Which combination of the above is true of sliding friction?

I. The frictional force is independent of the area of the surfaces in conduct
II. The frictional force depends on the nature of the surfaces in contact
III. The frictional force depends on the speed of sliding
IV. The frictional force is directly proportional to the normal reaction.

A. I, III and IV
B. I, II and IV
C. I, II and III
D. II, III and IV

Correct Answer:

Option B – I, II and IV