Question

The limiting value of static friction between two contact surfaces is:
(A) Proportional to normal force between the surfaces in contact.
(B) Independent of area of contact
(C) Depends on the microscopic area of constant magnitude.
(D) All of the above

Answer 1

Hint
We know that friction is a force between two surfaces that are sliding or trying to slide across each other. For example, when you try to push a book along the floor, fiction makes it difficult. Friction always works in the direction opposite to the direction in which the object is moving or trying to move. We can also say that friction is a force which is resisting the relative motion of solid surfaces, fluid layers and material elements sliding against each other. Based on the concept we have to solve this question.

Complete step by step answer
Static friction is defined as a force that keeps an object at rest. Static friction can also be written as the friction which is experienced when individuals try to move a stationary object on a surface without actually triggering any relative motion between the body and the surface which is on it.
We can write the formula of static friction as,
 $ {{F}_{0}}={{\mu }_{s}}N $
Hence, we can see from the equation that N being the normal force between the points of contact, is directly proportional to the value of static friction $ {{F}_{0}} $ where $ {{\mu }_{s}} $ is the static frictional constant. Therefore, it determines the fact that the limiting value of static friction is not independent of the area of contact, neither it depends on the microscopic area of constant magnitude.

Therefore, the correct answer is Option (A).

Note
We know that the force of static friction can be calculated by taking the coefficient of friction between the two surfaces and multiplying it by the normal force that the surface is applying to the object. On a flat surface, the normal force is equal to the force of gravity acting down on the object.
The coefficient of dynamic friction is the force between two objects when one object is moving, or if objects are moving against one another. Angle of repose is defined as the angle of the inclined plane with horizontal such that a body placed on it just begins to slide.