Law of Limiting Friction is: (1) The force of Limiting Friction is directly proportional to normal reaction and it takes place in direction which is opposite to the direction of the force of pull. Limiting Friction is maximum static friction. i.e., F ∝ R ⇒ F = µR. Where µ is the coefficient of friction. (2) Limiting Friction is independent of the size and shape of the surface in contact as long as the normal reaction remains the same.