Chapter 10 Simple Machine 6m5z4

CHAPTER 10

Simple machines

CHAPTER 10

Simple machines UNIT 10.1 Analysing lever

List things around them that use the principle of the lever State what a lever can do Identify load, force and fulcrum of the lever Classify lever Explain what is meant by the moment of force Solve problems related to levers

Lever is

What is Lever ?

a) A simple machine b) Enables small effort to overcome a heavy load c) Can be used to lift heavy objects

d) Makes work easier A lever is a simple machine which turns about a fixed point called the FULCRUM (F) when a force called the EFFORT (E) is applied to overcome a resisting force known as the LOAD (L).

Types of Simple Machines

Wedge Lever

Wheel and axle

6 types of simple machines Screw Pulley

Inclined plane

What is Lever ? A lever has 3 parts a)Fulcrum (F) – the turning point or pivot b)Effort (E) – the force applied to overcome a resisting force called the load

c)Load (L) – the resisting force exerted by an object

Simple Machines E F

L

E

L

F L

E F

E L

E

E

L L L

E

F

What is Lever ? Lever can be classified into a) 1st class b)

2nd class

c)

3rd class

Classes of Levers

Lever

A lever is a simple machine which turns about a fixed point called the FULCRUM (F) when a force called the EFFORT (E) is applied to overcome a resisting force known as the LOAD (L).

3 classes of levers

First class

Second class

Third class

First Class Lever

1st class

E F

First class lever

Relative position of F, E and L

F between E and L

L

Common characteristics

• Small force is used to move a large load • Effort moves through a longer distance than the load • Effort is further from the fulcrum than the load

Common devices

• Claw hammer • Pliers • Scissors • Crowbar

Second Class Lever

2nd class

Second class lever

Relative position of F, E and L

L between F and E

Common characteristics

• Small force is used to move a large load • Effort moves through a longer distance than the load • Effort is further from the fulcrum than the load

E

F L

Common devices

• Wheelbarrow • Bottle opener • Paper cutter • Nutcracker

Third Class Lever

3rd class

E

F

Third class lever

Relative position of F, E and L

E between F and L

Common characteristics

• Large force is used to move a small load • Load moves through a longer distance than the effort • Load is further from the fulcrum than the effort

L

Common devices

• Fishing rod • Broom • Ice tongs • Human arm

1st class

E F

=

L

F

E

=

F

L

E

=

F

E

L

L

2nd class

E

F L

3rd class

E

F L

F E

L

E

F L

F

E

E

L

L L E

F

E

E

L

F

L

L

E

F

E

E

F

F

L L

What is the Moment of a Force? When we loosen a bolt using a spanner, a force that is applied has a turning effect on the spanner. This turning effect of force is known as the moment of force Spanner

Spanner P

Q

Force 18 cm

Force 7 cm

a) It is easier to loosen the bolt if you hold the spanner at position P than Q because the turning effect is greater. b) It is also easier to loosen the bolt if a larger force is applied at P to cause a greater turning effect.

What is the Moment of a Force? • The moment of a force is the turning effect of the force • The moment of a force is defined as: Moment of a force (N m)

= Force (N) x

The moment of a force can be increased by

Perpendicular distance from the pivot to the force (m)

Increasing the size of the force Applying the force at a further distance from the pivot

To Calculate the Moment of a Force

Opening a door

0.6 m

4N

Moment of a force (N m)

= Force (N) x = 4N

x

= 2.4 N m

Perpendicular distance from the pivot to the force (m)

0.6 m

Principle of Moments in a Lever The effort and the load produce opposing moments

Anticlockwise moment

When the lever is in EQUILIBRIUM, the sum of the anticlockwise moments about a point is equal to the sum of the clockwise

Principle Of Moments in a Lever When the lever system is balanced

Anticlockwise moment

Load (N) x Distance of load from fulcrum (m)

=

=

Clockwise moment

Effort (N) x Distance of effort from fulcrum (m)

Moments in a Lever

30 cm

x

250 g

400 g

Calculate the value of x using the equation below: Load (N) x Distance of load from fulcrum (m)

=

Effort (N) x Distance of effort from fulcrum (m)

Answer : 18.75 cm

CHAPTER 10

Simple machines UNIT 10.1

Appreciating the innovative efforts in the design of machine

Devices that Using the Principle of Levers

A spade Tongs

A hockey stick

Devices using the principle of levers A crane

A fishing rod A fire engine

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