Answer:

Friction depends on the nature of the two surfaces. It depends on smoothness or roughness of the two surfaces which are in contact of each other. When two surfaces are in contact are smooth, then the friction between them is small because the interlocking of smooth surface is less.

Answer:

(d) depends on situation

Explanation:

Friction force opposes the relative motion between two surfaces in contact. If two surfaces are rubbed with a small force then simply the opposing force would also be small, but if they are rubbed with a stronger force then friction force will try to oppose the force involved. Hence, it would be higher.