Define fluid.

A fluid is a substance that deforms continuously under the application of shear stress no matter how small the shear stress may be. A fluid may be classified as:

• Liquid 

• Gas

• Vapour

Ideal Fluids:

An ideal fluid is one which has no viscosity and surface tension and is incompressible. In true sense, no such fluid exists in nature. However fluids which have low viscosities such as water and air can be treated as ideal fluids under certain conditions.

Real Fluids:

A real practical fluid is one which has viscosity, surface tension and compressibility in addition to the density. The real fluids are actually available in nature.

A fluid is a substance that deforms continuously under the application of shear stress no matter how small the shear stress may be. A fluid may be classified as:

• Liquid 

• Gas

• Vapour

Ideal Fluids:

An ideal fluid is one which has no viscosity and surface tension and is incompressible. In true sense, no such fluid exists in nature. However fluids which have low viscosities such as water and air can be treated as ideal fluids under certain conditions.

Real Fluids:

A real practical fluid is one which has viscosity, surface tension and compressibility in addition to the density. The real fluids are actually available in nature.