21/04/2015
Density, Specific Weight and Specific Gravity
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Density, Specific Weight and Specific Gravity An introduction and definition of density, specific weight and specific gravity formulas with examples Sponsored Links
Concrete crushing machine Strong crushing ability, Low cost, High capacity &durable.Top service Density Density is defined as mass per unit volume. Mass is a property. What is weight and what is mass? the difference between weight and mass Density can be expressed as ρ = m / V = 1 / vg (1) where ρ = density (kg/m3, slugs/ft 3) m = mass (kg, slugs) V = volume (m3, ft 3) vg = specific volume (m3/kg, ft 3/slug) The SI units for density are kg/m3 the Imperial (U.S.) units are slugs/ft 3. Pounds per cubic foot lb/ft 3 is often used as a measure of density in the US, but pounds are really a measure of force, not mass. Slugs are the correct measure of mass. You can multiply slugs by 32.2 for a rough value in pounds (lbm ). 1 slug = 32.174 lbm = 14.594 kg 1 kg = 2.2046 lbm = 6.8521x102 slugs Unit converter mass Unit converter density On atomic level particles are packed tighter inside a substance with higher density. Density is a physical property constant at a given temperature and pressure and may helpful for identification of substances. densities and properties for some common materials density of water at different temperatures SI and Imperial units Example Density of a Golf ball A golf ball has a diameter of 42 mm and a mass of 45 g. The volume of the golf ball can be calculated as V = (4 / 3) π ((42 mm) (0.001 m/mm) / 2)3 = 3.8 105 m3 The density of the golf ball can then be calculated as ρ = (45 g) (0.001 kg/g) / (3.8 105 m3) = 1184 kg/m3 Example Density to Identify a Material An unknown liquid substance has a mass of 18.5 g and occupies a volume of 23.4 ml (milliliter). The density of the substance can be calculated as ρ = [(18.5 g) / (1000 g/kg)] / [(23.4 ml) / (1000 ml/l) (1000 l/m3)] = (18.5 103 kg) / (23.4 106 m3) = 790 (kg/m3) If we look up densities of some common liquids, we find that ethyl alcohol or ethanol has a density of 789 kg/m3. The liquid may be ethyl alcohol! Example Density to Calculate Volume Mass The density of titanium is 4507 kg/m3. The mass of 0.17 m3 volume titanium can be calculated as m = (0.17 m3) (4507 kg/m3) = 766.2 (kg)
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Density, Specific Weight and Specific Gravity
Specific Weight Specific Weight is defined as weight per unit volume. Weight is a force. What is weight and what is mass? the difference between weight and mass Specific Weight can be expressed as γ = ρ g (2) where γ = specific weight (N/m3, lb/ft 3) ρ = density (kg/m3, slugs/ft 3) g = acceleration of gravity (9.807 m/s2, 32.174 ft/s2) The SI units for specific weight are N/m3. The imperial units are lb/ft 3. Local acceleration g is (under normal conditions) 9.807 m/s2 in SI units and 32.174 ft/s2 in imperial units. Example Specific Weight Water The density of water is 1000 kg/m3 at 4 oC (39 oF). The specific weight in SI units is γ = (1000 kg/m3) (9.81 m/s2) = 9810 (N/m3) = 9.81 (kN/m3) The density of water is 1.940 slugs/ft 3 at 39 oF (4 oC). The specific weight in Imperial units is γ = (1.940 slugs/ft 3) (32.174 ft/s2) = 62.4 (lb/ft 3) Specific Weight for Some common Materials Specific Weight γ
Product
Imperial Units (lb/ft3)
SI Units (kN/m 3)
Aluminum
172
27
Brass
540
84.5
Copper
570
89
Ethyl Alcohol
49.3
7.74
Gasoline
42.5
6.67
Glycerin
78.6
12.4
Mercury
847
133.7
SAE 20 Oil
57
8.95
Seawater
64
10.1
Stainless Steel
499 512
78 80
Water
62.4
9.81
Wrought Iron
474 499
74 78
Material Properties
Specific Gravity (Relative Density) Specific Gravity SG is a dimensionless unit defined as the ratio of the density of a substance to the density of water at a specified temperature, and can be expressed as SG = ρsubstance / ρH2O (3) where SG = Specific Gravity of the substance ρsubstance = density of the fluid or substance (kg/m3) ρH2O = density of water normally at temperature 4 oC (kg/m3) It is common to use the density of water at 4 oC (39oF) as a reference since water at this point has its highest density of 1000 kg/m3 or 62.4 lb/ft 3. Specific Gravity SG is dimensionless and has the same value in the SI system and the imperial English system (BG). Water is normally also used as reference when calculating the specific gravity for solids. Thermal Properties of Water Density, Freezing temperature, Boiling temperature, Latent heat of melting, Latent heat of evaporation, Critical temperature ... Specific Gravities for some common Materials
Substance
Specific Gravity SG
Acetylene
0.0017
Air, dry
0.0013
Alcohol
0.82
Aluminum
2.72
Brass
8.48
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Density, Specific Weight and Specific Gravity Cium
8.57
Chromium
7.03
Copper
8.79
Carbon dioxide
0.00198
Carbon monoxide
0.00126
Cast iron
7.20
Hydrogen
0.00009
Lead
11.35
Mercury
13.59
Nickel
8.73
Nitrogen
0.00125
Nylon
1.12
Oxygen
0.00143
Paraffin
0.80
Petrol
0.72
PVC
1.36
Rubber
0.96
Steel
7.82
Tin
7.28
Zinc
7.12
Water (4oC)
1.00
Water, sea
1.02
Example Specific Gravity of Iron The density of iron is 7850 kg/m3. The specific gravity of iron related to water with density 1000 kg/m3 is SG = (7850 kg/m3) / (1000 kg/m3) = 7.85 Specific Gravities of Gases The Specific Gravity of a gas is normally calculated with reference to air and defined as the ratio of the density of the gas to the density of the air at a specified temperature and pressure. The Specific Gravity can be calculated as SG = ρgas / ρair (3) where SG = specific gravity of gas ρgas = density of gas (kg/m3) ρair = density of air (normally at NTP 1.205 kg/m3) NTP Normal Temperature and Pressure defined as 20oC (293.15 K, 68oF) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 30 in Hg, 760 torr) Molecular weights can be used to calculate Specific Gravity if the densities of the gas and the air are evaluated at the same pressure and temperature. Sponsored Links
Concrete crushing machine Strong crushing ability, Low cost, High capacity &durable.Top service Related Topics Basics Basic Information as SIsystem, Unit converters, Physical constants Fluid Mechanics The study of fluids liquids and gases. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time. Mechanics Kinematics, forces, vectors, motion, momentum, energy and the dynamics of objects Beams and Columns Deflection and stress, moment of inertia, section modulus and technical information of beams and columns Material Properties Material properties density, heat capacity, viscosity and more for gases, fluids and solids Statics Loads force and torque
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Tag Search en: density specific weight gravity mass slugs pounds es: densidad de peso específico babosas masa gravedad libras de: Dichte spezifische Gewicht der Schwerkraft Masse Schnecken Pfund
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Density, Specific Weight and Specific Gravity
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Density, Specific Weight and Specific Gravity liters in3 ft 3 us gal
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Density, Specific Weight and Specific Gravity
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