Question

Friction depends on the _________ of surfaces.

Answer 1

Hint Friction is the force which opposes the relative motion. When a body is placed on a ground, it presses the ground with some force ( also known as weight ) which is due to gravity and friction depends on the forces by which two bodies hold each other and the roughness coefficient of bodies.

Complete step by step answer:
Friction is greater means two bodies are holding each other with greater force. In other words, those two bodies will oppose their relative motion with more force.

Now suppose, two bodies of mass $m$ and $10m$ with the same roughness are placed on a rough floor and you are to slide both bodies. Obviously a body with mass $10m$ will be harder to slide than a body with mass $m$ .
Hence friction also depends on the mass of bodies.

Now suppose, two bodies of mass $m$ and $m$ with one body having greater roughness than the other body placed on a rough place. You are also asked to slide both bodies. You should be having greater force to move your body with greater roughness.
Hence friction also depends on the nature of bodies.
Hence, friction depends both on the nature of bodies and the mass of bodies.

Let the roughness of the place on which a body of mass $m$ is moving is given by $\mu$ and Earth’s gravity is $g$ then friction force acting on the body in opposite motion will be given by
$F = \mu mg$

Hence, it also shows that friction depends on mass and nature (roughness) of bodies.

Note It is not the fact that greater the surface area in contact between bodies moving in a relative opposite motion, greater will be the friction force opposing their relative motions. Friction also increases if the bodies are extremely smooth because attractive electrostatic force between atoms of surfaces of both bodies increases.