Question

In which of the following situations is frictional force acting?

• A. A rock rolling down a mountain
• B. An airplane flying in atmosphere
• C. A person swimming in river
• D. The Moon revolving around Earth

Answer 1

Answer: (A), (B), (C)

A person swimming in river

Frictional force is the opposing force which resists the relative motion between two solid surfaces, two fluid layers or a solid surface and a fluid layer. It can only act when there is physical contact between two surfaces. In all the situations except that of the Moon revolving around Earth, some friction is experienced as there is relative motion between two objects in contact. However, the Moon orbits Earth in space where there is a vacuum. Hence, no frictional force is involved in this case.