Arcs

Arcs in animation are used all the time in all actions, with few exceptions such as movements of a mechanical device. They are movements which follow an arc even a circular path or curves. Also, they give a natural feel and better flow to the animation.

This diagram shows a bouncing ball and the semi-circular path that follows.

Arcs in walk cycles. This picture shows different arcs in an action. First, it is the head and the main body, and its hand moving in front and back.