Question

The static friction

(a) bears a constant ratio to the normal reaction between the two surfaces

(b) is independent of the area of contact, between the two surfaces

(c) always acts in a direction, opposite to that in which the body tends to move

(d) all of the mentioned

I got this question during an interview for a job.

Query is from Friction of Pivot and Collar Bearing in division Friction of Machine Kinematics

Answer 1

Right choice is (d) all of the mentioned

Easy explanation: The laws of static friction are:

a) The force of friction always acts in a direction, opposite to that in which the body tends to move.

b) The magnitude of the force of friction is exactly equal to the force, which tends to move.

c) The force of friction is independent of the area of contact, between the two surfaces.

d) The force of friction depends upon the roughness of the surfaces.