Viscosity: Coefficient and effect of temperature and pressure

Viscosity :- The property of the fluids by which a backward dragging force acts tangentially on the layer of the fluid in motion and tries to stop the motion is known as Viscosity .

Cause of Viscosity :- Viscosity is caused due to the intermolecular forces , which are effective when the different layers of the liquid are moving with different velocities.

Coefficient of Viscosity :- The coefficient of Viscosity is denoted by η . 

It is defined as The tangential viscous force which maintains a unit velocity gradient between its two parallel layers on each of unit area .

Numerically , 

                              η ∝ F  

Effect of Temperature on Viscosity :-

1. On increase in temperature , the Viscosity of liquid is decreases i.e. Viscosity is inversely proportional to Temperature.
When a liquid is heated , the kinetic energy of its molecules increases and thus intermolecular attraction between them become weaker . Hence the Viscosity of a liquid decrease with increase in temperature.
2. Viscosity of a gas increases with temperature as :
The cause of Viscosity in gases is due to the diffusion of molecules from one moving layer to another . But the rate of diffusion of the gas is directly proportional to the square root of its absolute temperature.

Effect of Pressure on Viscosity :-

1. The Viscosity of all the liquids except water increases with increase in temperature . On the other hand , Viscosity if water decreases on increase in temperature.
2. The Viscosity of gases is independent of Pressure i.e. Pressure doesn't effect on Viscosity of gases .

This was introduction to Viscosity . Hope you liked it . Comment down your queries and any mistakes (if you found) .
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