Fluid Mechanics-Properties of Fluids

Fluid mechanics

Fluid mechanics is defined as the science that deals with a fluids behaviour,when it is at rest or motion and fluids interaction with other solids or fluids.Here we talking about fluid mechanics and Properties of Fluids

Fluid dynamics deals with the study of fulids in motion and the study of incompressible fluids under static condition is called hydrostatic

liquids and gases are commonly fluids.A fluid is defined as a substance that deforms continuously under the influence of a shear stress of any magnitude ie when subjected to an external force of any magnitude

Properties of Fluids

Properties of Fluids


Density is defined as mass per unit volume .If m is the mass of the fluid body and it occupies a voulume V


Density = Mass/Volume

Eg:The density of water at 4 degree celcius is 1000kg/m³

2.Specific Volume

Specific volume is defined as volume per unit mass.The reciprocal of a fluids density (ρ) is its specific volume (ν)

That is

      ν = 1/ρ = V/m 

        The SI unit of specific volume is m³/kg

3.Specific Weight

 Specific weight is defined as the weight per unit volume

 ie Specific weight= ω =W/V = mg/V = ρg

 where g is the acceleration due to gravity

             W= Weight of the substance

             V=Volume of the substance

 4.Specific Gravity

 Specific gravity of a fluid is the ratio of the density of the fluid to the density of the standard fluid.The standard fluid is taken to be pure water at 4 degree celcius.

Specific Gravity of a fluid = ρ fluid /ρ standard =   ω fluid / ω standard fluid


Viscosity is the property of the fluid by virtue of which it resists fluid flow. ie viscosity represents the internal resistance of a fluid to motion or to shearing stress.

The SI Unit of viscosity is kg/ms or Ns/m²

Another unit for viscosity in poise is =0.1 Ns/m²

Viscosity of water for practical calculations is taken to be 1 centipoise or 0.01 poise

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