Properties of Fluids in Fluid Mechanics

Mass density (ρ)

Mass density defined as the ratio of the mass of fluid to the volume of fluid. The density of liquids taken as constant while the density of gases changes with pressure and temperature.
Mass density, ρ=(Mass of fluid)/(Volume of fluid)=m/V

The SI unit of density is kg/m³
Dimensionally, ρ = ML^-3

Weight density/ specific density (w)

It is defined as the weight per unit volume. Mathematically,
Specific density, w= (Weight of fluid)/(Volume of fluid)=mg/V=ρg

Here ρ = mass density and g = acceleration due to gravity.
The unit of specific density is N/m³
Dimension, w=(MLT^(-2))/L^3 =ML^(-2) T^(-2)

Specific volume

The volume of fluid occupied by unit mass. It is reciprocal of density.

Dimension: M^-1L³

Specific gravity (s)

Also known as the relative density. It is defined as the ratio of the density of the fluid to the density of the standard fluid. In case of liquid the standard fluid taken as water and for gases it is air
Specific gravity= (Density of fluid)/(Density of standard fluid)

Specific gravity= (Density of fluid)/(Density of standard fluid)

It is a dimensionless quantity.

Viscosity (dynamic viscosity, µ)

It is defined as the property of a fluid that offers resistance to the fluid flow.

From newton’s law of viscosity, μ=τ/(du⁄dy)

Dimension, µ = ML^-1 T^-1

Kinematic viscosity (ν)

It is defined as the ratio of dynamic viscosity to the density of the fluid.
ν= (Dynamic viscosity)/Density= μ/ρ Dimension,ν= (ML^(-1) T^(-1))/(ML^(-3) )= L^2 T^(-1)

- Types of Fluids
- Types of Fluid Flow