Viscosity Explanation in Property of Matter - QS Study
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Viscosity Explanation in Property of Matter

Viscosity is a special property of matter. Only liquids and gases have this property. So, it is the general property of liquid and gaseous materials. But our point of discussion is to know what type of property this one is.

If a fluid flows in streamline motion on a fixed horizontal surface, the layer that is far away from the stationary surface has higher velocity and the layer which is adjacent to the stationary surface has zero. Suppose AB is the stationary surface A fluid is moving through it in stream-line motion PQ, CD and EF are three layers of the fluid (Figure). PQ is adjacent to the stationary surface. CD is slightly away and EF is far away.

Among them, velocity of EF is more, velocity of CD is smaller than that of EF and the velocity of PQ is zero. This is because that upper layer tries to drag the lower layers along with it with equal speed. That means, along with forward motion of the fluid there develops an internal force between the two layers. This force tries to decrease the speed of the layer which has higher speed and increase the laver which has lower speed and thus tries to decrease the relative speed between the two lavers. The force acting parallel to the surface of the two layers is called viscous force and this property of the fluid is called viscosity.