Which of the following statements regarding laws governing the friction between dry surfaces are correct?
(a) The friction force is directly proportional to the normal force.
(b) The friction force is dependent on the materials of the contact surfaces.
(c) The friction force is independent of the area of contact.
(d) all of the mentioned
This question was addressed to me in an interview for job.
The above asked question is from Coefficient of Friction topic in section Friction of Machine Kinematics