12 Principles of Animation: Arcs

Arcing motion of hand

Most actions, except for some mechanical ones, revolve around some type of arcing motion. By adhering to this principle of movement, animators add an extra sense of reality in their animation by making characters move in a naturalistic manner. Arcs, for most of the time, are applied on limbs, which revolve around a pivot point during the movement of the character. Furthermore, the faster the action is, the flatter the arc becomes. In other words, if the movement is faster (during running, for an example) there are fewer frames exhibiting the arc. However, if the movement is slower (for example, an arching movement of a head turning), the arcs are gradually slower and contain more frames.

Scooby-Doo: https://www.youtube.com/watch?v=UtnPE1YRxfE

For example, during the 12:02 mark, Shaggy's walk is followed by an arcing movement of his arms, portraying a realistic and non-stiff motion of walking.