Prove that the force of friction depends on the nature of two surfaces in contact.
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. When two surface is rough then the friction is more because the interlocking is very strong in very rough surface.