Question

Identify the direction of the friction force in the following cases:

(a) a book sitting on a table
(b) a box sliding on a horizontal surface
(c) a car making a turn on a flat road
(d) the initial conveyor motion of a machine delivered on a conveyor belt in an assembly line

Answer 1

(a) no frictional force is acting on the book. there is only gravity downward and a normal force upward.

(b) frictional force due to surface. this force acts in the opposite direction of motion.

(c) force is allowing the car to undergo circular motion. this centripetal frictional force must act inwards towards the center of the circle of motion.

(d) frictional force due to the gears controlling the conveyor belt. in this case, the frictional force is what drags the conveyor belt along, so this frictional force acts in the same direction as the motion.

Answer 2

so, in letter a, since there is no frictional force, therefore there is no direction for friction?