Question

If ${\mu _k}$ is coefficient of kinetic friction and ${\mu _S}$ is coefficient of static friction, then
A. ${\mu _k} < {\mu _S}$
B. ${\mu _S} < {\mu _k}$
C. ${\mu _k} = {\mu _S}$
D. ${\mu _k} \le {\mu _S}$

Answer 1

We will use the concept of friction acting between the surface of a body and the surface on which it is moving when the body is in static condition and motion. The coefficient of friction gives us the relationship between the friction force, and it’s normal.

Complete step by step answer:
When a body moves or tends to move, a force develops at the rough contact surface called friction force or only friction. This force always acts opposite to the direction of motion of the body. The friction that keeps a body in the static condition is called static friction. This value of friction has to be overcome by an energy that is used to move the body. Due to the presence of irregular surface and charge between the body and surface molecules, a more significant amount of energy is required to move the body initially than required to keep it in motion.
The ratio of the maximum value of static frictional force when the body is about to move, and the normal force is called a coefficient of static friction. Whereas when the body is in motion, the ratio of friction force and normal force is called a kinetic friction coefficient.
Therefore, we can say that the coefficient of static friction is more than the coefficient of kinetic friction

So, the correct answer is “Option A”.

Note:
Friction force has a remarkable property of adjusting itself in magnitude to the applied force. But there is a limit beyond which it cannot be increased. The maximum value friction force comes into play when motion is impending, and it is called limiting friction force.