| 1.Co-efficient of Viscosity:
Let us consider a horizontal flow of fluid between two side walls and it is similar to a water flowing through a canal. Let the flow of fluid be streamline. In such case, the fluid in contact with the fixed surface, i.e., side walls is stationary and as we move away from side walls, the velocity of fluid increases. Thus, as we move perpendicular to the direction of flow, we encounter different layers of fluid with different velocity and that is shown in Fig1. The length of arrows indicates the magnitude of velocity at different positions. |
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Let us consider two neighboring layers of liquid with velocity vn and vn+1 as shown in Fig. 1. It is clear from the figure that vn+1>vn. Because of the greadient in velocity, nth layer tends to retard the (n+1)th layer and on the other hand (n+1)th layer tends to accelerate the nth layer. As a result, these two layers tend to reduce their relative velocity and it is equivalent to a backward dragging force. This type of dragging force is similar to the frictional forces, in solids. In the absence of any external force, the flow of fluid would cease due to the above dragging force. The property of the fluid, which opposes the relative motion between its layers is called VISCOSITY. Thus the backward dragging force is called viscous force.
The viscous force is directly proportional to the velocity gradient of fluid layers perpendicular to fluid flow direction and the contact area of layer. |
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