# Viscosity and Coefficient of Viscosity

## Viscosity and Coefficient of Viscosity

Viscosity is a property of liquid which resist to flow. Due to viscosity some liquid flow slowly and some liquid flow quickly. Viscosity is nothing but internal reistance to flow possessed by liquid.Liquids which flow slowly, have high internal resistance which is due to strong intermolecular forces says more viscous or are of high viscosity.

However, Liquids which flow rapidly have low internal resistance which is due to weak intermolecular forces says less viscous or are of low viscosity.

Greater are the intermolecular forces, higher is the viscosity of the liquid. Viscosity decreases with increasing the temperature. Kinetic energy increases on increasing temperature and so intermolecular force of attraction decreases, consequently, viscosity decreases and liquid flow quickly.

We know that liquid flow in layers in a tube. Liquid that contact in the surface of tube is almost stationary. As we move from the surface towards the centre of the tube, the velocity of the liquid layers keeps on increasing till it is maximum at the centre.

The force of friction F between two layers each having area A cm

^{2}, separated by a distance dx cm , and having a velocity difference of dv cm/sec ,is given by-

F ∝ A ( dv / dx )

F = η A ( dv/dx)

where η is coefficient of viscosity.

dv / dx is viscosity gradient

If dx = 1cm, A = 1cm

^{2}and dV = 1cm/sec

F = η

**Coefficient of viscosity**may be defined as the

__force of friction required to maintain a velocity difference of 1 cm/sec between two parallel layers, one centimeter apart and each having an area of one square centimeter__.

The unit of viscosity are dynes sec cm

^{-2}.This is also called 1 Poise.