SOLUTION

The coefficient of friction is the ratio of limiting frictional force F to the normal reaction R between the two surfaces. It is denoted by µ.

µ = F/R

The coefficient of friction is of three types namely coefficient of static friction µ_s, coefficient of kinetic or dynamic friction µ_k, and coefficient of rolling friction µ_r.

(i) For the same two surfaces, µ_s > µ_k> µ_r

(ii) Limiting friction is the maximum value of static friction.

(iii) The force of friction always acts parallel to the surfaces in contact.

(iv) The force of friction F is equal to applied force if it is less than or equal to µ_r.