Viscosity
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Viscosity :

It is the property of matter which tends to prevent motion of one part over another.

It is the property that the fluid resists its flow.

It is the property that the fluid resists the flow of solid in it.

Experiments to show viscosity:

1.      On putting water on a horizontal surface, the water spreads out rapidly on the hand, Glycerin does not spread out rapidly.

2.      On stirring liquids for a certain interval of time, highly viscous liquid show high resistance to motion (honey) & they soon come to rest.

3.      Let two similar steel balls are left to sink in two similar jars filled with water & Glycerin respectively.

The steel ball in the Glycerin jar takes a longer time to reach the bottom therefore Glycerin is more viscous than water.

Explanation of viscosity

 ·          If we divided the liquid between two parallel plates into horizontal layers.

·          One plate is at rest & the other moves with velocity “V”.

·          Between the two plates the liquid moves with different velocities ranging from zero at the lower plate up to “V” at the upper one.

·          The relative change of velocity is due to:

1.         A friction force between the plane surface of the lower plate & the liquid layer in contact with it (this is due to adhesive force between the molecules of the solid surface & contacting liquid molecules).

So, the velocity of  the layer in contact with rest plate is zero, the velocity of layer in contact with moving plate is “V”.

2.         Another force to friction force between each liquid layer & the adjacent one which resists the sliding of the liquid layer over each other this produces a relative change in velocity between any two adjacent layers.