(a) The motion of the swimmer is not regular. A swimmer’s move between the sides of a river is to and fro. It does not, however, have a set duration. This is because the swimmer’s back and forth voyage may not take the same amount of time.

(b) When a freely suspended magnet is displaced from its N-S direction and released, it moves in a predictable pattern. Because the magnet rotates around its axis over a set amount of time.