT

8.2 [ Questions ]

Checkpoint

Ear protection

Sound 1 State the word that best describes the movement of air, fluid and bones within the ear when a sound es through it. 2 Identify the unit used to measure the loudness of sound.

Parts of the ear 3 Copy and complete the table below to summarise each part of the ear described in this section.

14 Identify three common situations in which some form of ear protection is advisable. 15 Use Figure 8.2.6 to identify some sounds that can be: a dangerous b harmful c quiet 16 State the sound level in decibels at which sound becomes hazardous to your hearing.

Think Part Pinna

Description/function Fleshy ear flap, collects sound

17 Identify an example of a task that involves mainly hearing. 18 Propose a reason why airlines sometimes offer lollies to travellers during takeoff and landing. 19 Propose a reason why animals like rabbits, deer and zebras have large ears.

4 Identify the part of the ear that is filled with fluid. 5 Identify the three small bones in the middle ear and state the name for them as a group. 6 Identify the part of the ear that the auditory nerves attach to. 7 State where most sound amplification happens in the ear.

Why two ears? 8 A sound arrives at your right ear just before it reaches the left. State which direction the sound came from. 9 Sounds from directly in front arrive at both ears at the same time and so do sounds from directly behind. Propose how we know which direction it is coming from.

Ear problems 10 Propose a reason why there are three semicircular canals instead of just one. 11 Describe how ear wax may be: a useful b a hindrance 12 Describe two ways in which damage can be done to your hearing.

20 Evaluate whether two ears are more valuable than one for survival. 21 Explain why an ear infection may upset your sense of balance. 22 In young children, the Eustachian tube is almost horizontal. In the adult ear shown in Figure 8.2.1, this tube is nearly vertical. Use these facts to explain why young children are more prone to middle-ear infections. 23 Caleb and Sarah both have hearing difficulties. Speaking louder to Caleb makes it easier for him to hear, but it makes no difference to Sarah’s hearing. Propose a reason for this. 24 For each of the following sounds state the approximate decibel level, and whether the sound will damage the ear. Use figure 8.2.6 to help you decide. a Motor mower b Large truck ing by c Helicopter up close d Person shouting at 1 metre away e Formula one racing car from the side of the track f Normal level of music through headphones g Normal classroom chatter.

13 Explain what happens to your hearing after a loud rock concert.

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Hearing

[ Extension ] Investigate

Action

1 Investigate how a stethoscope works.

4 a Design an experiment in which a sound level meter measures the sound levels produced by different walkmans. Record DYO your results in an appropriate table and column graph. b Evaluate your results to determine whether the levels at which you regularly listen are harmful to your hearing.

2 Investigate more about how the bionic ear works. Illustrate the important parts of the bionic ear to show how it functions. Who was the first recipient of a bionic ear?

Create 3 Construct a model ear to demonstrate how the ear works, labelling the important parts. Demonstrate the path of sound energy through the ear and the energy transformations that occur.

UNIT

8.2 Prac 1 Unit 8.2

DYO

Surf 5 Explore information about the ear by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button.

[ Practical activities ] Hearing tests

Reading decibels

Aim To examine the directional ability of our ears in detecting sounds

Aim To measure the sound level of various sounds around the school

Method Seat one of your group and blindfold them. Ensure they are facing straight ahead. Develop a test that will indicate how well they can detect a sound coming from various directions. Test what effect changing distance and blocking one ear have on your results.

Questions 1 Describe how the distance of the sound source affects results. 2 Describe what happens if the person covers one ear. 3 Evaluate the need for two ears.

Prac 2 Unit 8.2

Equipment Sound level meter

Method Each sound level meter operates slightly differently. Acquaint yourself with how to measure and read the sound level. 1 Use the meter to measure at least five different sounds around the school. For example, you might measure the sound levels of two people chatting and then arguing, a noisy classroom, and traffic on the road outside the school. 2 For each measurement, estimate your distance from the subject.

Questions 1 Use a table to record your sound level measurements. 2 Use the table and Figure 8.2.6 to classify each of the sounds as harmful, dangerous, loud, normal or quiet.

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UNIT

context

8. 3 It is said that we have five senses. Sight and hearing are provided by the eye and the ear. Three other important sense organs are the nose, tongue and skin, responsible for the senses of smell, taste and touch respectively. Imagine life without these sensations!

Smell You detect a smell because a few tiny chemical particles enter your nose and dissolve in its moist lining. Considering some of the nasty smells we detect each day this may not be a pleasant thought! The dissolved substance triggers nearby nerve cells in the upper part of the nasal cavity, called olfactory cells. Impulses in the olfractory nerve send messages to the brain so we can smell the substance. The typical human nose can detect around 2000 smells, and may be trained to Prac 1 detect up to 10 000. p. 235

Ahh—choo!

The male fruit fly can Sneezing is a reflex action that detect smells emitted by removes irritating dust or other a female fruit fly using foreign particles from the nasal chemically sensitive hairs on its front legs ages. A sneeze can travel at and its antennae. 160 kilometres per hour right across a room, so duck next time one comes your way! You also close your eyes when you sneeze—some say to stop your eyes from popping out!

Taste The surface of the tongue is covered with thousands of bumps, called papillae. More than 10 000 taste buds are embedded between the papillae. Humans can detect five primary taste sensations: sweet, sour, salty, bitter and umami. Umami is distinctly different from the other basic tastes and is believed to activate a separate set of taste receptors. It is the savoury taste Scanning electron microscope image of a taste bud (centre) surrounded by papillae

tiny particles from pizza

Smelling without a nose

Fig 8.3.2

brain moist lining

mmmmm!

nerve cell (olfactory cell) pizza

Fig 8.3.1

How we detect smells

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Smell, taste and touch of glutamate found in processed meats, cheeses and monosodium glutamate (MSG). Saliva in our mouths must first dissolve samples of food so that the taste buds can detect them and send messages to the brain. A single taste bud contains fifty to one hundred taste cells, which can detect all five taste sensations. Our taste buds also provide information on the intensity and pleasantness or unpleasantness of taste. Although all areas of the tongue are able to detect all taste sensations, some areas Prac 2 Prac 3 Prac 4 p. 235 p. 236 p. 236 may be more sensitive to certain tastes.

Flavour When we eat, our senses of smell and taste work together Artificial to detect flavour. flavouring As much as 80% of Many processed foods what we perceive as rs. have artificial flavou Although made in flavour is actually laboratories, they are smell. Flavour is often identical to those largely the smell of the found in nature. If gases emitted from banana flavouring amyl acetate is distilled from food that has just bananas, it is classified been taken out of as a natural flavouring. your mouth. When Amyl acetate is also made in the laboratory your nose is by mixing vinegar with blocked, your sense amyl alcohol, using of smell is not as sulfuric acid as a good as usual. catalyst. Although exactly the same flavouring, That’s why food it is now classified as seems less tasty artificial flavouring. when you have a cold. Likewise, pinching your nose will make food you don’t like more tolerable. The tongue is most sensitive at temperatures between 20°C and 30°C. Sweet and sour tastes are increased at higher temperatures, and bitter and sour increase at lower temperatures.

Touch Most of us probably don’t think of the skin as an organ, but it is.

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It contains millions of nerve endings that send information about touch, pain, pressure and temperature to the brain. In humans, the touch receptors are more concentrated in the face, tongue, lips, fingertips and toes. Body hair also plays an important role in our ability to sense touch. A large number of receptors are found in the skin at the base of hair follicles.

pain receptor

The biggest organ The average human adult has a 290 g heart, 1090 g of lungs, 1330 g of brain and 1560 g of liver. At nearly 11 kg, however (10 886 g to be exact), the skin is by far the largest organ. Over an average lifetime, a human will shed roughly 18 kg of dead skin!

layer of dead skin

hair

sebaceous gland light receptor

pore

epidermis

dermis

sweat gland

fattty layer pressure receptor

cold receptor

hair movement

heat receptor

A cross-section of human skin

Animal tongues The giant anteater’s tongue may reach lengths of over 60 cm. Dogs do not sweat. Instead, they use their tongues to cool down. Rapid panting at rates of up to 200 times per minute allows heat to be removed from the dog’s body as moisture evaporates from the tongue.

Fig 8.3.3

Below the top protective layer of dead skin cells is a ‘living’ layer of skin. It has different nerve receptors located at varying depths. Thermo receptors respond to heat and cold, and there are about four times as many heat receptors as cold receptors. Pain receptors are located throughout the skin and can experience prickling pain (fast pain) or burning and aching pain (slow pain). The sebaceous glands produce oil that helps keep the skin soft and stops it cracking. The sweat glands produce sweat, which, on reaching the surface, removes Prac 5 p. 236 heat from the body when it evaporates.

Skin conditions Many conditions may affect the skin. One of the most common is acne, which causes pimples to appear, often on the face. Pimples often occur more severely during puberty, when the skin secretes more oil than usual from the sebaceous gland into a hair follicle. Dead skin cells or dirt can block the follicle. If it becomes infected with bacteria, it can become swollen with pus. Contrary to popular opinion, diet has little to do with pimples. Apart from puberty, other possible causes include stress, medications and some cosmetics. Pimples may be treated with pharmaceutical creams and lotions, and by gently washing the affected area. Over-washing and harsh soaps should be avoided. Dermatitis is a condition in which the skin becomes itchy and swollen and exhibits a red rash. It may be caused by exposure to certain chemicals. Eczema is a common type of dermatitis. Warts are harmless, rough, raised lumps that grow on the surface of the skin. They are caused by a virus, and can spread to other parts of the body if scratched open. Chemical treatments are available, or warts may be frozen off by a doctor with liquid nitrogen. Freckles are darker spots caused by a pigment called melanin in the skin cells. Darker-skinned people have more melanin in their skin than those who are lighter-skinned. Freckles are normally harmless, but any change in the size or shape of one should be referred to a doctor. Moles are raised, dark spots that are normally harmless, but have the potential to develop into skin cancer. Again, any changes to a mole should be referred to a doctor.

Skin cancers There are three main forms of skin cancer. Basal cell carcinoma (BCC) is the most common form, and the least dangerous, appearing as a red, flaky or waxy bump on the skin. It rarely spreads to other parts of the body, provided it is treated as soon as possible. Squamous cell carcinoma (SCC) is not as common, and is more serious, appearing as red scaly sores, and can spread to other parts of the body. Melanoma is the least common, and most deadly, form of skin cancer. New spots, or old spots that change colour or size, or itch or bleed, may be a sign of a melanoma, and should be checked immediately. The major cause of skin cancer is exposure to ultraviolet or UV radiation. Unfortunately, Australia leads the world in skin cancer rates. Sunbaking is the deliberate exposure to UV radiation to get a ‘suntan’ and is a very dangerous practice. A suntan is a sign that damage has been done to the skin, whose reaction is to produce more melanin and go darker. Sunburn is even worse, since the damage is more severe and more immediate. Nowadays most of us cover up, using hats and protective clothing and swimwear, or stay in the shade and use sunscreens to reduce the damage caused by UV rays. UV levels from the Sun are most dangerous between 11 am and 2 pm during summer. Whatever the time of day, even on cloudy days, UV rays are always present and damaging.

UNIT

8.3

Worksheet 8.4 The skin Worksheet 8.5 Senses and codes Skin cancers a Melanoma b Basal cell carcinoma (BCC) c Squamous cell carcinoma (SCC)

Fig 8.3.4

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Smell, taste and touch

UNIT

8.3

[ Questions ]

Checkpoint

15 Besides taste, describe what else the tongue is used for.

Smell 1 True or false? a When you smell a substance, tiny parts of it have dissolved inside your nose. b Olfactory cells are nerve cells in the nose. 2 Draw a diagram to demonstrate where the olfactory cells and olfactory nerves are in the nose.

Taste 3 Are papillae the same as taste buds? Explain.

16 Evaporation of sweat from the skin helps remove heat from the body. Describe how.

Analyse 17 Smells may be categorised as: burned, foul, fragrant, fruity, resinous (e.g. nail polish) or spicy. State an example of each type of smell. 18 Write a paragraph explaining how to reduce your risk of getting skin cancer.

4 List a food that would give each of the different types of taste. 5 State the senses that combine to help us appreciate flavour. How could you more easily eat a food or vegetable you don’t like?


Touch 6 Starting from the surface, list in order the layers of the skin.

1 Determine what pheromones are and how insecteating plants use them.

7 List five types of skin receptors.

2 Research the history of perfumes. Possible ‘leads’ include: Ma Griffe, Dior, Nina Ricci, Guerlain, Givenchy and Estee Lauder. Summarise your information in a timeline.

8 Explain the purpose of the fatty layer of the skin.

Skin conditions 9 Briefly describe two skin conditions. 10 Propose some reasons why Australia has such a high skin cancer rate compared to other countries. 11 Outline how you can be ‘sunsmart’.

Think 12 Copy and complete the following table. Sense

Sense organ

Sight The ear Smell The tongue

3 Research other skin conditions, and their causes and treatments. Possible conditions to research include tinea, boils, cold sores, thrush, ringworm, scabies, shingles and psoriasis. a In small groups, present your information to the class using a presentation media such as PowerPoint. b Use peer assessment to evaluate the effectiveness of the presentation. 4 a Research skin cancer statistics over the past decade or so. Is it increasing or decreasing? What reasons could you suggest? Comment on your findings. b Analyse whether increased awareness of the dangers (e.g. through the media or doctors) has had an impact on the occurrence of skin cancer. c Examine what it means if a sunscreen is ‘factor 15’ or ‘SPF 15’. Are other factors available? 5 Create a poster promoting ‘sunsmart’ behaviour.

13 A chemical is added to normally odourless liquid petroleum gas (LPG) to make it smell unpleasant. Explain how this makes LPG safer. 14 Identify a profession or situation in which the senses of smell and taste are important.

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Surf 6 Explore information about the nose and skin by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button.

UNIT

8.3 Smell fatigue Prac 1 Unit 8.3

Aim To investigate the phenomenon of smell fatigue Equipment A safe, strong-smelling substance (e.g. aftershave, soap or perfume), a watch, a small container (e.g. a film canister and lid)

3 Re-seal the container and wait 30 seconds before taking a similar whiff. Rate the strength of the smell from 0 (no smell) to 5 (the strength of your first smell). 4 Continue to take a whiff every 30 seconds, giving the strength of the smell a rating each time until you have about six ratings.

Questions

Note: Check with the class for students who may be allergic to any of the substances to be used in the experiment.

1 Describe what happens to the strength of what you smell after several whiffs.

Method

2 Construct a graph to display your ratings.

1 Obtain a sample of a safe, strong-smelling substance in a container that can be sealed. 2 Carefully take a small whiff of the substance. Do not breathe in too deeply. Avoid taking your breath away.

3 Record whether each area is sensitive to the solution (e.g. sweet).

Taste regions Aim To determine whether some areas of the

4 Repeat for the other three solutions.

tongue are more receptive to certain tastes

Questions

Equipment

1 Record your results on a copy of Figure 8.3.5 but without the marked zones.

Clean cotton buds, samples of the following solutions in new plastic cups (do not use beakers or other lab glassware): sugar, salt, vinegar or lemon juice, coffee

2 Compare your results with those of your classmates. Figure 8.3.6 is the tongue map usually proposed in textbooks. 3 Compare your own map to this.

Method 1 Dip a cotton bud in one of the solutions and touch it to each area of your tongue (shown as A, B, C and D below).

4 Using your own and class results evaluate the accuracy of the map below.

Fig 8.3.5

B

A

D

C bitter

sour

sweet

r

Prac 2 Unit 8.3

2 Do not share cotton buds with others in the class. Use a new end for each sample.

sou

UNIT

8 .3 [ Practical activities ]

sweet and salty

E Fig 8.3.6

This taste map has been presented in many textbooks. How accurate do you think it is?

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Smell, taste and touch

Brand name versus no name Prac 3 Unit 8.3

Skin receptors

Aim To compare the taste of various products

Prac 5 Unit 8.3

and investigate the role of smell in the taste process

Equipment

Aim To investigate the sensitivity of your skin in various areas Equipment Toothpicks, tape, ruler, blindfold

Method

Samples (in pairs) of various edible substances, e.g. ‘brand name’ chocolate, ‘no name’ chocolate, brand name lemonade, ‘no name’ lemonade; blindfold; new plastic cups

1 Attach two toothpicks to a ruler as shown.

Note: Check with the class for students who may be allergic to any of the products to be used in the experiment.

toothpick ruler

Method 1 Work with a partner or group and blindfold one person.

0

1

2

3

4

5

6

7

8

2 Give the blindfolded person a taste of a ‘brand name’ and ‘no name’ pair of foods, and record their brief description of the taste of each. 3 Repeat for the other food items. You may wish to share the blindfold and tasting job among your group . 4 Repeat the tests, but have the tester pinch his or her nose shut while tasting.

Questions 1 Were testers able to distinguish between brands of foods? Give details. 2 Did removing the ability to smell affect the results? Explain. 3 Evaluate any relationship between product brand and quality of taste.

9 10 11 12 13 14 15 16 17 18

20 21 22 23 24 25 26

28 29 30

tape

Fig 8.3.7 2 Make sure your partner cannot see while you touch both toothpick points to a region of skin. Ask your partner how many points they feel. 3 Move the toothpicks closer to each other and test again. Progressively move the toothpicks closer together until only one can be felt. 4 Test other regions of the skin the same way. Some possible areas to try are the back of the hand, palm, inside forearm, back of forearm, leg, foot, back of neck. 5 Swap jobs and have your partner test you.

Questions 1 Give each area of your skin a sensitivity rating.

Prac 4 Unit 8.3

DYO

236

Taste trickery

2 Compare results with your partner.

Design and carry out an experiment to test whether a blindfolded person who is pinching their nose can tell the difference between the taste of apple, potato and pear.

3 Propose reasons why some areas are more sensitive than others.

UNIT

context

8. 4 Through our senses we are constantly receiving information from our surroundings. This information may be of many types: the smell of a classmate’s tuna sandwich, the hot air near a Bunsen burner or the noise of a ing bus. When this information is received it could lead to a variety of responses: holding your nose, moving away from the flame or turning towards the bus. Our responses enable us to react to changes around us, enhancing our chances of survival in a world full of potential threats.

Responding to stimuli One of the fundamental characteristics of living things is that they respond to information received from their surroundings. This ability is needed to feed, escape, move, reproduce and keep warm or cool down. Humans respond to increased temperature by involuntarily sweating and increasing blood flow to the skin (making you look ‘flushed’). Our behaviour changes too: we remove clothes and grab a cold drink. Humans show an amazing ability to respond to changes in their surroundings. For instance, the body temperature of humans stays at approximately 37°C, and blood acidity or pH at around 7.38 regardless of whether they are in the deserts of Africa, the jungles of South America or the icy Arctic zones. This maintenance of a constant internal environment despite changes in the surroundings is called homeostasis. Homeostasis allows cells to keep working efficiently, maintaining temperature, glucose and water levels within strict limits.

Stimulus Heat or cold

Thermoreceptors in the skin

Water levels in blood

Osmoreceptors in the brain and large arteries

Pressure and touch

Mechanoreceptors in the skin

Sound

Cochlear cells in the inner ear

Light

Photoreceptors in the retina of the eye

Chemicals

Chemoreceptors on the tongue and in the nose

Gravity

Semicircular canals in the ears

contains receptors to detect all these stimuli. When a receptor receives a stimulus, a message is Prac 1 Prac 2 sent to an effector. An effector is p. 240 p. 240 an organ, such as a gland or a muscle, which causes a response. A simple example of the stimulus–response model is what happens when you burn your finger

finger cut by knife

stimulus

muscle contracts to withdraw hand from knife

pain receptors

response

receptor arm muscle

Stimulus–response model Homoeostasis requires a sequence of steps known as the stimulus–response model. The sequence begins when a sense receptor is stimulated. A stimulus is something that acts on a receptor, causing a change in the activity of an organism. Stimuli include heat, light, pressure, touch, sound, chemicals and water levels. Your body

Location of receptor

relay by nerves effector

Fig 8.4.1

The stimulus–response model of what happens when you cut your finger

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Responding (the stimulus). Heat and pain receptors in your finger send messages via nerves to an arm muscle (the effector), causing the muscle to contract and pull your hand away from the flame (the response).

and coordination Often this sequence of events involves some kind of of information. The response generally affects the original stimulus in some way, so the organism is able to adjust its response. The total response of an organism is often complex, involving several parts of the body. For this to occur, some kind of coordination is required. All organisms are coordinated in some way. Even a single-celled amoeba can respond to changes in temperature or pH. The response usually involves moving away from the stimulus. In most larger organisms there are a Thermostat number of structures to detect, transmit, coordinate and respond to stimuli. The control of carbon dioxide levels in your blood is an example of the stimulus–response model that includes both and coordination. Blood carbon dioxide levels may rise (the stimulus) after exercise. Special areas in

UNIT

8.4

A thermostat on a heater uses a stimulus–response model and to keep the temperature stable. When the temperature of the room drops, the thermostat detects the change (stimulus) and turns the heater on (response). The increasing temperature is then detected (). The thermostat responds by turning off the heater. This cycle of continues, keeping the temperature almost constant.

[ Questions ]

Checkpoint Responding to stimuli 1 List six pieces of information you are currently receiving from your surroundings. 2 a Define homeostasis. b Explain why homeostasis is necessary. 3 Identify three substances in the body whose levels are controlled by homeostasis.

238

some large arteries (the receptors) detect this rise and transmit messages to the brain (the coordinating centre). Messages are then sent from the brain to various muscles (the effectors) to produce an increase in breathing rate (the response). Rapid breathing causes a decrease in blood carbon dioxide levels. This decrease is detected (the ) and the breathing rate subsequently returns to normal. Fig 8.4.2

Control of carbon dioxide levels in blood

increase in carbon dioxide level in blood stimulus

(lower carbon dioxide level)

receptor cells in main arteries

increase in breathing rate response

receptor relay by nerves

diaphragm and chest muscles

effector

the brain

relay by nerves

coordinating centre

Worksheet 8.6 Concussion in football

Stimulus–response model 4 Distinguish between a receptor and an effector, giving examples of each. 5 Match each receptor with the stimulus to which it responds. Receptor Cells of the retina Cells of the inner ear Taste buds Osmoreceptors in the brain Semicircular canals in the ear Thermoreceptors in the skin

Stimulus Gravity Chemicals Heat Light Sound Water levels

UNIT

8.4 and coordination i increase in body temperature

6 Define the following : a b coordination 7 If the carbon dioxide level in your blood was to increase after exercise, identify: a where the receptors that detected this increase would be located b the coordinating centre that would receive messages c the structures that would act as effectors d the response you would notice

viii (decrease in body temperature)

ii thermoreceptors in the skin iii

vii increase in sweating and blood flow to skin

iv hypothalamus in the brain

Think vi blood vessels and sweat glands

8 State the approximate value of the: a body temperature of a healthy human b pH level in the blood of a healthy human

Fig 8.4.3

9 Describe the most usual response to a stimulus for single-celled organisms. 10 Use the in the list below to label the diagram in Figure 8.4.3 (marked i to viii) showing control of body temperature: response, relay, , stimulus, effectors, coordinating centre, receptor, relay

v

11 Draw a diagram to illustrate the stimulus–response model that happens when you touch a hot stove. 12 List the different responses you coordinate when stepping barefoot onto hot sand at the beach.

[ Extension ] Investigate 1 The body’s homeostatic control can fail in extreme temperatures. Body temperature may rise (hyperthermia) or fall (hypothermia). a Investigate either hyperthermia or hypothermia, listing its symptoms and likely causes. b Prepare a report explaining how to avoid these two conditions. 2 A fever caused by infection may result in your body temperature rising two or three degrees above normal. Research how this happens and whether the higher temperature is beneficial or damages body cells. 3 Acidity is measured using the pH scale. a Investigate whether blood (pH 7.38) would be described as neutral, acidic or basic (alkaline). b Investigate what might cause a change in blood pH, and how the body responds to this. Fig 8.4.4

We wear less clothes in hot weather to avoid hyperthermia

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Responding

UNIT

8.4 [ Practical activities ] Sweet and salty

3 Compare the class results. Is there a difference in the taste thresholds between males and females?

Aim To identify the threshold of a stimulus Prac 1 Unit 8.4

Equipment

4 Justify the value of receptors in the body having thresholds.

12 new small paper cups, 2–3 mL each of solutions of sugar of varying concentrations (0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%), 2–3 mL each of solutions of salt (0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%), waste jar for rinsings, bottled water for rinsing mouth

5 a You knew what type of solution you were tasting. Evaluate whether this knowledge affected your judgement. b Describe how you could modify the activity to overcome any problems.

Method 1 Draw up a results table as shown here. 2 Sip the most dilute (0.001%) sugar solution. Can you taste the sugar? Record a ‘+’ in the table if you can, or a ‘0’ if you cannot.

Concentration

0.001%

0.005%

0.01%

0.05%

0.1%

0.5%

Result for sugar Result for salt

3 Spit the sample into the waste jar. 4 Repeat the test with 0.005% sugar solution. 5 Continue tasting each solution of next higher concentration until you can taste the sugar. Try the next higher concentration to be sure of your results. 6 Thoroughly rinse your mouth using the bottled water.

Sound threshold Prac 2 Unit 8.4

7 Repeat the procedure using the salt solutions, once again starting with the most dilute.

Questions

DYO

The loud tick of a mechanical clock or watch can be used to test hearing. The distance of the clock from the ear can be used as a measure of the loudness of the sound. Design an experiment to test the sound threshold for of your class. Compare the thresholds for males and females.

1 The minimum intensity that causes a response is known as the threshold for the stimulus. State your taste threshold for sweetness. 2 State your taste threshold for saltiness.

Fig 8.4.5

240

UNIT

Your nervous system controls and coordinates all parts of your body. It is the most complex of all your body systems and, despite many years of research, it is the least understood. Here is some of what we know.

Fig 8.5.1

CNS (brain and spinal cord)

The nervous system The nervous system has two parts: • the central nervous system • the peripheral nervous system. The central nervous system (CNS) is made up of the brain and spinal cord. They act as the control centre, receiving messages from all parts of the body, examining the information received, and then sending out messages to tell parts of the body what to do. The peripheral nervous system (PNS) is made up of sensory receptors and nerves. These continuously inform the CNS of changing conditions, and transmit the decisions made by the CNS back to effector organs. Messages are ed through the system by nerve cells called neurons. These are specialised cells that transmit and receive messages in the form of electrical impulses. s rosi scle iple Mult In the disease called multiple sclerosis, patches of myelin deteriorate at intervals along neurons in the CNS. The affected areas cannot conduct electrical impulses and the neurons cannot be replaced if damaged. Victims of multiple sclerosis have symptoms including loss of coordination, tremors, difficulty in seeing and partial paralysis. The cause is still a mystery, but evidence suggests that a measles-like virus may be responsible in genetically susceptible people.

The human nervous system

special

skin

organs

muscle

mo

to rve r s

ne

effectors (muscles and glands)

sen ne sory rve s

context

8. 5

Neurons

A neuron has the usual features of any cell found in an animal. It has a nucleus, cytoplasm and cell membrane, but it also has a number of other specialised parts. Around the cell body are small threads called dendrites. These make with other cells and receive information from them. There is also one long thread, the axon, which carries information away from the cell. Axons are often encased in a white fatty substance, called myelin, which insulates the axon like the plastic

large arteries and other tissues PNS (sensory receptors and nerves)

coating on an electrical wire. Myelin also enables messages to more quickly along the axon. The information is carried by electrical impulses that travel at speeds between 1 and 100 metres per second.

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Nervous control A typical neuron

cell body

Fig 8.5.2

dendrite cell membrane nucleus cytoplasm

axon

myelin sheath

nerve ending

Fig 8.5.3

Neurons are grouped together in bundles called nerves, in much the same way as an electrical cable is made up of smaller wires bound together. Some neurons, called sensory neurons, have motor neuron specialised endings sensitive only to stimuli such as heat dendrites and light. These form part of the body’s larger sense organs (eyes, ears etc.), which function by collecting different energy forms. The sensory neuron then converts this energy into an electrical impulse. In this way, cells direction of in the retina convert light impulse energy to electrical energy. Another type of neuron, the connecting neurons or axon interneurons, transfer these electrical messages within the CNS. A third type, motor neurons, transfer messages from the CNS to effector organs such as muscles.

242

A scanning electron microscope image of a neuron (light brown) showing the thick axon and several thin dendrites.

Fig 8.5.4

Two types of neurons—motor and sensory sensory neuron

cell body

axon

nucleus

myelin sheath

long distance

muscle fibres

direction of impulse

sensory receptor

The synapse Throughout the nervous system there are small gaps between neurons, called synapses. Messages cross these synapses, but not as electrical impulses. The message is carried chemically by special compounds called neurotransmitters. When an impulse reaches a synapse, neurotransmitters are released and quickly move across the gap. They move to sites on the other side, restarting the electrical impulse. The neurotransmitter is then broken down so that new messages can be received.

end of the axon of one neuron neurotransmitter

Pain relief The pain-relieving processes of acupuncture and hypnosis appear to be related to neurotransmitters called encephalins. These are the body’s own pain-deadening neurotransmitters. Acupuncture is thought to stimulate the production of encephalins. Morphine, codeine and pethidine act in much the same way as these neurotransmitters.

synaptic gap

neurotransmitter crosses the gap

dendrite of another neuron

Fig 8.5.5

Crossing a synapse

Around fifty different neurotransmitters have been identified. Many drugs and poisons affect neurotransmitters. Curare is a poison used by South American Indians on arrow tips. It blocks reception of the neurotransmitter acetylcholine, preventing messages from getting to muscles, stopping breathing and other movements. Some insecticides work by preventing the breakdown of acetylcholine, so messages are constantly received, resulting in continuous muscle spasms. Another neurotransmitter, noradrenalin, is associated with alertness. Another is dopamine, associated with emotions. Drugs such as amphetamines, cocaine and ecstasy increase production of these neurotransmitters. This results in an increased state of alertness and heightened emotions, along with high blood pressure, irritability and, later, depression and insomnia.

Pain relief using acupuncture

UNIT

8.5 Fig 8.5.6

So why do we have synapses? If neurons touched each other it would be something like turning on one switch and having every light in the house come on at once. Synapses are similar to a switchboard, allowing messages to be directed to the correct places. It is also thought that synapses in the brain play an important part in learning and memory.

The brain The brain is soft, wrinkly tissue with a mass of around 1.4 kg. Each of its twenty-five billion neurons are connected to as many as 1000 others, and there are as many as one hundred million million synapses. This huge number of neurons does not exist as a tangled mess. They form neuron networks, with neurons arranged in specific circuits. Not even the largest, most intricate computer comes close to the complexity of the human brain. It is hardly surprising then that scientists know little about what actually happens in processes such as thinking, sadness or when we try to what happened yesterday.

Don’t interrupt the flow Although the brain makes up only 2% of the body’s weight, it receives 20% of the body’s blood supply and uses 20% of its oxygen. If blood flow to the brain is interrupted, consciousness is lost rapidly and irreversible damage occurs within minutes. To avoid this, jet fighter pilots wear special pressure suits to maintain blood flow to the brain during rapid turns. The most common form of brain damage is ‘stroke’, where part of the brain is deprived of blood. This can happen if a blood vessel bursts in the brain (a haemorrhage), or more commonly when a blood clot blocks a vessel.

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Nervous control The human brain

cerebellum

ati

vis ion

on a

re a

a

r are

taste ring ci hea a ss o

oto

cerebrum (right and left hemispheres)

n

touch smell

a are

m

associa tio

Fig 8.5.7

cerebellum medulla

medulla spinal cord

The cerebrum controls many functions.

Fig 8.5.8

Protecting the brain The brain has three main structural parts: the cerebrum, cerebellum and Bumpy criminals medulla. The cerebellum In the nineteenth century controls complex muscular many scientists believed that criminals had different movements like cycling, brains to those of walking and running. The law-abiding citizens. Bumps medulla controls vital on the outside of the skull were supposed to give some activities you do not have idea of the brain and to think about, like criminal intent inside. After breathing and heartbeat. executions, death masks The cerebrum makes up were often moulded from the shaved skull as a mould. 90% of the brain’s volume. The bumps could then be It is divided into right and examined at leisure. The left hemispheres. The study of the criminal brain and skull was called surface has many folds, phrenology and is not taken creating a large surface area seriously today. with billions of neurons. These are a grey colour (hence the expression ‘using your grey matter’). The cerebrum is responsible for complex thoughts. The right side is responsible for artistic, musical, intuitive and perceptual abilities. The left takes care of language, learning mathematics and logical thinking. Some regions (the sensory areas) are concerned with receiving and interpreting impulses from sense organs. The motor areas control muscles. The association areas are concerned with memory and thinking.

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Your brain is so important that the body protects it very carefully. It is protected by the bony case of the skull and by layers of connective tissue called meninges. It also has a jacket of fluid around it called cerebrospinal fluid (CSF) to cushion against shock. The base of the brain is connected to the spinal cord. It too is protected by a bony case, the backbone, and cushioned by cerebrospinal fluid. The spinal cord transmits messages between the brain and the PNS, and controls some actions that do not require thinking.

Nervous reactions Actions that need to be carried out automatically and without thinking usually require only a few neurons, and are therefore very fast. A pathway known as a reflex arc carries these reactions (see Figure 8.5.9). For example, if you prick your finger with a pin (the stimulus), pain receptors in the skin send a message via a sensory nerve to the spinal cord. The message crosses synapses to a motor nerve which carries the message to muscles (the effector). Notice that the brain itself is not yet involved. A message may be sent to the brain, but only to keep it informed of what is happening. A secondary response might be a cry of pain. The brain may also store information so that next time you avoid touching the pin. Other reflex actions include blinking, sweating, shivering, coughing and the knee-jerk reaction.

UNIT

8.5 spinal cord sensory nerve impulses to brain vertebra

motor nerve

interneuron cell body of sensory nerve

spinal cord

pain receptors in skin

muscle

sensory nerve motor nerve

pin prick Fig 8.5.9

A reflex arc

More complex actions require messages to be sent to the brain, decisions made and responses sent back to various effectors. Some learned actions may become so automatic as to appear to be reflexes. For a nine-month-old baby, eating, especially with a spoon, requires conscious effort. As the years , pathways that control this process become so well established that the action appears to be automatic. Likewise, people who excel in sport or music perform actions with little effort after years of practice. The rest of us stumble with Prac 1 Prac 2 Prac 2 Prac 4 p. 247 p. 247 p. 247 p. 247 the task.

5 Describe the function of neurotransmitters. 6 a Explain why synapses are necessary. b State two disadvantages of synapses.

The brain 7 a Identify the three main structural parts of the brain. b State the major functions of each. 8 Label the diagram shown here, using the following words: cerebellum, medulla, spinal cord, cerebrum.

a

Worksheet 8.7 The nervous system b c

UNIT

8.5

[ Questions ]

Checkpoint The nervous system 1 a Identify the two main parts of the nervous system. b Describe what each part consists of and the main function of each. 2 Compare the neuron with other cells in the body. a How is it like other cells? b How is it different? 3 Distinguish between a neuron and a nerve. 4 Distinguish between sensory, motor and interneurons.

d

Fig 8.5.10 9 Identify which part of the brain: a you use to think b controls breathing c helps you balance while cycling d gives you sensations of touch 10 State three ways in which the brain is protected from injury.

Nervous reactions 11 Identify which of the following would be reflex actions: coughing, sneezing, reading, cycling, writing, blinking.

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Nervous control

Analyse

12 State one reflex action that occurs when: a a bright light is shone in your eyes b food enters your windpipe c you are hungry and you smell food d you spend a long time in the sun on a hot day

16 Identify which side of your cerebrum is most active in helping you answer these questions. 17 List two conscious acts that are so automatic that they may appear to be reflex actions. 18 Propose reasons why it is important that scientists continue to research the brain and nervous system.

Think 13 State the type of energy conversion carried out by each of the receptors listed. a retinal cells in the eye b cochlear cells in the ear c taste buds on the tongue d thermoreceptors in the skin 14 a Identify the type of neuron shown in Figure 8.5.11. b Identify and label parts i to v. 15 Arrange the following list of events in the correct order to describe a reflex action. Write your answer as a flow chart.

iii i


iv

v

ii

Fig 8.5.11

An impulse is sent along a sensory neuron to the brain. An impulse is sent along a motor neuron to iris muscles. A bright light is shone in the eye. Iris muscles contract, causing the pupil to narrow. Receptors detect a change in light intensity.

[ Extension ] Investigate 1 Investigate the effect of caffeine, marijuana or alcohol on the CNS and perform a role play to teach other students about your findings. 2 Research and report on one of the following disorders of the nervous system: Parkinson’s disease, Alzheimer’s disease, epilepsy. Outline the signs, symptoms and treatments for the disease you have chosen. 3 The blue-ringed octopus is one of the most deadly sea creatures. Investigate how its poison can paralyse the nervous system. 4 Investigate the differences in brain structure of humans, gorillas, dolphins and dogs.

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5 Each year, many young people seriously injure their spinal cord when they dive into water that they did not know the depth of. Many become paraplegic or quadriplegic. a Investigate what ‘quadriplegic’ and ‘paraplegic’ mean, and find the number of diving accidents in Australia last year. b Research one such case and outline factors that led to the injury (e.g. was alcohol involved?). c Report on the person’s life since the accident and their probable life in the future.

Surf Complete the following activities by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. 6 Explore interactive diagrams of the nervous system. 7 Perform a number of activities to test your reflexes.

UNIT

8.5 UNIT

8.5 [ Practical activities ] Prac 1 Unit 8.5

Memory I

Memory II

Aim To investigate how we memorise words

Aim To investigate the effect of distractions on memory

Equipment Three lists of words, each printed on separate cards (A, B and C) (note: your teacher will supply these cards—do not look at them until the activity begins), a person to act as the subject

Method 1 The subject is to read the list of words on card A until they can recall them perfectly (with no mistakes). Record the time taken to develop perfect recall. 2 Repeat the procedure using card B, then card C.

Questions 1 State which list is memorised most quickly. 2 Propose reasons why this was fastest.

Prac 2 Unit 8.5

Equipment Two stanzas of a poem, printed on separate cards, a person to act as the subject

Method 1 The subject is to read the first stanza until they can recall it perfectly (with no mistakes). Record the time taken to develop perfect recall. 2 Repeat the procedure using the second stanza, but this time make distracting noises such as singing, banging occasionally, and so on. Record the time taken to develop perfect recall.

Questions 1 Compare the times taken to learn each stanza.

3 Propose some other factors that might influence the speed at which the subject learns.

2 for any difference in the times.

4 Evaluate your results and their implications for how you should memorise material for a test.

3 Identify other factors that might influence the speed of learning. 4 Evaluate the implications of your results for where you should study.

Prac 3 Unit 8.5

Brain dissection

Questions

AIim To investigate the structure of the brain

1 Describe the surface and consistency of the cerebrum.

Equipment Lamb’s brain, dissection board, scalpel, dissecting scissors, newspapers, access to disinfectant, disposable plastic gloves

Method 1 Cover the workbench with a layer of newspaper and place the dissection board on top.

2 Explain how you could tell which was the left and right hemisphere. 3 Describe the colour and consistency of the cerebellum. 4 Describe the medulla.

2 With the edge of the scalpel, try and lift the fine membrane or skin off the brain. If successful, peel it off. 3 When using the scalpel, make many light cuts instead of one deep cut. When cutting, always draw the scalpel away from your hands.

Response time Prac 4 Unit 8.5

4 Separate the right and left hemispheres of the brain and remove the cerebellum and medulla. 5 When completed, wrap all material in the newspaper. Your teacher will tell you what to do with dirty equipment.

DYO

Design an experiment to measure the time taken to respond to either a visual or an auditory stimulus. For example, measure the time taken for your blindfolded partner to press a buzzer in response to the sound of a bell. Alternatively, drop a ball from a given height and measure how far it falls before your partner catches it. Determine whether repetition of the task reduces the time taken. Suggest reasons for any variations observed.

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UNIT

context

8.6 The endocrine system uses chemical messages called hormones to transfer information around the body. These hormones are responsible for controlling many changes that occur in our bodies, most notably those that occur during puberty. Hormones also control many other processes in our bodies such as the storage and release of glucose into the blood. Even plants use hormones to send messages. They are a very important part of our chemistry.

Fig 8.6.1

Major human endocrine glands

pituitary

thyroid

adrenal

ovary (females only)

testis (males only)

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Hormones and how they work Hormones are produced by the endocrine glands, which are scattered throughout your body. Although they may work together, they are not controlled from one central location like the nervous system is. Hormones regulate functions like growth and development, water balance, sexual reproduction and the rate of chemical reactions in cells (see the table on the next page). Although hormones travel to all parts of the body, only particular target cells respond to a particular hormone. Other cells are ‘blind’ to the hormone. How do hormones know which is the target cell? A hormone has a specific shape that fits chemically into a receptor on the target cell’s membrane. This is like placing pieces in a jigsaw puzzle, as shown in Figure 8.6.2. The bonding of the hormone to the receptor starts changes in the cell’s activities. It can be difficult to extract and isolate hormones because they are only secreted in very small quantities. The concentration of hormones in pancreas the blood is very low, about equal to dissolving a sugar cube in a swimming pool. When hormones through the liver they are broken down and converted to relatively inactive substances, which are excreted by the kidneys. One test for pregnancy involves measuring the levels of these hormonal breakdown products in urine.

Name of gland or organ where the gland is found

Names of some of the hormones produced

Adrenals

Adrenalin

Ovaries

Oestrogen Progesterone

Pancreas

Insulin and glucagon

Pituitary

Growth hormone (HGH) Antidiuretic hormone (ADH) Stimulating hormones

Thyroid

Thyroxin

Testes

Testosterone

secretes

travels in blood to hormone

endocrine gland

receptor on target cell

target cell change in cell activity hormone-receptor

Fig 8.6.2

The action of hormones

Why hormones? Why does the body use hormones as messengers as well as nervous impulses? Nerve transmissions are very fast. Circulation of hormones takes time. It can

Functions controlled by the hormone Readiness or flight or fight Female sexual development and the menstrual cycle Control of ovary and uterus in pregnancy Blood glucose levels Cell growth and development Water balance Direct other glands to release hormones Rate of chemical reactions in cells Male sexual development and sexual activity

take minutes, hours or even days for the level of a hormone in blood to reach a peak. Concentrations are small, but when the hormone affects a cell, the effect is usually relatively long lasting. This reduces the amount of hormone needed. Hormones provide an ideal mechanism for control of widespread and longterm activities. Often a response to a stimulus will involve both systems. The nervous system sends a rapid response when you are frightened. Messages are transferred swiftly along neurons, reaching an effector to cause an almost immediate and brief reaction. The endocrine system also responds, but more slowly and over a longer period. Adrenalin (known as the fight-or-flight hormone) is released from the adrenal glands and causes various effects. The heart beats faster, breathing rate increases, blood is diverted to the muscles, pupils dilate, hairs on the skin stand on end and the brain becomes more alert. Your heart pounds and you get that sinking feeling Fast and slow control

The nervous system provides rapid messages.

UNIT

8.6

Fig 8.6.3

Hormones provide slower messages.

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Chemical control in your stomach. The overall effect is to boost the speed of your reaction to the fright.

Controlling growth Hormones control longer-term activities like reproduction, growth and development. One gland, the pituitary, plays an important part in controlling growth. It not only releases hormones that directly affect target cells, but also instructs many other glands to release their hormones. The pituitary receives messages directly from the hypothalamus in the brain and thus provides a vital link between the nervous and endocrine systems. One sequence of events involves the hypothalamus, pituitary and thyroid glands. Under instruction from the hypothalamus, the pituitary releases thyroid-stimulating hormone (TSH). This causes the thyroid gland to release thyroxin. Thyroxin controls the speed of cell reactions and therefore influences growth. A deficiency of thyroxin in Fig 8.6.4

The pea-sized pituitary gland is located at the base of the brain.

infancy results in cretinism, or stunted physical and mental growth. This can be cured in its early stages by istering thyroxin.

The pituitary is the ‘master’ gland.

hypothalamus

ting stimula thyroid H) ne (TS hormo

ado gon

kidney

gr

ow (H th h G H orm ) o

ne

other organs e.g. mammary glands

testis

ovary

250

an

rmones

go

trop ic h

r

ot

d na

ch

m

other ho

orm

rm

o

i op

hu

one s

s

thyroid

one

antidiuretic horm (ADH)

pituitary

e on

Fig 8.6.5

bones

Fig 8.6.6

UNIT

8.6 Thyroxin released from the thyroid gland influences growth.

hypothalamus pituitary receives a message from the hypothalamus

thyroid-stimulating hormone (TSH)

stops TSH production ()

thyroid gland thyroxin produced controls chemical reactions in cells

Fig 8.6.8

Gigantism and dwarfism can result from abnormal levels of HGH. Some giants have grown to over 2.7 m tall, while dwarfs may be less than 0.6 m tall.

Controlling glucose levels

Fig 8.6.7

Goitre results from iodine deficiency.

Goitre Iodine is an essential component of thyroxin. A deficiency of iodine can cause enlargement of the thyroid gland (a goitre). Goitres were once common in areas where the soil lacked iodine, but use of iodised salt has largely solved this problem.

Another hormone produced by the pituitary is human growth hormone (HGH), which influences total body growth. Lack of HGH in childhood can lead to dwarfism. Though small, these people have normal intelligence and are well proportioned. If diagnosed early, injections of HGH can be given to children suffering from lack of HGH. Too much HGH in childhood leads to gigantism, producing an abnormally tall person.

Many substances must be kept at a constant level within the body. Cells need a continuous supply of glucose to produce energy, and inadequate levels may result in low energy and possible cell death. Blood glucose levels are usually maintained in a very narrow range Too much or too little? by the action of two hormones, Insulin-dependent diabetics must obtain a regular supply insulin and glucagon, both of insulin. They must also produced by the pancreas (found eat regularly. If a diabetic just below your stomach). injects a dose of insulin (which lowers blood glucose If blood glucose levels increase, levels) but then does not eat for example after eating chocolate, later, their blood glucose insulin is released. This stimulates will fall too far. The brain storage of glucose in the liver, and will be affected, resulting in a hypoglycaemic (low sugar) increases uptake and use of episode or ‘hypo’, and glucose by cells. Blood glucose possible unconsciousness. levels then drop, inhibiting To avoid this problem, many diabetics wear an identifying further release of insulin. label and carry a sugar Glucagon works in a similar way. source (like jelly beans) that In response to low blood glucose can be taken if signs of a levels it directs the liver and cells ‘hypo’ appear. to release glucose.

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Chemical control Fig 8.6.9

• Type II, or non-insulin-dependent diabetics, do not produce enough insulin, or have cells that do not respond correctly to insulin. Treatment involves a special diet, an exercise program, use of drugs and possibly insulin injections.

Control of blood glucose Choc-N

ut Bar

food eaten blood glucose level falls

rising blood glucose stimulus

Worksheet 8.8 Diabetes type I Worksheet 8.9 Hormonal control of the menstrual cycle

glucose removed for storage response

pancreas receptor

Pheromones

insulin released into blood hormonal relay

liver effector

Approximately one million people in Australia suffer from diabetes mellitus, a disease in which blood glucose levels are not maintained within the required range. There are two basic types of diabetics. • Type I, or insulin-dependent diabetics (around 15% of cases), have a defective pancreas. High blood glucose levels result because the pancreas does not produce enough insulin. This may result in glucose in the urine as the body tries to rid itself of its excess. Long-term effects of excess glucose include damage to vital organs such as the kidneys. Treatment involves the use of daily insulin injections.

Hormones are not the only chemicals that influence the behaviour of animals. Chemicals called pheromones may also dramatically affect behaviour. Many insects use pheromones to attract mates. of the opposite sex can detect pheromones in the air several kilometres away. These chemicals are effective in very small amounts. The female silk moth carries enough pheromones in her abdomen to stimulate more than one billion males! These sexattractant pheromones act on the CNS, producing immediate behavioural changes. Other types of pheromones act more slowly, affecting growth and development. Termite queens use Aiming high pheromones to stop larvae It has been suggested developing into new queens. that dogs can judge the size and therefore the Ants use pheromones to mark potential danger of food trails. Use of pheromones another dog by the is not restricted to insects. height at which its urine Much information is conveyed has been sprayed up a tree. It has also been by larger animals with the suggested that dogs scent of pheromones. Dogs and wanting to create a more possums use these smells frightening impression try to aim as high when marking out their as possible! territories by spraying urine.

Plant hormones

Type I diabetics require regular insulin injections.

252

Fig 8.6.10

Plants also produce hormones. These regulate growth, flowering, fruit production and ripening, and seed germination. A series of experiments by Darwin, Boysen-Jensen and Went in the early 1900s showed that certain plant responses were due to chemicals. A response where a plant grows towards or away from a stimulus is called a tropism. Darwin and others investigated phototropism (growth towards light), and showed that chemicals (hormones) were

responsible for the plant’s response to light. Some of the experiments used are illustrated in Figure 8.6.11.

The action of auxin in phototropism

Prac 1 p. 255

Prac 2 p. 255

tip removed foil light

When covered with foil or with tip removed no bending occurs.

UNIT

8.6 Fig 8.6.12

auxin is made here

auxin diffuses down the shoot concentrating on the shady side cells elongate more due to auxin

tip did not bend light mica (a thin crystal) When diffusion of chemicals is stopped by mica no bending occurs. tip bent light

agar (a type of jelly)

When diffusion of chemicals via agar is allowed bending occurs.

Fig 8.6.11

Experiments examining phototropism

Selective killers Hormones can be used as selective weedkillers. These hormones affect broad-leafed plants (the weeds), but not narrow-leafed plants (the grasses). Herbicides 2,4-D and 2,4,5-T are chemically similar to auxins, but have chlorine added. 2,4,5-T was an active component of the Agent Orange defoliant used during the Vietnam War.

How do hormones bring about phototropism? The tips of growing shoots produce hormones. They then backwards from the tip, stimulating cells to elongate. If the shoot is exposed to light from one side, on the exposed side the hormone is destroyed. Hormone concentration on the shady side is therefore greater. The cells here elongate more rapidly, causing bending towards the light. The particular hormone causing this response is one of a group of hormones known as auxins.

Auxins are not the only plant hormones. Other plant hormones include the gibberellins, which control plant growth and have a role in fruit development and seed germination. The dramatic effect of these hormones is seen in the growth of the seeds in Figure 8.6.13. The plant treated with gibberellins grew dramatically compared with the untreated seed.

Rapid responses Some rapid responses shown by plants, like the closing of the Venus flytrap, are not due to hormones. These responses are due to specialised cells, called turgor cells. If these sensitive turgor cells are irritated they collapse, causing the plant to move.

The dramatic effect of one plant hormone

Fig 8.6.13

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Chemical control

UNIT

8.6

[ Questions ]

Checkpoint Hormones and how they work 1 a Describe what hormones are. b State where they are produced. c Describe how they are transported. 2 Outline how hormones recognise their target cells. 3 Match each endocrine gland to the hormone it produces: Gland Adrenal Pancreas Pituitary Thyroid Ovaries Testes

Hormone Oestrogen Adrenalin Testosterone Insulin ADH Thyroxin

15 The diagram shows several endocrine glands labelled using the letters K to P. Identify (using the letters K to P) which gland produces a hormone that controls: a b c d e f

blood glucose levels female reproductive functions rates of chemical reactions in cells water levels within the body readiness of the body for action deepening of the male voice at puberty

K

Why hormones?

L

4 Listed below are several symptoms of stress caused by the release of adrenalin. Explain how each plays a role in preparing the body for action when stressed. increased heart rate, dilation of bronchioles, glucose release from the liver, increased breathing rate 5 Describe a situation in which the response of the body is controlled by both the nervous and endocrine systems.

N

M

Controlling growth 6 Identify which endocrine gland could be called the ‘master’ gland. Explain why. 7 Outline the hormones involved in growth and their effect on the body.

Controlling glucose levels

O P

8 Using Figure 8.6.9 as a guide, draw a flow chart to show the body’s response to a decrease in blood glucose levels. 9 Describe the causes of diabetes.

Pheromones Fig 8.6.14

10 Distinguish between a pheromone and a hormone. 11 Identify two examples of pheromones and describe their effects.

Plant hormones 12 Explain why plants need to detect and respond to: a light b gravity 13 A plant will grow towards a light source. Explain how the hormones known as auxins cause this.

Think 14 Explain what prevents a hormonal response from continuing long after the hormone has been released.

254

16 State two reasons why the body would use hormones rather than electrical impulses to send messages.

Analyse 17 Construct a table to compare the nervous and endocrine systems. Your table should include comparisons of the nature of the message produced, how the message is distributed, speed of delivery and length of response produced. 18 State the type of plant response likely to be involved in: a heliotropism b hydrotropism

UNIT

8.6 [ Extension ] Investigate 1 Investigate more about diabetes, including: a how the insulin used by diabetics is obtained b treatments for insulin-dependent diabetics that would eliminate the need for daily insulin injections 2 Explain the role of hormones in controlling the female reproductive cycle. How is this system of control used in the various contraceptive pills? 3 Examine the role of juvenile hormone in the moulting and metamorphosis of insects. How might knowledge of this hormone be used to control insect pests?

5 Investigate one commercial use of plant hormones, such as the use of gibberellins on grapes and in the brewing industry, the use of auxin as a rooting hormone in plant propagation, or the use of hormones to produce flowers at the ‘wrong’ time of year.

Surf 6 Explore interactive diagrams of the endocrine system by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button.

4 Investigate one commercial use of pheromones—for example, the control of oriental fruit moth, a major pest of peach trees in Australia.

UNIT

8.6

[ Practical activities ] Plant tropism Aim To investigate tropism in plants

Prac 1 Unit 8.6

Tradescantia shoot

Equipment 6 shoots of the plant Tradescantia (commonly known as wandering jew), 6 test tubes, melted paraffin wax, water, a darkened area and a well-lit area to place plants

water

Method 1 Place one shoot in each of the six test tubes, add water and seal them with paraffin wax.

test tube sealed with paraffin wax

2 Set up three test tubes as shown in Figure 8.6.15, and place them in a well-lit area. 3 Set up another three test tubes as shown in Figure 8.6.15, and place them in a darkened area. 4 Observe any changes in the plants after two hours.

Questions 1 Sketch the shoots in the six test tubes after two hours. 2 What type of tropism is shown in the experiment? Explain your answer.

Fig 8.6.15

3 Explain why it was necessary to place the tubes in both light and dark.

Investigation of a plant tropism

Plants and gravity Prac 2 Unit 8.6

DYO

Design an experiment to investigate the response of plant roots to gravity.

255

Science focus: Remote sensing Prescribed focus area: The nature and practice of science Our limited senses The human senses are amazing things that we use to detect and respond to the environment around us. Imagine trying to survive without them! But humans are limited in the observations and measurements they can make. We can only see so far, and hear sounds to a certain level. There are many things that we cannot detect, and many other things we would detect if we could be in the right place at the right time. But we can only spend limited time in some environments, such as space, before we have to return.

Enhancing our ability to sense Remote sensing allows us to detect many things our own senses cannot. It also allows us to collect data from many places and in many ways that were previously impossible, and to do this with great accuracy over long periods of time. The dramatic increase in the processing power and speed of computers has also enabled us to process information at speeds no human could ever hope to achieve manually. Most scientists now use data logging to collect and analyse their experimental results. This involves using specialised sensors and probes that transmit the information collected to a computer. The data logger may be a simple device such as the types used in schools, or very complex, such as those found on satellites. Data loggers are now common, because of their speed, accuracy, ability to work for long periods, and ability to detect what our senses cannot.

Using electromagnetic waves The electromagnetic spectrum consists of waves of electric and magnetic fields. These waves all travel at the speed of light (300 000 km per second). Humans have specialised sensors—our eyes—to collect the visible wavelengths of electromagnetic radiation. Scientists have used their knowledge of how electromagnetic waves travel through different materials to design a whole range of probes and sensors. These sensors can detect particular

256

Data logging is being used here to collect information on locomotion. The patient is wearing infra-red reflective markers and being monitored by infra-red cameras. The data will be used to model how the patient walks, and this information will help to assess leg and foot injuries or implanted ts.

Fig SF8.1

electromagnetic waves that our eyes cannot, and hence explore things that were previously impossible. Sensors can now detect most of the invisible electromagnetic waves. Remote sensing can be either ive or active. ive remote sensing detects available (background) electromagnetic energy from natural sources (such as sunlight). In active remote sensing, an artificial source of electromagnetic radiation (such as radar) is used to ‘illuminate’ the scene. Remote sensing of different electromagnetic waves coming from space has provided scientists with huge amounts of information about the universe. Many remote sensing probes have also been sent into space to collect data.

Fig SF8.2

The electromagnetic spectrum, showing the different bands of electromagnetic waves

Wavelength in metres (m) 10–12 10–11 10–10 10–9 1 pico1 nanometre (pm) metre (nm) gamma rays

X-rays

1020 1019 1018 Frequency in hertz (Hz)

10–8

10–7

ultraviolet rays

1017

1016

1015

10–6 10–5 1 micrometre (µm)

10–2 10–3 1 millimetre (mm)

infrared rays

visible light

1014

10–4

1013

1012

10–1

microwaves

1011

1010

101 1 metre (m)

102

radio waves

AM radio FM radio short-wave long-wave radio radio 109 108 107 106 105 1 gigahertz 1 megahertz (GHz) (GHz)

MRI uses electromagnetic waves to look inside the body and detect disease such as these brain tumours.

‘The dish’ at Parkes ively collects radio waves from space.

103 105 1 kilometre (km)

Fig SF8.4

Fig SF8.3

Medicine has adapted remote sensing techniques to see inside the body. X-rays have been used for a long time, but more sophisticated techniques like MRI (magnetic resonance imaging) allow us to see even more detail inside the body. With probes and sensors now often mounted on satellites and aeroplanes, remote sensing is proving invaluable in studying and monitoring the Earth’s features, including: • weather patterns • temperature of the Earth and oceans

• shape of the land surface • penetrating the oceans and ice to reveal details of the sea floor • natural phenomena such as bushfires and volcanos • vegetation in agriculture and forestry • the ozone hole • tracking animals

257

• monitoring pollution, algal blooms and oil spills in lakes and oceans • navigation • spying on other countries. This information is used for things such as weather forecasting, scientific research and by the military.

Other remote-sensing applications

This NASA satellite is known as the multi-angle imaging spectroradiometer (MISR). It collects data about the Earth’s climate and atmosphere by measuring reflected sunlight.

Fig SF8.5

Apart from electromagnetic waves, scientists have designed very sensitive probes to measure many important features of the Earth’s surface and to explore what might be found below the surface. As well as satellites, remote sensing can be carried out from aeroplanes to collect information for particular locations. With very sensitive sensors that can detect changes in the Earth’s gravity, a survey of how the Airborne and satellite remote sensing allow us to study many features of the Earth.

258

Fig SF8.6

[ Student activities ] 1 a In small groups discuss reasons why science has begun to rely more on technology to collect data. b List examples of situations where humans would not be able to directly make measurements themselves. c Describe some of the technological tools that are used to assist scientists in their work in each situation you listed for part b. 2 Research the different bands in the electromagnetic spectrum shown in Figure SF8.2 and construct a table to show different types of electromagnetic waves and if/how they are used in remote sensing. 3 Remote sensing is providing enormous amounts of very useful information. This remotely sensed computer-generated image of the Earth is based on satellite data. It shows water (blue), bare land (brown) and vegetation (green). The ocean floor topography is shown by different shades of blue.

Fig SF8.7

gravity in the area changes can reveal important detail on the composition of the underlying rocks. This form of survey has been particularly useful to archaeologists, who can now easily find denser rocky objects indicating tombs and buildings that lie buried below the sands. Geologists can also identify locations where mineral deposits may occur. Another very useful technique is a ‘seismic survey’. In this technique a small explosion, or a series of explosions, is set off in a particular location. A regular array of sensors is placed around the region to collect information on the vibrations of the Earth’s surface, known as seismic waves, produced by the explosion. By combining the information from the sensors using a computer, the nature of the rocks under the surface can be predicted. This is of particular use in mining to locate valuable deposits of minerals including oil and natural gas. Sensing and analysing the seismic waves produced by earthquakes has played an important part in allowing scientists to create a model of the internal structure of the Earth. Sound is also used in remote sensing—examples are ultrasound in medicine (see Chapter 6) and fish finders for commercial and recreational fishing.

a Research remote sensing and choose one example that is proving useful. You may choose one of the examples covered in the text or find another. b Produce a poster to explain how the remote sensing is done and how the information obtained is used. 4 a Evaluate the usefulness of remote sensing to the scientific and general community. b Describe some examples of remote sensing to your evaluation. 5 a Design and carry out an experiment that uses data logging equipment to collect and analyse information. A simple experiment like measuring DYO the cooling curve of water may be suitable. b Perform the same experiment using traditional techniques. c Compare the different methods to see which was easiest, fastest, most reliable (produces less errors).. 6 Think of a new application for remote sensing. a Outline this new use for remote sensing. b Discuss why this application would be beneficial. c Design a remote sensing probe for your new application.

259

>>> Chapter review [ Summary questions ] 1 Copy and label the diagram of the eye shown here.

2 Describe the function of each of the following parts of the eye: iris, lens, retina, choroid. 3 a Identify the three main regions of the ear. b State what each is filled with. 4 Describe the function of each of the following parts of the ear: eardrum, ossicles, semicircular canals. 5 List as many sense organs as you can. 6 Draw a diagram of a section of skin to demonstrate as many features as you can. 7 Identify the parts of the tongue that detect sour tastes. 8 Explain in a sentence what happens when we smell something. 9 Copy and label the diagram of the ear shown below.

260

10 a State two reasons why organisms need to be responsive to their surroundings. b Explain why response to a stimulus often requires coordination. c Identify the two systems of coordination in humans.

21 Glucose levels in your blood are carefully controlled so they remain within certain limits. a State the name of this careful control. b Explain why it is necessary to control blood glucose levels. c Identify which coordinating system (nervous or endocrine) is most involved in controlling glucose levels. d Identify the name of the condition in which this control is defective.

11 Demonstrate, using examples, what is meant by: a b c d

a stimulus an effector a receptor a response

22 Determine whether the following statements about the endocrine system are true or false: a Chemicals are used to deliver messages. b Messages are ed along neurons. c Messages are delivered more slowly than in the nervous system. d Responses to stimuli are rapid. e Activities are controlled from one central location.

12 a Identify four stimuli to which you respond. b State the type and location of the receptors that detect these stimuli. 13 Draw a labelled diagram to illustrate the structure of a typical neuron. 14 Match the parts of the brain to the functions listed: Part Cerebellum Medulla Meninges Cerebrum

Function Controls involuntary actions such as breathing Centre for sight, hearing and speech Controls muscle movements while you are cycling Protect the brain from injury

23 Match the hormones to the functions they control: Functions Blood glucose levels Female reproductive functions The rate of chemical reactions in cells Water levels within the body Readiness of the body for action Deepening of the male voice at puberty

15 Neurons do not touch each other. They have small gaps between them. a State the name of these small gaps. b Describe how neural messages cross these small gaps.

[ Interpreting questions ]

16 a Clarify what is meant by a reflex action. b Identify three of your own reflex actions. c Explain why reflex actions need to be very fast and how they achieve these speeds.

24 a Identify the type of neuron (sensory, motor or interneuron) shown in the diagram. b Explain your choice.

17 a State three activities in humans that are controlled by hormones. b State three activities in plants that are controlled by hormones.

[ Thinking questions ]

axon

18 A pupil will dilate under certain conditions. Explain why and when this would occur. 19 Describe a condition of the eye (e.g. myopia) and how it can be corrected. 20 Describe how you could reduce the sensation of taking an unpleasant medicine.

Hormones ADH Testosterone Insulin Oestrogen Thyroxin Adrenalin

cell body


long distance nucleus

>>

261

>>> 25 A simple diagram of the CNS is shown below, labelled A to D.

27 The diagram below shows control of glucose levels in the body. Complete the missing labels a to f.

Use these letters to identify which part: a b c d

is the centre for decision making controls the heartbeat transmits messages from the PNS to the brain receives and interprets messages from the eyes and ears

rise in blood glucose levels stimulus a releases b

blood glucose level falls f

b transported via c

A glucose removed for storage e

d effector

B C D

26 The diagram below shows the reflex arc for what happens when your knee is struck lightly with a hammer. Use the following to label the diagram: response, stimulus, sensory, nerve, motor, nerve, receptor, effector.

knee is struck i muscle contracts to move lower leg vi

stretch receptors ii

28 a Define ‘tropism’. b Describe two examples of tropisms. 29 Evaluate the importance of our senses. How would we survive without one or all of them? 30 a Outline 3 uses of remote sensing. b Describe why remote sensing can do things that our senses cannot. c Discuss the applications and importance of remote sensing to society. d Evaluate the importance of satelites to society and the environment. e Describe an example where data logging would be useful. Worksheet 8.10 Sense and control wordfind

relay via iii

Worksheet 8.11 The senses crossword leg muscle v relay via iv

262

Worksheet 8.12 Sci-words spinal cord

>>>

9

Simple machine technology

Key focus area

>>> The applications and uses of science

calculate the mechanical advantage of some simple machines explain some uses and advantages of levers, pulleys, wheels, axles, gears and inclined planes

Outcomes

describe simple technologies and machines that make tasks easier

5.1.2

By the end of this chapter you should be able to:

describe examples of complex machines and their applications describe some Aboriginal technologies and their application to everyday life.

your house that make jobs easier for you.

3 What can humans physically do now that could not be done 100 years ago?

4 What do you think is the most important invention in the history of humankind? Give reasons for your choice.

5 Name an Aboriginal technology and describe what it is used for.

Pre quiz

1 How do aircraft stay in the air? 2 Make a list of machines around

>>>

UNIT

context

9.1 Even before written records began, humans were using the technology of their time to help them hunt for food, build shelters and make life easier. The simple technologies of the ramp, wedge, screw, lever, wheel and pulley were some of the first and most useful devices ever invented. It is these technologies that helped lift the huge pillars and blocks of stone to build the temples and pyramids of the ancient Egyptians, Romans and Greeks. They also helped them to draw water from wells and travel faster than ever before. These simple technologies are useful enough to

Let’s say a certain job takes 12 joules to do. We could do the job in a number of ways:

Energy needed to do the job (J)

Effort force Distance we needed to do need to move to the job (N) do the job (m)

Proof that this will do the job

Work in science

12

12

1

12 x 1 = 12

Simple technologies and the machines that use them are all about force. They generally reduce the amount of effort required, making a job much easier. Sometimes they allow us to move bigger objects than would normally be possible. Effort is the force you need to apply to move an object. The object and its weight are called the load. The word ‘work’ is used in many ways. ‘Hard work’, ‘a lot of work’ and ‘homework’ are expressions we hear every day. Scientists mean something very different by the word ‘work’, however. To understand how simple technologies and machines make a job easier we need to understand the scientific meaning of work. Scientifically, work is the energy needed to move something over a certain distance. Like all energy, work is measured in joules (J).

12

6

2

6 x 2 = 12

12

4

3

4 x 3 = 12

12

3

4

3 x 4 = 12

12

2

6

2 x 6 = 12

12

1

12

1 x 12 = 12

moved in doing the job

work = effort force x distance

needed to get the job done

Some simple mathematics will help us understand what’s happening here.

264

be used on their own. By themselves, each is a simple machine. Complex machines are formed when different technologies are combined. Most machines around us today, from eggbeaters and staplers to a bike gears are complex machines that use multiple technologies.

What this all means is that if the distance we move is greater, the effort we need to put in is less. All simple technologies use this fact to make them effective.

The inclined plane A ramp (sometimes called an inclined plane) is one of the oldest and simplest technologies. It is used when we need to get a heavy object up to a higher level. If you want to lift a load, you need to do a certain amount of work regardless of how you go about it. The work will depend on the weight of the object and the height you lift it, not on how you do it. Imagine you’re helping your family to move house and need to load the refrigerator onto a truck. The shortest path onto the truck is straight up, vertically. This is going to be very difficult (perhaps impossible)

since it requires you to put in an effort force at least equal to the weight of the fridge. Yet if you pull or push the refrigerator up a ramp, you will find the job easier. Although the work is the same, less effort is required because you are moving the fridge a greater distance.

less effort full effort

e

rfac

su ing

slop

Fig 9.1.1

Effort is less when distance is more.

Mechanical advantage Mechanical advantage measures how effective the technology or machine is, and can be calculated by dividing the load you want to move by the effort you need to put in.

Wedges An escalator can be thought of as a moving ramp. So can a wedge. A wedge is simply an inclined plane that moves through another object, forcing apart or splitting the object as it does so. An axe or wood splitter is an obvious wedge. It reduces the effort needed to split a log by forcing the wood to travel up the long edge of the blade. The sharper the blade, the longer the edge and the less effort required to split the timber. Knives and our front teeth (the incisors) also act in this way, making it easier Zip! Coincidence in science to cut and slice through sometimes means that food. two people on opposite The zip fastener is an sides of the world have example of a twentieththe same idea or invent the same contraption at century technology that uses exactly the same time. three wedges. The zipper’s The modern, successful slide contains wedges that zipper was invented in 1911 by Catharina turn a little effort into a Kuhn-Moos and strong force that opens and Henri Foster, neither of closes the fastener. Without whom knew about the other or what they were this assistance, the teeth of working on. the zip are nearly impossible to or part. A zipper uses three wedges.

UNIT

9 .1

Fig 9.1.2

Mechanical advantage = load/effort

For example, if a simple machine lifted a 60 N weight (this is about 6 kg) but an effort of only 20 N was required, the mechanical advantage would be: mechanical advantage = load/effort = 60/20 = 3

Better machines have larger mechanical advantages, so better machines than this one would be able to either: • lift a bigger load (say, 600 N) with the same effort (20 N). This would give a larger mechanical advantage: load/effort = 600/20 = 30 or • lift the same load as before (60 N) but with a lot less effort than before (say, 2 N): mechanical advantage = 60/2 = 30 The better the machine, the larger the mechanical advantage. Prac 1 p. 267

Prac 2 p. 268

265

>>>

The ramp Screws, nuts and bolts A screw is like a wedge in that it is also a ramp, this time spiralling around a metal cylinder. Screws also penetrate materials such as: • solids—woodscrews are screwed into timber • liquids such as water— a propeller on a boat is The Archimedes a screw screw • gases such as air— Archimedes (287–212 BC) propellers on an aircraft, is usually ed for his alleged naked dash or an electric fan. from his bath and through Try to hammer a the streets after he solved woodscrew into a piece of the problem of buoyancy. His fame in ancient timber and you won’t get e was, however, as a Greec very far. It would need an scientist, mathematician, extremely large force to do so. philosopher and inventor. Yet if the screw is turned, the One of his inventions still in use today is the timber is moved along the Archimedes screw, a spiral ramp. Because of the device originally used to great distance covered, a much bail out the hulls of warships but now smaller force is required, commonly used to raise although a lot of turning has from dams and rivers

to be done. Once again, distance is increased, so the effort is less. A bolt and its nut work the same way, although in this case the nut is wound down the screw of the bolt.

effort turning screw

wood screw

force on wood

A screw is just a curved ramp.

water in the Middle East.

Fig 9.1.3

Worksheet 9.1 History of ramps

UNIT

9.1

[ Questions ]

Checkpoint Work in science

9 List five examples of where wedges are used to more easily separate or split an object.

1 Define the term ‘work’ when used in the scientific sense.

Screws, nuts and bolts

2 Clarify whether work is energy or a force.

10 Describe how a screw is really just a ramp.

3 Identify the unit normally used for work.

11 Outline three uses of screws.

The inclined plane 4 Copy and complete: A ramp reduces effort by increasing ________. 5 List five examples of ramps being used to make a job easier.

Think 12 Explain why a path zigzagging up a mountain is easier to walk than a track straight up to the top.

7 Define ‘mechanical advantage’.

13 Calculate the mechanical advantage. a load = 12 N, effort = 6 N b load = 18 N, effort = 6 N c effort = 3 N, load = 18 N d load = 5 kg (about 50 N weight force), effort = 10 N

8 Assess whether a machine with a high or low mechanical advantage is better.

14 Determine which of a, b, c or d in Question 13 is the best machine.

6 Construct a rule about how ramps make the job of lifting a load easier.

Mechanical advantage

266

Wedges

15 Construct a table to summarise simple machines that use ramps, such as the screw or wedge. For each machine outline briefly how it makes doing a job easier.

UNIT

9 .1 [ Extension ] Investigate Analyse 16 Twenty-four joules of work was needed to lift an object up to a certain height. Sarah measured its weight with a spring balance and found it to be 24 N. Calculate the load force that Sarah was trying to lift. 17 Sarah then thought about the ramp that would do the job most easily and constructed the following table to help her. Copy and complete her table. Work (J)

Ramp length (m)

Effort needed (N)

Proof that this will do the job


24

1

24

1 x 24 = 24

24/24 = 1

24

2

24 24

2 x 12 = 24 8

24/8 = 3

4

24 24

6 x 4 = 24

24/4 = 6

1 a Record as a series of diary entries all the ramps that you use in one day. b For each ramp used describe how it made your day easier. c Design a ramp that would have made something you did during the day easier. Try to design something unusual, not just replacing stairs with a ramp, for example. 2 a Investigate the design of the Archimedes water screw and draw a diagram to show how it works. b Construct a working model of this technology.

8

24 24

18 Which ramp would make the job easiest for Sarah? Explain.

UNIT

9.1

[ Practical activities ] Ramps

Method

Aim To investigate the relationship between the Prac 1 Unit 9.1

slope of a ramp and effort

1 Make a pile of textbooks on your desk about 10 cm high. 2 Construct a table or spreadsheet as shown below.

Equipment

Spring balance, ramp, dynamics cart and wooden block, small masses, sticky tape, books, protractor

3 Weigh the dynamics cart and the block of wood with a spring balance. Tape masses on them until both are about the same weight. Record their new weights.

>> Angle (°)

Distance along Effort to move ramp (cm) cart (N)


Effort to move block (N)


267

>>>

The ramp

spring balance spring balance block

trolley trolley

books 10 cm 0 12

110

100 90 80 70

60 50

40 30

10 0

180 170 16

20

0 15 0 14 0

0 13

protractor

tape masses to make block about the same weight as trolley

spring balance block 110

50

20

0 15

60

30

10 0

180 170 16

100 90 80 70

40

0 14 0

0 13

0 12

protractor

Fig 9.1.4

Testing a ramp

4 Slowly lift the cart vertically up until it reaches the top of the stack. Record the effort required from the spring balance.

Ramps for the disabled

5 Repeat with the block. 6 Now place the ramp on the books so that its angle with the desk is very small.

Prac 2 Unit 9.1

7 Measure the angle with a protractor and measure the distance along the ramp from the bottom to the top of the books. Record it. 8 Drag the cart up the slope with the spring balance until it reaches the top of the books once more. Record the effort needed, then repeat with the block. 9 Try three different angles. You might need to overhang the books to do so. Take angle and effort measurements each time for both the cart and the block.

Questions 1 The work required to drag the cart and block up was the same in each case. Explain why. 2 Describe what happened to the effort force needed as the ramp got longer. 3 Which was the better ramp? Explain. 4 Which was easier to get up the slope—the block or the cart? Propose reasons for your answer.

268

DYO

Disabled ramps must be constructed with a slope of no more than 1:14 for ramps over 1250 mm long and 1:8 for ramps less than 1250 mm long.

Aim To test commonly used ramps to determine whether they comply with the requirements of the disabled

Method 1 Find ramps around the school, at the shops or at home and take appropriate measurements to find their slope. 2 Carry out appropriate calculations and compare their slopes with those needed by the disabled.

Questions 1 Propose why shorter ramps are allowed to be steeper than longer ramps for the disabled. 2 Did the ramps you checked comply with the regulations?

UNIT

9.2 context

Ancient propaganda?

The lever is an old technology that can be dated back about 5000 years. You use many different forms of levers every day, such as a shovel, a spoon or a tennis racket. A lever can be any solid object that is made to turn round a pivot or fulcrum. A load is placed somewhere along the lever and an effort causes the turning. Generally, levers are force multipliers: we put in a small effort and the lever system multiplies it so that we can lift much heavier loads. As with ramps, levers reduce the effort needed to lift a load. Once again the disadvantage is distance: the more we wish to reduce effort, the further we need to move the lever.

5000-year-old Egyptian The oldest diagrams of levers are seen on Aristotle mentions them er soph philo sculptures. The ancient Greek levers to build huge used y osedl supp s mede Archi gs. writin in his out of the water ships n Roma ing invad cranes that were able to lift rocks. He also built on ships the hing smas ur, harbo use of Syrac ing ships from under other machines that sat on the bottom, grabb ers fell off. It is possible water and shaking them until all the soldi a, however. What is gand propa nt that this was all just ancie and said, ‘With a lever levers ed studi he that is n know itely defin move the world’. long enough and a point to stand on, I could

effort

load

Force multipliers: class 1 and class 2 levers Class 1 levers (or first order levers) have the load at one end, the effort force at the other and the fulcrum somewhere in between (Figures 9.2.1 and 9.2.2).

fulcrum load

Prac 1 p. 274

effort

effort

fulcrum

Fig 9.2.2

Some class 1 levers

load

fulcrum A class 1 lever

Fig 9.2.1

Class 2 levers (or second order levers) are also force multipliers and have the fulcrum at one end, the effort at the other and the load somewhere in between. They can move heavy loads by putting in a little effort a long way from the pivot (Figures 9.2.3 and 9.2.4). Where you apply the effort in these levers is just as important as the effort itself. The effort required

269

>>>

Levers depends on the distance of the load from the fulcrum and where on the lever we put our effort. As with the ramp these levers reduce the effort by increasing the distance the load must be moved.

Class 1 and 2 levers obey a rule called the Principle of Levers: of load from fulcrum

effort x distance = load x distance A class 2 lever

Fig 9.2.3

of effort from fulcrum

This means that a 60 kg student would need to sit 2 metres from the pivot of a seesaw to balance their 40 kg younger sister who is sitting at the very end, 3 metres from the pivot. Proof: 60 x 2 = 40 x 3.

load

Prac 2 p. 275

Mechanical advantage in levers fulcrum effort

You will that mechanical advantage gives us an idea about how effective a machine or technology is. For levers, mechanical advantage can be calculated in two ways: mechanical advantage = load/effort =

distance of effort from fulcrum distance of load from fulcrum

For levers, the best mechanical advantage is achieved when the effort is far from the fulcrum and the load is close to it (Figures 9.2.5 and 9.2.6).

ad

lo

fulcrum

The higher the mechanical advantage, the better the machine.

Fig 9.2.5

lo

ad

load effort

effort

effort

low mechanical advantage

high mechanical advantage

load

load

load

effort

Speed multipliers: class 3 levers fulcrum

Fig 9.2.4

270

Some class 2 levers

Class 3 levers (or third order levers) are not used to decrease the required effort. Instead they get the load (often a small one) moving at an increased speed.

oad

fulcrum

UNIT

9 .2 fulcrum

load

load

effort

effort

load fulcrum effort

A class 3 lever

Fig 9.2.6

These levers have the fulcrum at one end, the load at the other end and the effort (usually from our hands) somewhere in between. Bats and racquets are all class 3 levers. We move our hands a short distance at high speed so the ball travels from the bat at an even higher speed: class 3 levers are speed multipliers. Because the distance the ball moves is large, the force on it is small. This requires your hand to move a small distance but with a large effort. Worksheet 9.2 Levers in our body

UNIT

9. 2

Prac 3 p. 276

Prac 4 p. 276

[ Questions ]

Checkpoint Force multipliers: class 1 and class 2 levers 1 What is a force multiplier? Explain using an example. 2 Define the term ‘fulcrum’ and identify alternative names for it. 3 Construct a sketch of a playground seesaw. Draw where you would place a heavy person to balance a light person sitting on the very end of one side. On your diagram, mark the fulcrum, effort and load.

load

fulcrum

Fig 9.2.7

effort

Some class 3 levers

Speed multipliers: class 3 levers 6 Explain how a class 3 lever acts as a ‘speed multiplier’. 7 State the advantage of using a class 3 lever in most ball-sports. 8 A sword is an example of a class 3 lever. Explain why.

Think 9 Describe three examples of a lever in action. 10 Copy the following into your workbook, modifying any incorrect statements so they are true. a All levers are force multipliers. b The fulcrum of a lever is always somewhere in the middle. c A golf club is an example of a force multiplier. d A pivot is the same as a fulcrum. e A speed multiplier is needed in most ball-sports. 11 Define the Principle of Levers.

4 Explain how mechanical advantage is calculated for levers.

12 A heavy rock is to be shifted, and all you have is a long metal bar and another smaller rock. Illustrate how you would shift the rock. Label the load, fulcrum and effort.

5 Describe how a greater mechanical advantage may be obtained when using a lever.

13 Which class of levers is the most effective in lifting a load? Justify your answer.

Mechanical advantage in levers

271

>>>

Levers

Analyse 14 Classify the objects in Figure 9.2.8 as class 1, 2 or 3 levers.

a

c

b

d

Fig 9.2.8 15 Calculate the mechanical advantage of the levers shown below.

a

mass #1

10 N load

5 N effort fulcrum 10 cm

16 A seesaw ruler was set up as shown below. Different masses were added to each side so that the seesaw was just balanced. Copy and complete the results table.

mass #2

pivot

5 cm

distance mass #1

15 N load

b

5 N effort

Fig 9.2.10

fulcrum 3m

6m

c 25 N effort 5 N load

fulcrum

Mass #1 (g)

Distance of mass #1 from pivot (cm)

Mass #2 (g)

6

4

8

6

4

1

20 cm

80 cm

1

3

6

Distance of mass #2 from pivot (cm)

12 12

10

8

Fig 9.2.9

272

distance mass #2

2

5 9 16

UNIT

9 .2 [ Extension ] Surf

Investigate 1 Collect photos of levers from magazines, advertising brochures and newspapers. a Classify each lever as class 1, 2 or 3. b Identify and label the effort, fulcrum and load on each lever. 2 Construct a poster to demonstrate how different levers are used in sport.

Investigate the following information about levers by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button. 4 Revise how levers work by completing an interactive levers activity. 5 Archimedes used simple technologies to invent many different machines. Investigate Archimedes and his work, then write a short biography of his life.

3 Muscles can only contract (get shorter and thicker) or relax (get longer and thinner), pulling the bone up or letting it down. Muscles provide the effort force that controls bone levers. Use a diagram of the muscles of the body to identify the names of the muscles used to flex your arm and to straighten it.

Project Making body parts 1

Make a larger version of the ‘skull’ shown in Figure 9.2.11 out of cardboard. Use a paperclip to hinge the jaw to the skull and a deflated balloon for the muscle that controls it. Explain what happens to the ‘muscle’ as the jaw opens and closes.

2

Use the diagram in Figure 9.2.12 to construct a model of the human arm, its bones and muscles. Describe what happens to your ‘balloon muscles’ as you straighten and flex your model arm. How does this compare with your real arm muscles? An arm lever

Fig 9.2.12

skull first wooden strip

second wooden strip

hinge

balloon lower jaw upper arm

Fig 9.2.11

balloon (muscle) string

Construct a jaw-lever

lower arm balloon (muscle)

273

>>>

Levers

UNIT

9.2

[ Practical activities ] The seesaw Aim To investigate the seesaw as a lever

Prac 1 Unit 9.2

Equipment 7 small masses (such as 5 cent coins), ruler, a fulcrum or pivot (a pencil is ideal), an elastic band

Method 1 Set up a seesaw as shown in Figure 9.2.13.

4 Place four of the small masses on the left side of the ruler and another four on the right and arrange them until the seesaw is balanced. 5 In the table, record the distance of each pile of masses from the pencil fulcrum. Repeat with two masses on the left and three on the right. 6 Repeat for all the other masses shown.

Questions

ruler

pencil

1 What do you notice about your answers in columns 3 and 6? Interpret what you notice. coins

elastic band holds ruler onto pencil

A class 1 lever in action

Fig 9.2.13

2 You have just discovered the Principle of Levers. Use it to predict where you would place a 2 g mass to balance: a another 2 g mass placed 4 cm from the pivot b a 10 g mass, 2 cm from the pivot c a 6 g mass, 6 cm from the pivot d a 1 g mass, 2 cm from the pivot 3 Identify the class of lever used in this activity.

2 Use the elastic band to hold the ruler in place on the pencil. 3 Copy the results table below into your workbook.

Left-hand side Number of masses

274

Distance from pivot

Right-hand side Number of masses x distance from pivot

Number of masses

4

4

3

2

4

3

5

2

6

1

Distance from pivot

Number of masses x distance from pivot

UNIT

9 .2 Lifting books Prac 2 Unit 9.2

Aim To investigate the relationship between fulcrum position and effort on a class 1 lever

6 Now try lifting the book using the class 2 and 3 levers shown in Figure 9.2.15.

Equipment Metre ruler, rubber stopper, textbook

2nd class

Method 1 Set up the lever shown in Figure 9.2.14.

effort load rubber stopper

3rd class

fulcrum effort load

fulcrum effort load

Lifting using class 2 and class 3 levers

Fig 9.2.15

fulcrum

Questions Fig 9.2.14

Lifting a book using a class 1 lever

2 Lift the book by pushing down on the ruler with your finger. 3 Now place the stopper close to the book and repeat the experiment. 4 Repeat once more but with the stopper placed at the far end away from the book. 5 Copy the table below. Complete it using the words ‘high’, ‘medium’ or ‘low’.

Position of stopper

1 Copy the three diagrams (class 1, 2 and 3) into your workbook. Add arrows to show the effort and load forces. Label the fulcrum. 2 The force needed to lift the book using the class 1 lever changed as the stopper moved away from the book and towards your finger. Analyse what happened. 3 Use the Principle of Levers to explain why, in a class 1 lever, it is easier to lift the book if the fulcrum is close to it and far away from your finger. 4 Assess which class of lever made it most difficult to lift the book.

Effort required to lift the book

Far away from book Midway Close to book

275

>>>

Levers

Class 3 Levers 2 Use the spring balance to measure the effort force needed to raise the load slowly.

Aim To investigate a class 3 lever Prac 3 Unit 9.2

Equipment 1 m ruler, 1 kg mass, spring balance, brick or block to act as the fulcrum

Method 1 Copy the following table into your workbook and then set up the class 3 lever shown in Figure 9.2.16.

Spring balance reading (N)

4 Calculate the mechanical advantage for each measurement.

Load (kg)

Distance of load from fulcrum (cm)

1

100

30

1

100

40

1

100

50

1

100

60

1

100

70

A class 3 lever at work

Spring balance reading (kg)

3 Record your measurements in the table. You might need to convert the newton readings of your spring balance into kilograms by dividing your measurements by 10.

Fig 9.2.16

Distance of spring balance from fulcrum (cm)


Questions 1 Identify which was bigger—the load or the effort required to lift it. 2 Identify which was the most effective lever. Justify your answer.

Levers at work fulcrum

spring scale 100 cm

0 cm

Prac 4 Unit 9.2

Aim To examine various common implements to determine which class of lever is being used Equipment Stapler, nail clippers, scissors, pruning shears, nutcracker or bulldog clips

50 cm

load (1 kg mass)

Method 1 Accurately draw each machine. 2 Label the fulcrum, load and where the effort needs to be applied. 3 Identify the purpose of other parts of each machine.

Questions 1 Classify each lever as class 1, 2 or 3. 2 State whether each one is a force or speed multiplier.

276

UNIT

context

9.3 Most machines do not use the simple up-and-down movement that ramps and levers produce. They use a spinning or rotary motion instead. Wheels, axles and gears apply the principle of levers to our everyday lives. Although they might not look like it, a tap and a doorknob are really wheels. Gears are used in many applications from bicycles to corkscrews. Can you imagine life without the wheel?

The wheel A wheel has a fulcrum, located at the centre, called the axle. The rim, the outside of the wheel, is the other end of the lever. The rim of a rotating wheel moves a larger distance and at a higher speed than the axle, which simply turns on the spot.

movement of wheel movement of axle Fig 9.3.2

A steering wheel, a screwdriver and the key to open a can are all examples of wheels and axles.

The wheel as a force multiplier

wheel

axle centre

As with an inclined plane and levers, you gain in force what you lose in distance moved.

Fig 9.3.1

As with a lever, a wheel can be used to reduce the force needed to carry out a task. The spindle (axle) of a doorknob or tap is nearly impossible to turn with bare fingers. A doorknob or a tap can be either a simple lever or a ‘wheel’. A small force moving the end of the handle or the edge of the knob or tap will turn the spindle easily enough to unlock the

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Levers door or turn on the tap. A small effort applied to the rim has produced a large turning force at its axle: the force has been multiplied. In science, the turning effect of a force on an object is called torque. Torque is calculated by multiplying the applied force by its perpendicular distance from the turning point. Torque is measured in newton metres (Nm). Car magazines frequently report on the torque Prac 1 p. 281 developed by cars.

Fig 9.3.3

A ceiling fan is an example of a speed multiplier.

Fig 9.3.5

high speed

low speed

A tap may use a lever or a wheel.

Changing the motion

Fig 9.3.4

A doorknob may use a lever or a wheel, too.

Once a spinning motion has started, its direction, speed or location often needs to be changed. The simplest way to do this is to connect wheels of different diameters together with belts. A smaller-diameter wheel will spin faster and with greater Prac 2 p. 282 force if it is connected by a belt to a larger wheel.

The wheel as a speed multiplier Wheels can also be used as speed multipliers. A slowly spinning axle turns the rim at a higher speed. The blades of a fan or a propeller must spin very fast to move the quantities of air needed to cool or to move an aircraft along. The motor turns the axle relatively slowly. The bigger the propeller, the faster the blade tips will go and the more air is moved.

278

A fanbelt connects wheels of different sizes.

Fig 9.3.6

Gears

Gear trains

Gears can also be used to change speed, torque or the direction of rotation. A gear is a wheel with identical teeth around its edge. If the axle turns it, it is call the driving gear. If the teeth of another gear (called the driven gear) mesh with the driving gear it too will turn, but in the opposite direction. The speed and torque of the driven gear depends on its size compared to the driving gear. This relationship is shown in Figure 9.3.7. Gearing up, gearing down and parallel gearing

Fig 9.3.7

driven gear

driven gear fast

driving gear

driving gear

slow

slow fast gearing up

gearing down

parallel gears

A gear train is a series of two or more connected gears. If the gears are identical, they Ancient gears both turn at the same speed The first-ever calculator but in different directions. seems to be a machine built by the ancient These are called parallel Greeks in the first gears. century BC. It was built If the driven gear is to predict the timing of eclipses and contained smaller than the driving gear, thirty-two bronze gears. it will rotate faster: the gears When it was discovered act as a speed multiplier. This in 1901 in the wreckage of an ancient ship sunk is called gearing up and is in the Aegean Sea, it useful when high-speed looked like a lump of rotation is needed, say, in a metal covered in barnacles. The gears power drill, kitchen blender, and its function didn’t or coarse focus knob on a become obvious until it microscope. was X-rayed in 1972. Gearing down is when a small driving gear rotates a larger one, which turns at a slower speed. The torque applied is multiplied, making it useful in situations where a strong turning force is required. Gears on bikes use this to make the hard job of climbing hills easier and to allow swift acceleration from traffic lights. Types of gears you will commonly find are rack and pinion, idler, worm and bevel gears. These are shown in Figure 9.3.9; they do different jobs but all work in much the same way. Worksheet 9.3 Gears

Fig 9.3.8

Prac 3 p. 283

UNIT

9.3

Prac 4 p. 283

An eggbeater changes both the speed and direction of rotation.

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Going for a spin: wheels, axles and gears Spur, rack and pinion, worm and bevel gears

Fig 9.3.9

Think spur gear

worm gear

rack and pinion gears bevel gears

14 Copy the following into your workbook, modifying any incorrect statements so they are true. a Rotary motion is up/down motion. b The axle and the rim of a wheel are the same thing. c The driving wheel of a bicycle is an example of a speed multiplier. d Parallel gears turn in the same direction. e The steering wheel of a car is an example of a speed multiplier. f Gearing up is used when high-speed rotation is needed. g Gearing down is used in drills and kitchen blenders. 15 Construct a diagram of a bicycle wheel. Label its axle and rim. Show where the wheel would move the fastest/slowest and where the torque that could be applied would be the greatest/smallest.

UNIT

9. 3

[ Questions ]

Checkpoint The wheel 1 Describe how a wheel is like a lever.

16 a Draw two gears that would act as a speed multiplier and another two acting as a force multiplier. b Identify and label the driving and driven gears in your diagram.

Analyse 17 Predict the direction of rotation and the speed of the gears in Figure 9.3.10.

2 State another name for the fulcrum of a wheel. 3 Define torque. 4 Identify another name for the axle of a doorknob or tap. 5 Draw a labelled diagram to demonstrate how a wheel can act as a speed multiplier.

slow

a

6 List examples of wheels being used as speed multipliers. 7 Explain how the direction of a spinning wheel can be changed.

Gears

b

fast

8 Copy and complete: Gears can be used to change ________, ________ (________ force) or the direction of ________. 9 Distinguish between a driving gear and a driven gear. 10 Explain when gearing up and gearing down are used. 11 Copy and complete: The speed of a driven gear and the torque it can apply depend on ________.

slow c

12 Define a ‘gear train’. 13 Draw or trace diagrams of rack and pinion, idler, worm and bevel gears.

280

Fig 9.3.10


UNIT

9.3 Create 2 Use the diagram in Figure 9.3.11 to construct a mouse-trap racer.

1 Examine a bicycle closely. a What are the gears in a bicycle called? b Draw a diagram to illustrate your answers to the following questions. i How many gears are there front and back in a 10-speed bicycle? ii How many teeth does each gear have on it? iii Do they mesh together? How are they connected?

string

mousetrap

c Construct diagrams to show the arrangements of front and rear gears that a cyclist would use to: i travel at high speed ii climb a steep hill iii ride downhill d Gear ratio is the number of teeth on the front gear divided by the number of teeth of the back gear. i Count the number of teeth on each gear used in part c and calculate the gear ratio for each situation. ii Describe what sort of gear ratios are needed for each situation.

UNIT

9. 3

axle

Fig 9.3.11

Surf 3 Explore further how gears work by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button.

[ Practical activities ] A simple wheel and axle

Prac 1 Unit 9.3

paperclips

Aim To construct a simple wheel and axle Equipment

tape

250 mL beaker or tin can, 100 g mass, 2 paperclips, flexible drinking straw or satay stick, cotton thread, sticky tape

straw or satay stick

Method 1 Set up the apparatus as shown in Figure 9.3.12. 2 Try to lift the 100 g mass by turning the straw or satay stick. 3 Bend the straw or satay stick without breaking it, and try again.

Questions 1 State whether you were able to lift the 100 g mass without bending the straw or stick.

100 g mass

A simple wheel

Fig 9.3.12

2 Propose a way of making the job even easier.

>> 281

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Going for a spin: wheels, axles and gears

Roping them together Aim To investigate speed changes by connecting Prac 2 Unit 9.3

different-sized wheels

5 Draw an obvious line on each of the lids with the marker.

Equipment

6 Measure the diameter of each lid.

A variety of circular lids of different sizes from jam jars etc (serrated edges are ideal), elastic bands, a piece of wood, a small sheet of thin cardboard, pins, small nails or tacks (they must have a circular cross-section), marking pen, hammer

Method

8 Record your results in a table like this:

1 Put small holes in the exact centre of two lids. 2 Cut several elastic bands and tie them together so that they go right around two lids.

7 Start one wheel spinning. Note which direction the wheels turn and use the line you have drawn to count how many times each lid turns in one minute. You have just measured the rpm (revolutions per minute) of each wheel.

Diameter wheel #1

Clockwise/ anticlockwise?

3 Cut out small circular ‘washers’ from the thin cardboard. 4 Assemble your wheels as shown in Figure 9.3.13. The elastic band should be stretched just a little. Roping wheels together

Fig 9.3.13

rpm wheel #1

Diameter wheel #2

Clockwise/ anticlockwise?

rpm wheel #2

9 How does the size of the wheel affect the force needed to do a job? 10 Try different combinations of lids. 11 Change the elastic band to look like a figure 8, and repeat the experiment.

Questions step 1

1 How did the rpm of a small wheel compare with the rpm of the larger wheel it was connected to? 2 Analyse whether there is a link between wheel diameter and rpm. 3 State whether the wheels spun in the same or different directions.

step 2

figure 8

282

4 Recount what happened when the elastic band was changed to a figure 8.

Model building

Geared machines Prac 3 Unit 9.3

Aim To investigate common implements that use gears Equipment Eggbeater, hand-drill, corkscrew, adjustable spanner

Fig 9.3.14

UNIT

9.3 Aim To build various models using gears, levers Prac 4 Unit 9.3

and wheels

Equipment Model building set such as Lego

Method 1 Use two gears to make a gear train that gears up, and another that gears down. 2 Connect an arrangement to turn the driving gear of each and something that will be spun by the driven gear. 3 Draw your machines. 4 Rotate the driving gear slowly, adding to your diagram the direction the gears move in. 5 Count how many teeth each gear has and the number of times the driving gear must be turned to rotate the driven gear ten times. 6 Put all numbers and ratios on your diagram.

Method 1 Carefully draw the gear arrangements in the machine you have been given, labelling each type of gear (rack and pinion, worm, etc.). 2 Label which gear is driving and which is driven, and the direction each gear moves in.

7 Construct a machine like the one in the previous experiment.

Question 1 Use the numbers of teeth to calculate the gear ratio, and the number of turns to calculate the turn ratio of each.

3 Label any levers or wedges that might also be there. 4 Count how many teeth are on each gear. Put these numbers on your diagram.

Fig 9.3.15

Can you build models of the following geared machines?

5 Make a small mark on the side of the driving gear and another on the driven gear. 6 Turn the driving gear slowly and count the number of times each gear turns. Stop when one of the gears has turned ten times. Write the number of turns on the gears on your diagram.

Questions 1 Identify which gear was the largest—the driving or the driven gear. 2 Explain what the job of your machine is. 3 Does your machine need to be a force multiplier or a speed multiplier? Justify your answer. 4 Calculate the gear ratio by dividing the number of teeth of the biggest gear by the number of teeth of the smallest. 5 Calculate the turning ratio by dividing the biggest number of turns (you chose ten) by the smallest number of turns. 6 What do you notice about the two ratios?

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UNIT

context

9. 4 Humans usually find pulling an object down a lot easier than lifting it up. Our weight already acts downwards and so we can use it to help us pull down. A pulley can be used to convert a lifting force into a pulling-down force. A pulley is simply a wheel with a grooved edge where a string, rope or chain can run.

upper pulley wheel lower pulley wheel

effort

Introducing pulleys A single pulley makes the job of lifting an object easier but only because it changes the direction of the effort force. You still need to put in the same effort that you would if you were lifting the object: the mechanical advantage should be equal to one. In fact you probably need to put in more effort, since you need to overcome the load and some friction in the pulley. Friction always makes us work harder, by reducing the effectiveness or efficiency of machines. Bigger loads can be lifted with little effort if a system of two or more pulleys is strung together.

pulley

Fig 9.4.2

A double pulley system halves the effort required. Double the load can be lifted, but the distance we need to pull the rope is also doubled.

The pulleys now become a force multiplier: we put in an effort and the pulley multiplies it, so we can lift heavier loads. A multiple pulley system, such as that shown in Figure 9.4.2, is often called a block and tackle or sometimes a Prac 1 p. 286 chain hoist.

How do pulleys reduce effort? effort

load A single pulley makes the job easier by changing the direction of the effort.

284

load

Fig 9.4.1

Imagine we need to lift a refrigerator two metres onto a truck. With a single pulley we need to pull the rope down the same distance, two metres. If we use a double pulley, however, the distance that the rope needs to be pulled is doubled, making it four metres.

Whoops! Thomas Midgley (born 1889) discovered in 1921 that tetra ethyl lead could be added to petrol to stop ‘knocking’ in car engines. In 1928 he realised that chlorofluorocarbons, or CFCs, would be perfect as a refrigerant. They couldn’t catch fire, were nontoxic and odourless if they leaked, and they wouldn’t rust the fridge. When stricken by polio in 1940, he became partially paralysed and he invented a system of pulleys and ropes that could lift him from bed to wheelchair. Unfortunately, all his discoveries and inventions proved to be harmful: lead from car exhausts slowly polluted the air in busy cities, poisoning their inhabitants; CFCs caused depletion of the ozone layer; and Thomas himself was strangled to death when he became tangled in his own pulley and rope contraption in 1944.

The advantage is that we need to use only half the effort. You will from the section on ramps that work is the energy needed to move something: work = effort force x distance moved

Archimedes again! Archimedes also used pulleys to make machines. Using levers and a primitive pulley system, he enabled his king to drag a fully loaded warship out of the water.

If the distance we move is greater, the effort we need to put in is less. This is how multiple pulleys work: we need to pull further but we put in less effort.

UNIT

9. 4

The effort needed gets less if more pulleys are added to the system: the mechanical advantage equals the number of pulleys used. Unfortunately, friction once again makes us work harder, by reducing the efficiency of a pulley Prac 2 Prac 3 Prac 4 system. p. 287 p. 287 p. 287

UNIT

9.4

Worksheet 9.4 Pulleys

[ Questions ]

Checkpoint Introducing pulleys 1 Explain why humans naturally find pulling an object down easier than lifting it up. 2 State the main advantage of using a single pulley to lift a load.

13 Identify how many pulleys are in each arrangement in Figure 9.4.3. 14 Determine what force multiplication each pulley arrangement in Question 13 would give.

3 Describe the mechanical advantage of a single pulley. 4 Define a ‘block and tackle’.

How do pulleys reduce effort?

a

b

5 Using the work formula, describe how a pulley reduces effort. 6 If we use two pulleys instead of one, describe what happens to the effort and distance we must pull.

Think 7 Distinguish between a pulley and a gear. 8 Friction is a nuisance in a pulley. Explain. 9 Identify the advantage of using a clamp together with a pulley. 10 A hoist does not use rope over a pulley. Identify what it does use. 11 Are pulleys force or speed multipliers? Explain.

Analyse 12 Outline the advantages and disadvantages of using multiple pulleys.

Fig 9.4.3

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Pulleys

[ Extension ] Create 1 Research the pulley arrangements used in car repair shops, yachts and simple cranes. Construct models of each pulley arrangement using weights to mimic the real thing. 2 Construct a model to demonstrate how ramps, wedges, wheels, pulleys (and any other machines) were used in constructing the pyramids.

Action 3 Use Figure 9.4.4 to design a tug-of-war competition that you cannot lose. Add more opponents until you find the maximum number of people you can defeat.

UNIT

9. 4

Fig 9.4.4

[ Practical activities ] Fixed and moveable pulleys Pulley arrangements to try

Aim To investigate the Prac 1 Unit 9.4

mechanical advantage of various pulley configurations

Fig 9.4.5

retort stand

Equipment

a no pulley

100 g mass, spring balance, retort stand, strong cotton thread

spring balance

b fixed pulley

100 g

Method

100 g

1 Use a spring balance to measure the effort force needed to hold a 100 g mass in each of the situations shown in Figure 9.4.5. 2 Record your readings in a table similar to the one shown below.

c moveable pulley

3 Now use the fixed pulley (b) and moveable pulley (c) in Figure 9.4.5 to gently lift the 100 g mass. What are the spring balance readings now?

100 g

‘Pulley’

Questions 1 Did the fixed or moveable pulley require less effort to hold and lift a mass? Propose a reason why.

286

a

No pulley

b

Fixed pulley

c

Moveable pulley

Effort need to hold the mass (N)

Effort needed to lift the mass (N)


UNIT

9.4 Paperclip pulleys Prac 2 Unit 9.4

Aim To compare single and double pulleys made from paperclips

retort stand d double pulley

Equipment 100 g mass, spring balance, retort stand, strong cotton thread, paperclips

paperclip

Method

thread

1 Use a spring balance to measure the effort needed to hold a 100 g mass as shown in Figure 9.4.5 part a. Record its reading.

paperclip

2 Twist the two paperclips apart as shown in Figure 9.4.6 and construct the double-paperclip pulley as shown.

100 g

3 Now use the paperclip pulley to gently lift the 100 g mass. Record the new spring balance reading. 4 Measure the effort required to hold the 100 g and then the effort required to gently lift it.

Questions 1 Did the double pulley make the jobs of holding and lifting easier or harder?

Fig 9.4.6

A double pulley system

2 These paperclip pulleys are not as good as pulleys with moving wheels. Assess why. 3 Calculate the mechanical advantage of the single and double paperclip pulleys.

Using pulleys Prac 3 Unit 9.4

Aim To construct pulley systems to lift various masses Equipment

4 Place the 500 g mass (the load) on the desk next to the books and lift it slowly to the top with the spring balance.

2 single pulleys, 2 double pulleys, 1 m string, a set of 50 g masses, spring balance, ruler

5 Read the effort force required and record it in your table.

Method 1 Construct a table or spreadsheet as shown below. 2 Use the spring balance to measure the effort needed to hold a 500 g mass. This is its weight force. 3 Pile some textbooks on your desk to about 5 cm to 10 cm high, then measure the exact height.

Arrangement

Mass used (g)

a

No pulley

500

b

Spring balance upside down

500

c

One pulley

500

d

Two single pulleys

500

e

Two double pulleys

500

Weight force (N)

6 Also measure the distance your hand had to move to lift the load to the top of the books. 7 Repeat, but with the spring balance upside down. 8 a string over a single pulley and use it to lift the 500 g to the top of the books. Once again measure the effort required and the distance your hand had to move.

>> Effort force required (N)

Distance mass Distance hand lifted (cm) moved (cm)


287

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Pulleys

a

9 Repeat with the other combinations shown in Figure 9.4.7 or some of your own designs.

b spring balance

upside down

10 Calculate the mechanical advantage for each arrangement.

Questions

books 500 g

5–10 cm

c

500 g

d

5–10 cm

1 Was there any difference in the reading of the spring balance when it was upside down? If so, propose why.

e

2 Identify any advantage in using a single pulley. 3 Describe what happened to the effort force as more pulleys were added.

load effort

effort effort

5 Write a conclusion for your findings. load

Fig 9.4.7

4 Describe what happened to the distance your hand moved when lifting the mass.

load

Test these pulley systems.

4 Use the ‘pulley’ to lift the 100 g mass 5 cm. Measure how far you needed to move your hand to do so. 5 Repeat, but with four, then six, then eight sections of thread.

Rope sections Prac 4 Unit 9.4

Aim To construct a pulley system using common materials Equipment fixed pulley

Strong wire that can be bent (coat hangers are ideal), retort stand and clamp with ring, strong cotton thread or string, 100 g mass

Method

thread

1 Construct a table like the one shown here.

moveable pulley

100 g

Number of sections of thread

Distance mass moved (cm)

How far hand moved (cm)

2

5

4

5

Questions

6

5

8

5

1 Describe what happened to the distance your hand moved to lift the mass when the number of sections of thread increased.

Making a multiple pulley

Fig 9.4.8

2 Evaluate what this suggests about the effort required. 2 Build the ‘pulley’ arrangement as shown. 3 the cotton thread or string over the ‘pulley’ so that there are two sections of string ing the mass.

288

3 Use your knowledge of the formula work = effort x distance to explain your answer.

UNIT

context

9.5 Simple machines and the technology behind them make jobs easier. A complex machine is one made by connecting a number of simple machines so that their technologies become even more useful, allowing us to do things that were previously impossible.

Doing the impossible: flying Humans have always wished they could fly and have the freedom of movement that birds have. The great Renaissance artist and scientist Leonardo da Vinci drew some of the earliest sketches of flying machines, producing two different designs using the simple technologies of the time. One drawing was of a flying machine that used flapping wings to imitate the flight of birds. Another was an aerial screw, a drag primitive ancestor of the helicopter, and is shown on the chapter opening page. Without help we can’t fly or even travel very fast. The successful and unsuccessful flying machines of history have all used the simple technologies that we looked at in the previous units: gears and pulleys to turn the propellers (which are really a screw or inclined plane), and levers to move the flaps on the wings. King Bladud, Two other technologies were the first pilot The first recorded ‘flight’ required, however, before flight was made by Bladud, the was possible. A flying machine ninth King of Britain, in needs to be light, and so in the 843 BC. Unfortunately, King Bladud had simply early days the materials used strapped wings made were often light wood, bamboo, out of feathers onto his paper and oiled canvas. arms, so his flight was Nowadays, scientists working in very short, very vertical and had a very the technology of materials are messy landing. producing lighter and stronger

materials such as titanium, carbon fibre and special alloys for use in aircraft. Wings also need a special curved wedge shape to help give the aircraft the ‘lift’ required to take off. Although modern aircraft use a series of technologies to allow them to operate, the science behind them is quite simple. An aircraft has four important forces acting on it: weight, lift, thrust and drag, as shown in Figure 9.5.1.

lift

thrust

weight

The forces on an aircraft

Fig 9.5.1

You will that a force is a push, pull or twist that accelerates (speeds up) or decelerates (slows down) an object or changes its direction or shape. Force is measured in newtons (N). An aircraft stays in the air because of an Prac 1 upward force called lift produced by the p. 292 wings. The special shape of the wings is called the air foil or aerofoil. The top surface of the wing is longer than the bottom surface, making the air move faster over the top so that it can catch up with the air moving the shorter distance underneath the wing.

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The technology of complex machines No air? No aircraft!

High-speed air has lower pressure than air that is slow or not moving. This causes the wing to be ‘sucked’ upwards, taking the aircraft with it. Lift depends on air moving over the wings. As an aircraft picks up speed on the runway, the lift builds until it is greater than the aircraft’s weight. This is when the aircraft takes off. The forces are now unbalanced: there is an overall push upwards lifting the aircraft into the air.

Aircraft would not be able to take off on the Moon. The lack of atmosphere means no lift force is possible, so aircraft would always stay on the ground regardless of how fast they travelled. Helicopters would also be grounded. Rockets are the only craft that can take off when there is no air.

Fig 9.5.2

An air foil at work

wing

cross section

air moves faster and has less pressure

air is slower and has higher pressure

UNIT

weight

airflow direction of travel

[ Questions ]

Checkpoint Doing the impossible: flying 1 Define a ‘force’ and describe what it can do to an object. 2 Explain what is meant by balanced and unbalanced forces, giving examples of each. 3 Copy the following into your workbook, modifying any incorrect statements so they are true: a Air moving over an air foil causes thrust. b The top part of a wing is longer than the bottom.

290

Thorpedo A biomechanist is a scientist who studies the motion of the human body, particularly in sport. Biomechanists have studied champion swimmer Ian Thorpe and suggest that his 22 cm long hands act something like an air foil and provide him with ‘lift’ in the water in addition to his normal buoyancy. His size 18 feet are 35 cm long and provide exceptional thrust. His drag in the water is drastically reduced by wearing an Adidas swimsuit made of Tefloncoated lycra. Teflon is also used in non-stick fry pans. Swimsuits by Speedo are made from a fabric called ‘Fastskin’ that has a texture modelled on sharkskin.

lift

air must travel further over the top

9. 5

At cruising altitude the lift is the same as the weight: the aircraft stays at the same height because the forces are balanced. As the aeroplane approaches the airport it slows down and the lift decreases, making the forces unbalanced once more. The aeroplane’s weight is greater than the lift, and so it starts to descend. Lift needs speed, and an aircraft gets this from jet engines or propellers that push it forward; this force is called thrust. Friction caused by air sliding around the aircraft slows it down, and is called drag. Aeroplanes have streamlined shapes designed to minimise drag. Worksheet 9.5 Whirly bird

c Fast-moving air has higher pressure than slowmoving air. d An aircraft will take off only if the lift is greater than the weight. e There is no overall force on an aircraft when it is at cruising altitude. 4 Outline the four forces that are important in the flight of an aircraft.

Think 5 Identify what is special about the shape of an air foil. 6 Explain how an air foil creates lift. 7 Justify why an aircraft needs to pick up speed on a runway before it can take off. 8 Propose reasons for the following: a Aircraft always try to take off by heading into the wind. b Heavy aircraft need longer runways to take off. c There is no lift and no drag on an aircraft that is stationary. d Aircraft need longer and faster run-ups on hot days than on cold days.

Analyse 9 Construct simple diagrams to show aircraft in the following situations. Include arrows to demonstrate the forces involved. State whether the aircraft is taking off, landing, cruising, at the departure gates or in trouble. a Lift is zero, thrust is zero and drag is zero. b Lift equals weight and thrust equals drag. c Lift is greater than weight and thrust is greater than drag. d Lift is less than weight and thrust is less than drag. e Lift is less than weight, thrust is zero and drag is high.

10 A helicopter also creates lift, but with its rotor blades. Assess what shape a rotor blade would need to be for it to provide lift to the helicopter.

UNIT

9.5 11 Illustrate the likely cross-section of a helicopter rotor blade. On your diagram indicate: a where you would expect the air to be moving fastest b where the pressure would be least c the lift force produced 12 When a helicopter is stationary, the blades on both sides of the rotor give the same lift. When the helicopter is moving, however, the blades provide more lift on one half of their spin than on the other half. Use your knowledge of air movement and lift to explain why

[ Extension ] Investigate 1 Research and construct a timeline of the major developments in human flight.

Project

2 Investigate how a pilot controls the flight of an aircraft.

Making a complex machine

3 Imagine you are a pilot. Write a travel log with details of your flight control, including an incident when you encounter turbulence.

You are to design and build a machine that can lift a small quantity of sand (the load) to a height of 10 cm. Your machine must use two or more simple machines such as ramps, levers, wheels, gears or pulleys. The machine must use less effort than would be required to lift the load directly. Only simple materials such as wood, cardboard, nails, pins, straws, elastic bands, string and cotton reels can be used. Commercial equipment like Meccano or Lego cannot be used. Write a one-page report that includes: • a labelled diagram of your machine • a list of the simple machines that you used • a description of how each machine reduced the effort required to lift the sand.

4 Research more about helicopters. Find out: a why they have a small rotor on their tail b how they get their thrust to move forward c why they don’t tip over because of unequal lift from the two sides of the rotor. Present your findings to the class in group presentations. Use a form of presentation media, such as PowerPoint.

Surf 5 Explore detailed diagrams and information about forces on an aircraft by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button.

>>

291

>>>

The technology of complex machines

Project Making an air foil Use the diagrams in Figure 9.5.3 to construct and test an air foil.

Find how many paperclips it can lift. Make and test an air foil.

Fig 9.5.3

paper

card

paper

strings to adjust the angle wing shape paperclips

UNIT

9. 5

[ Practical activity ]

Creating ‘lift’

Fig 9.5.4

Creating lift Prac 1 Unit 9.5

Aim To investigate the action of moving air to create lift Equipment 1 sheet of paper, 2 ping-pong balls, fine cotton thread or fishing line, retort stand, boss heads and clamps, sticky tape, drinking straw

Method 1 Set up the two experiments shown in Figure 9.5.4.

fine line

straw

balls ping-pong

straw

2 Blow air strongly through the straw, in the directions shown. 3 Record your observations.

blow air through straw

Questions 1 In this experiment you have created movement by ing air quickly over a surface. Construct a diagram of each situation, and identify where the air is moving the fastest, where the air has the lowest pressure, and the direction of any movement.

292

2 Copy and complete this sentence: An air foil is pulled into an area of ________-speed air or ________. pressure. 3 Have you created lift in this experiment? Explain.

Science focus: Indigenous technology Prescribed focus area: The applications and uses of science A typical spear thrower on top of a pile of hunting boomerangs.

Fig SF9.2

Many ancient civilisations used simple machines to their advantage. Although indigenous Australians moved about to exploit the seasons, and rarely built substantial dwellings, they did use simple machines. Their skill in making observations and their understanding of the environment they lived in allowed them to develop many clever innovations. Most notably the early Australians used their knowledge of forces and simple machines very effectively to aid them in hunting.

The spear thrower The basic design of the spear thrower was similar in many indigenous groups, but the name for this tool varied in different areas. Known as the woomera (wommera/wamarr) in New South Wales or mirr in Western Australia, the spear thrower was a very effective device to increase the time that a force was applied to propel the spear. The spear thrower usually consisted of a piece of wood that

Fig SF9.1

was carefully shaped to be held at one end, and had a hook-like peg, sometimes made from a bone or stone, at the other end. The hook-like peg at the end of the spear thrower fits into a hole at the end of the spear. The shape of the spear thrower varies depending on where it was developed. Modifying the shape allows the spear

An Aboriginal using a spear thrower when hunting

293

Fig SF9.3

The spear thrower is a lever that acts as an extension of the arm, and is a speed multiplier.

1

2

4

thrower to also be used for other purposes, such as a water scoop, a digging stick or a simple axe. As you can see in Figure SF9.3, the spear thrower acts as an extension of the thrower’s arm. The spear thrower uses two levers to launch the spear. Both levers act as speed multipliers, producing an increase in the speed of the spear compared to the speed of the thrower’s arm and hand. The first lever has its fulcrum at the shoulder and its load at the hand, as shown in diagrams 1 to 3. This is the natural throwing lever of the arm, and would be the normal lever if a spear thrower was not used. Diagram 3 shows the second lever coming into action. This lever has a complex fulcrum involving the shoulder, the hand and the hook-like point where the spear attaches to the spear thrower. To use the spear thrower effectively, as the arm reaches the normal release point (like throwing a ball), it is then swept forward and down very quickly (a bit like the follow-through of a fast bowler in cricket). This causes the top of the spear thrower to travel rapidly forward, acting like an extension of the arm. This second motion, where the end of the spear thrower effectively increases the speed of the hand, allows the force to be applied to the spear for longer than would be the case without the spear thrower. This results in the spear being launched with considerably more

294

3

5

6

speed than could have been achieved if it had simply been thrown by hand. An added bonus of the spear thrower is that the force on the spear is applied directly along the shaft, allowing a skilled thrower to be extremely accurate.

The boomerang—throwing sticks The returning boomerang that we commonly think of as being for recreation rather than hunting originated from specially shaped sticks used

Fig SF9.4

Hunting boomerangs with different shapes

A

different flight paths they follow when thrown. One surface is usually flat, while the other is curved into the shape of an air foil (just like a wing). This is why there are right-handed and left-handed boomerangs, and why boomerangs can ‘hover’ for some time in the air. The flight of a returning boomerang involves some complex physics created by the combination of lift created by the wing-like surfaces moving through the air, and the ‘gyroscopic’ forces created by the rapidly rotating boomerang (just like a spinning top).

C

B

Different returning boomerangs: A Novice/‘rotor’, B Intermediate/‘crow’, C Advanced/‘lobed’

for hunting. Several forms of boomerang-like throwing sticks were used by different indigenous tribes. These throwing sticks were carefully shaped according to the purpose they were going to serve and the prey they were to be used to hunt. It is the different curvature of the surfaces, and the shape of the boomerang, that give rise to the

Fig SF9.7

The boomerang acts as a wing with two leading edges. The forces shown here are those acting just after the boomerang is launched.

Fig SF9.5

Direction of rotation

Fig SF9.6

Cross section of wing at point shown Leading edge

Direction thrown Drag

Lift

Weight

Leading edge

A typical flight path for a returning boomerang

295

The skill of making a boomerang is ed on through observation and practice.

Fig SF9.8

[ Student activities ] 1 The spear thrower relies on two levers to act as speed multipliers in order to increase the speed of the spear when it is thrown. Describe some important things that would have to be considered when deg spears to be thrown. (Hint: how simple machines work and the Law of Conservation of Energy.) 2 a Construct and test a spear and spear thrower of your own. b Compare throwing the spear with and without the spear thrower. Which is more effective? 3 a The figure opposite shows how a returning boomerang should be released when thrown. In the sketch the boomerang is being thrown straight into the page by a right-handed person. The curved surface is to the left and the top of the boomerang is pointed in the direction it will be thrown. Describe the forces on the boomerang when it is first released. b Explain what would be likely to happen if a lefthanded person threw the boomerang in the same way as described for the right-handed person.

296

4 Examine the different hunting boomerangs shown in Figure SF9.3. a Based on their surfaces and shape, discuss their features with others and produce an outline of how each might behave when thrown. b Predict what each boomerang might be used to hunt. c Research boomerang shapes and uses to see if your predictions are correct. d Find a pattern for making boomerangs and construct your own. 5 As well as the spear thrower and the boomerang, indigenous Australians used many other technologies to make life easier. These include fire, drugs, stone tools, glues, baskets, fish traps and string. a Explore information about these technologies through the internet by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button. b From your research, construct a poster that could be used to demonstrate some of the clever innovations developed by the earliest Australians.

Chapter review [ Summary questions ] 1 True or false? a Machines make less work. b Machines reduce the effort required to do a job. c Lift is the force provided by the wings of an aircraft. d Thrust is the force that slows an aircraft as it moves through the air. e The shape of the wing of an aircraft is called an air foil. f A ramp is the same as an inclined plane. g Ramps reduce effort because the distance travelled is less. h A screw is an example of a ramp. i A machine that gives a high mechanical advantage is a good one. j A pivot and a fulcrum are different things. k Ramps and levers use rotary motion. l Wheels can never act as speed multipliers. m Two connected gears always turn in opposite directions. n Gearing up is when the driven gear turns faster than the driving gear. o Single pulleys reduce the effort needed to lift something.

[ Thinking questions ] 9 Aircraft wings flex upwards on take-off. Propose a reason why. 10 Explain how ramps reduce effort. 11 Construct diagrams of class 1, 2 and 3 levers and give three examples of each. 12 Identify what idler, worm and bevel are examples of. 13 Identify what parallel gears are. 14 Discuss the advantages and disadvantages of a single pulley. 15 A double pulley can lift twice the load of a single pulley. Determine what distance the rope must be pulled in order to do so. 16 Copy and complete: The more pulleys in a system, ________.

[ Interpreting questions ] 17 Use the principle of levers to predict where a 20 g mass should be located to exactly balance each of the see-saws in the diagram.

2 Explain what a simple machine does. 3 List six simple machines. 4 Describe what a complex machine is.

a

load

5 Copy and complete: Work = effort force x ________ 6 Distinguish between the effort and the load on a machine. 7 Construct a diagram of an aircraft, showing all important forces that act on it. 8 a Define mechanical advantage. b State whether mechanical advantage should be high or low in a machine.

10 g

10 cm b

100 g load

2 cm

18 Describe how mechanical advantage is calculated for levers. 19 Calculate the mechanical advantage for the levers in Question 17.

>>

297

>>> 20 Predict the direction and speed of the wheels and gears shown in the figure.

a

22 Construct diagrams to show how gears could be connected to: a gear down b gear up c rotate in the same direction d increase the speed of rotation e decrease the speed of rotation f change the direction of rotation by 90°

fast

23 Examine the pictures of common kitchen appliances shown below. a Identify the simple machines that are used in each appliance. b Describe how each one uses simple technologies to make life easier.

slow b

Worksheet 9.6 Simple machine technology crossword

fast c

298

21 Use examples to demonstrate a wheel acting as: a a force multiplier b a speed multiplier

Worksheet 9.7 Sci-words

a pizza cutter

b whisk

c waffle iron

d tongs

e garlic crusher

f corkscrew

consumers, 189 contraception, 177–178 convection current, 123, 125 convex (lenses), 100–101 copulation, 177 covalent compounds, 47–48 critical angle, 93–94

bases, 58–59, 61 big bang, the, 70–71, 73–75 binoculars, 102 bioaccumulation, 194–196 bioenergy, 210 biogas, 211 biomass, 210–211 biotic environment, 197 black hole, 79 body waves, 135–137 boundaries (plate), 127 brain, 243 budding, 166

ears bionic, 227–228 parts of, 226–227 problems, 227 protection, 228 earthquake, 134–139 aftershock, 138 epicentre of, 134 shadow zone, 136 ecosystem, 189 electromagnetic (radiation), 256–257 electrons, 3, 17–19, 24 electronegativity of, 24 electronic configuration of, 17–18 energy levels of, 17–18 electroplating, 54 electrostatic attraction, 45 elements, 4, 29–32 artificial, 15–16 chemical properties of, 9 physical properties of, 9 embryo, 179 endocrine system, 248 endoscopes, 94–95 endothermic reactions, 40 energy, conservation of, 190 from water, 209–210 in ecosystems, 189–190 non-renewable sources of, 205 renewable sources of, 206–211 evaporation, 198 exothermic reactions, 40 extraterrestrials, 80–82 eyes animal, 219–220 defects, 220–222 parts of the, 217–218 protection, 218

carbon, 197 cycle, 199–200 Carey, S. Warren, 123 carnivores, 181 cellulose, 149, 168 central nervous system (CNS), 241–242 chemical, bonds, 41 properties, 9 reactions, 38–42 cinder cones, 150 clones, 165 colour, 110–113 absorption of, 112 addition, 111 blindness, 219 complimentary, 112 dispersion, 110 pigments of, 112 printing of, 113 primary, 111 secondary, 111 combination reactions, 51 combustion reactions, 53 composite cones, 150 compounds, 4–5 covalent, 47–48 ionic, 45–47 compression waves,135 concave (lenses), 100–101 connecting neurons, 242 conservation, 190–191

INDEX

abiotic environment, 197 acids, 57–62 and carbonates, 60 and hydroxides, 60 and metals, 58–59 and oxides, 60 and neutralisation of, 59–60 activity series of metals, 53 adrenalin, 249 aerofoil, 289–290 alkali metals, 30 alkaline earth metals, 31 allotropes, 31 amniotic fluid, 179, 181 anticline, 149 antimatter, 83 asexual reproduction, 165–166 asthenosphere, 122 atomic number, 3, 7 atoms, 3 auxins, 165–166 axon, 241

Dalton, John, 4, 14 dark energy, 74 decomposers, 200 decomposition reactions, 51 depth illusion, 93 diabetes, 252 diatomic (gases), diffusion, dilute solutions, dispersion, 104, 110 displacement reactions, 40–41 DNA, 165 dopamine, 243 doppler effect, 69 drugs (pregnancy), 181

faults, 127, normal, 148 reverse, 148 transcurrent, 149 fault scarp, 148 fertilisation, 168

299

Index fission, 143, 166 focal length, 99–100 finding the, 101 foetus, 179 folds, 149–150 anticline, 149 overfold, 149 syncline, 149 food chain, 189, 195 food pyramid, 191, 195 fossils, 156–157 fossil fuels, 152 fragmentation, 167 gametes, 167 gases, noble, 29 gears, 279–280 geological time, 157–158 geothermal energy, 207–208 gestation, 179 glucose, 251 glycogen, 251 halogens, 29–30 hearing, 226–228 herbicides, 194 herbivores, 191 homeostasis, 237 hormones, 248–253 and plants, 253 Hubble, Edwin, 70 human growth hormone (HGH), 251 hydroelectricity, 209 hydrolysis, 41 hyperopia, 221 hypothalamus, 250–251 image real, 100–101 virtual, 100–101 implantation, 178 indicators, 61–62 infertility, 184 inorganic matter, 197 insulin, 202 international space station, 87–89 interneurons, 242 in-vitro fertilisation (IVF), 184 ionic compounds, 45–48 ions, 46–48 metal, 46 non-metal, 46 polyatomic, 47 IVF, 184 lattice, 5 lava, 145 Lavoisier, Antoine, 14–15, 23, 45 laser, 222 law of conservation of energy, 190 law of conservation of mass, 191 lenses, 99–104 concave, 100–101 convex, 100–101 levers, 269–271 lift, 289 light year, 83 lithosphere, 122

300

>>> longitudinal waves, 135 love waves, 136–137 magma, 144 mantle, 122 mass number, 3 matter, conservation of, 191 menarche, 175 Mendeleev, Dmitri Ivanovich, 9 menstruation, 174 mercalli scale, 137–138 metalloids, 11, 24 metals, 11, 23 activity table of, 53 and acids, 58–59 Meyer, Lothar, 9 microgravity, 88 microscope, 102 milky way, the, 80 mirages, 94 mirrors, concave, 102–103 convex, 103–104 mixtures, 5 molecules, 5, Moseley, Henry, 11 motor neurons, 242 mountain building, 129–130 mutation, 165 myelin, 241 myopia, 221 nebula, 77 nervous system, 241–245 neurons, 241–245 neurotransmitters, 243 neutralisation reactions, 53, 59–60 neutrons, 3 Newlands, John, 9 nitrogen, cycle, 200–201 fixation, 200 noble gases, 29 non-metals, 11, 23 non-spontaneous reactions, 41 nuclear fission, 166 nucleus, 3 ocean trenches, 129 oestrogen, 175 optical fibres, 94–95 optical instruments, 101–102 ore deposits, 152 organic matter, 197 ovulation, 167 Penzias, Arno, 74 periodic table, 9–11 peripheral nervous system (PNS), 241 pH scale, 61–62 pheromones, 252 photon, 73 photosynthesis, 199 photovoltaic cell, 206 physical properties, 9 pituitary gland, 250 placenta, 179 plate boundaries, 127–130

plate tectonics, 120–122 polyatomic ions, 47 precipitation reactions, 40, 51–52 pregnancy, 180–181 and drugs, 181 and nutrition, 180 primary colours, 111 printing, 113 producers, 189 protons, 3, protostar, 77 puberty, 174–175 pulleys, 284–285 quark, 73 radioactive waste, 205 radicals, 47 rainbows, 111 ramps, 264–266 rayleigh waves, 136–137 reactants, 38 reactions, combination, 51 combustion, 53 decomposition, 51 displacement, 53 neutralisation, 53 precipitation, 40, 51–52 receptor, 237 red giant, 77 reflection, 93 critical angle, 93–94 total internal, 93–94 reflex arc, 135, 245–246 refraction, 92–93 regeneration, 166, 167 remote sensing, 256–259 reproduction asexual, 165–166 sexual, 167–168 vegetative, 167 reproductive system, female, 173–174 male, 172–173 respiration, 200 responding, 237–238 richter scale, 137–138 rift valleys, 127–128, 148 rocks (folding), 149–150 scattering, 110 screws, 266 secondary colours, 111 seismic waves, 134–135 semi-metals, 11, 24 sensory neurons, 192 SETI, 81 sexual reproduction, 167–168 sexually transmitted diseases, 183 shield cones, 150 sight, 217–222 skin, cancers, 233 conditions, 233 slide projector, 103 solar cell, 206 solar ponds, 206 solutions, insoluble, 40, 51–52

soluble, 40, 51–52 sound, 226 levels, 228 sneezing, 231 spectrometer, 70 spectrum, 69, 256–257 sperm, 167 spinal cord, 244 spontaneous reactions, 41 spores, 166 stars, life of a, 77–79 neutron star, 78 protostar, 77 pulsar, 78 red giant, 77 red supergiant, 78 white dwarf, 78 STDs, 183 stimulus, 237 subduction zones, 128–130 sun, the, 77 surface waves, 136–137 synapse, 243 syncline, 149

UNIT

9 .1

taste, 231–232 tectonic plates, 120–122 telescope, 101 testosterone, 174 thyroxin, 250 tiuch, 232–233 transcurrent faults, 149 transition metals, 32 transverse waves, 135 tropism, 252–253 tsunami, 138–139 twins, 177 ultrasound, 180 unconformity, 150 uranium, 205 vegetative reproduction, 167 vision, binocular, 219 colour, 219 Volta, Alessandro, 15 volcanic landscapes, 150–151 volcanoes, 143–145 water cycle, 198–199 water table, 199 waves, compression, 135 longitudinal, 135 transverse, 135 wedges, 265 Wegener, Alfred, 120 wheels, 277–278 white dwarf, 78 Wilson, Robert, 74 wind, 208 wind turbine generators, 208 work, 285 worm holes, 85 zygote, 167, 178

301

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