Question

In which of the following option(s) frictional force exists?

• A. A boulder rolling down a mountain
• B. Airplane flying
• C. A swimmer in river
• D. None of these

Answer 1

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

The correct options are
A

A boulder rolling down a mountain

B

Airplane flying

C

A swimmer in river

Friction is present whenever there is contact between two solid surfaces or a solid surface and a fluid. In all the options some friction is experienced as there is some contact in all the cases. But when the moon is revolving around the earth there is no contact between the surfaces of the moon and the earth. Also, the moon orbits in space where there is a vacuum. Hence, no frictional force is involved in this case.