### Fluid and some of its properties.

A fluid may be defined as a substance which deforms continuously when subjected to a shear stress or in other words a fluid is a substance which cannot withstand shear stress. Fluid mechanics deals with the behavior of fluids at rest and in motion. Fluids may be of liquid or gaseous forms. Liquid is practically incompressible and occupy definite volume and have free surfaces. Whereas, gaseous fluids are compressible. Gases can expand until it occupies all portion of any containing vessel.

## Properties of fluid:

Important fluid properties are mentioned below

### Mass Density, ρ:

It is the mass per unit volume. The density of water at standard temperature and pressure is 1000 kg/m3 .

### Specific volume Vs :

It is the volume occupied by unit mass of fluid i.e. specific volume is the reciprocal of density. Therefore, Vs = 1/ρ.

### Specific weight, ɣ :

Specific weight may be defined as the weight of a unit volume of a substance. For water at standard conditions specific weight is equal to 9.81 kN/m3 . The relation between specific weight and density can be written as ɣ = ρg.

### Viscosity, µ:

Viscosity may be defined as the property of a fluid which determines the amount of its resistance to a shearing stress.
The viscosity of a liquid decreases with the increase of temperature due to decrease of molecular cohesion between molecules and this is responsible for reduction in liquid viscosity. But is case of gas viscosity increases with the increase of temperature due to greater molecular activity as the temperature increases.

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