Learn : Definition of fluid,liquid ,gas,vapour,ideal fluid,practical or real fluid,what is a fluid,what is a fluid give example,is liquid is fluid, what is fluid and its classification.

## DEFINITION OF  FLUID

What is fluid and its classification?

A fluid is defined as a substance which is capable of flowing.

It has no definite shape of its own, but conforms to the shape of the containing vessel.

Further, even a small amount of shear force exerted on a fluid will cause it to undergo a deformation which continues as long as the force continues to be applied.

### A liquid

A liquid is a fluid, which possesses a definite volume, which varies only slightly with temperature and pressure.

Since under ordinary conditions liquids are difficult to compress, they may be for all practical purposes regarded as incompressible.

It forms a free surface or an interface separating it from the atmosphere or any other gas present.

### A gas

A gas is a fluid, which is compressible and possesses no definite volume, but it always expands until its volume is equal to that of the container.

Even a slight change in the temperature of a gas has a significant effect on its volume and pressure.

However, if the conditions are such that a gas undergoes a negligible change in its volume, it may be regarded as incompressible.

But if the change in volume is not negligible the compressibility of the gas will have to be taken into account in the analysis.

### A vapour

A vapor is a gas whose temperature and pressure are such that it is very near the liquid state.

Thus steam may be considered as a vapor because its state is normally not far from that of water.

The fluids are also classified as ideal fluids and practical or real fluids.

### Ideal fluids

Ideal fluids are those fluids which have no viscosity and surface tension and they are incompressible.

As such, for ideal fluids no resistance is encountered as the fluid moves.

However, in nature the ideal fluids do not exist and therefore, these are only imaginary fluids.

The existence of these imaginary fluids was conceived by the mathematicians in order to simplify the mathematical analysis of the fluids in motion.

The fluids which have low viscosity such as air, water, etc., may however be treated as ideal fluids without much error.

### Practical or real fluids

Practical or real fluids are those fluids which are actually available in nature.

These fluids possess the properties such as viscosity, surface tension and compressibility and therefore a certain amount of resistance is always offered by these fluids when they are set in motion.

(i) Alluvial soils.

These soils are formed by deposition of water borne materials. It is a very fertile type of soil for crops.

(ii) Residual soils.

These soils are the resultant of disintegration of rocks under various natural actions.

(iii) Volcanic ash.

These soils are formed by deposition of Volcanic Ash from volcanic eruptions. (iv) Glacial soils. These soils are formed by transportation and deposition by glaciers. (v) Eolian soils. They are the resultant of deposition by wind action.

(vi) Colluvial soils.

They are formed as a result of deposition by rainwash below foot hills. (vii) Aggradation soils. They are the accumulation soils.