Question

There are two surfaces, A and B in contact with each other. Consider the following situations:

Situation I: Both A and B are at rest.
Situation II: A is moving while B is at rest and A is over B.
Situation III: A is at rest while B is moving and A is over B.
Situation IV: A is at rest while B is moving and B is over A.

In which of the given situations would you expect frictional force to come into play?

• A. Situation I
• B. Situation II
• C. Situation III
• D. Situation IV

Answer 1

Answer: (B), (C), (D)

The correct options are
B

Situation II

C

Situation III

D

Situation IV

We know that friction opposes relative motion. This means that for friction to come into play, there should be relative motion and hence in situations II, III and IV, friction would be there. Having relative motion is independent of which surface lies over the other.