Question

What kind of friction comes into play:
(a) when a block of wood kept on table moves slowly?
(b) when a block of wood kept on table just tends to move (or slip)?
(c) when a block of wood kept on cylindrical iron rods moves?

Answer 1

A) When the block moves horizontally, there is kinetic (dynamic) friction that comes into play.

b) When a block of wood kept on table just tends to move or slip, from initial rest position, then static friction comes into play. This friction is more than dynamic friction.

c) A block is kept on a set of cylindrical rods. The rods rotate and so the block moves horizontally. Then rolling friction comes into play. This kind of friction is less than the other two types.