What is Density, Specific Weight, Specific Volume and Specific Gravity?

What is Density, Specific Weight, Specific Volume and Specific Gravity


What is Inside?

  • Density or mass density,
  • Specific weight,
  • Specific volume and
  • Specific gravity

Density or Mass Density: 

Density (mass density) of a fluid is defined as the ratio of mass of a fluid to the volume of the fluid. In other words it is defined as the mass per unit volume of a fluid.

Mass density (density) = mass/volume
ρ = m/V

Specific Weight:

Specific weight of a fluid is defined as the ratio of the weight of a fluid to the volume of the fluid. Or weight of a fluid per unit volume is called its specific weight.

Specific weight = (weight of fluid)/(volume of fluid)
w = mg/V = ρg

Specific Volume:

Specific volume of a fluid is defined as the ratio of the volume of a fluid to the mass of the fluid. In other words it may also be defined as volume per unit mass of a fluid.

Specific volume = (volume of fluid)/(mass of fluid)
specific volume = V/m  = 1/ρ

Specific Gravity:

Specific gravity is defined as the ratio of the density of a fluid to the density of a standard fluid. For liquids, water is taken as the standard fluid where as for gases air is taken as the standard fluid. It is denoted by the symbol S.

specific gravity, S = (density of liquid)/(density of water) 
                   = (density of gas )/(density of air)
  • The density of water is taken as 1000 kg/ cubic metre

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