Fluid and its type

Fluids undergo continuous deformation, i.e. fluids always keep flowing. To define fluid, it is a substance that does not possess a definite shape and easily yields to external pressure. Fluid is any liquid or gas or any material that is unable to withstand a shearing or tangential force, when at rest. When the said forces are applied to the fluid, it goes through a continuous change in shape. Fluids are substances with zero shear modulus, i.e they cannot resist the shear force applied to them.

In our day-to-today life, we would have heard the dehydrated patient advised to consume more fluids to compensate for the water loss. Fluids help in the digestion of food, hence we need to take more fluids.

Classification of Fluids

Fluids are classified into four types depending on its flow, they are:Steady or unsteady

Compressible or incompressible

Viscous or non-viscous

Rotational or irrotational

Steady fluid: It is the fluid whose density remains constant at each and every point while flowing.

Unsteady fluid: It is the fluid whose velocity differs between any two points while flowing.

Compressible fluid and incompressible fluids: These are classified based on the mach number. The incompressible fluid has mach number<0.3 and the compressible fluid has mach number between 0.3 and 1.

Viscous or Non-viscous

Fluids with more thickness or viscosity are known as viscous fluids, they are generally very gloppy fluids. Examples: shampoo and motor oil.

Fluids with comparatively less thickness or viscosity are known as non-viscous fluids. These are the fluids with no resistance or negligible resistance to internal friction. Non-viscous fluids flow without any loss of kinetic energy.

Example: Superfluid liquid helium