Question

The tangential force or viscous force on any layer of the liquid is directly proportional to velocity gradient $\left(\frac{dv}{dx}\right)$. Then the direction of velocity gradient is :

• A. perpendicular to the direction of flow of liquid.
• B. parallel to the direction of flow of liquid.
• C. opposite to the direction of flow of the liquid.
• D. independent of the direction of flow of liquid.

Answer 1

The correct option is A perpendicular to the direction of flow of liquid.

According to question tangential force, $F_T\propto \frac{dV}{dX}$
Now, because of viscous force, liquid which is in contact with the surface does not move and the liquid of the top layer moves with greater velocity, so there is velocity change in vertical direction. Thus $\frac{dV}{dX}$ is perpendicular to the direction of flow of liquid.