State the laws of friction.

Explanation

`(a)` Limiting friction depends on the nature of the surfaces in contact but not on the surface area as long as normal reaction remains the same.
`(b)` Force of friction always acts tangential to the surface and opposite the direction of motion.
`(c )` The limiting friction is directly proportional to the normal reaction between two surfaces in contact.
`(d)` The kinetic friction becomes constant, once there is a realtive motion between the two surfaces.
`(e) mu_(s) gt mu_(k) gt mu_(r )` where `mu_(s),mu_(k)` and `mu_(r )` are coefficient of friction due to static friction, kinetic friction and rolling friction respectively.