Question

Limiting friction is also called as…….
A. maximum value of friction
B. least value of friction
C. none
D. both

Answer 1

Hint the maximum static friction that a body can exert on the other body in contact with it, is called limiting friction. This limiting friction is proportional to normal contact force between the two bodies. We can write,
\[{f_{\max }} = {\mu _s}{\rm N}\]
Where, \[{f_{\max }}\] is the maximum possible of static friction.
And, ${\rm N}$ is normal force.

Complete Step by step solution
The amount of friction that can be applied between two surfaces is limited and if the forces acting on the body are made sufficiently great; the motion will occur. Hence, we can define limiting friction as the maximum value of static friction that comes into play when the body is just at the point of sliding over the surface of another body. Limiting friction is the product of normal force and coefficient of limiting friction. Mathematically, this is represented as
\[{f_{\max }} = {\mu _s}{\rm N}\]
Here, ${\mu _s}$ is constant of proportionality and is called the coefficient of static friction and its value depends on the material and roughness of the two surfaces in contact. In general, ${\mu _s}$ is slightly greater than ${\mu _k}$ i.e., coefficient of kinetic friction.
Now as long as the normal force is constant, the maximum possible friction does not depend on the area of the area of the surfaces in contact.
Once again, we emphasize that \[{\mu _s}{\rm N}\] is the maximum possible force of static friction that acts between the bodies. The actual force of static friction may be smaller than \[{\mu _s}{\rm N}\] and its value depends on the other forces acting on the body. The magnitude of frictional force is equal to that required to keep the body at relative rest. Thus,
${f_s} \leqslant {f_{\max }} = {\mu _s}{\rm N}$
The limiting friction is always opposite to the motion of the object.

Hence option (A) is correct.

Note Static friction is a self-adjusting force because it comes into play when the body is lying over the surface of another body without any motion. If we have not applied any force on a body to move the body, the frictional force also becomes zero. If we start applying force, with the applied force, the frictional force also starts increasing. This happens until the applied force is less than limiting frictional force. When that body overcomes the force of static friction, the maximum value of static friction is reached -which is known as limiting friction. After the limiting friction, the frictional force is not going to increase further. At this stage, the object moves overcoming the frictional force which is at a constant value. This is called kinetic friction.