Arcs...
...are the unseen circular paths of action. If movement happens outside of the arc, it will appear unnatural. It generally applies to limbs, joints and objects travelling through the air. They're organic, expressive movements. Before this principle was developed actions were far more mechanical and linear. In the contemporary examples directly below we see Spongebob create an arc with his hands, that is then mapped out by a rainbow - quite helpfully. The clip beside it illustrates the nature of arcs within a secondary action. Angelina Ballerina, famous for twirling ribbon, generates sequential circular motion through directional force. If the ribbon moved in a linear motion, there would be a severe lack of realism.
The Tasmanian Devil is infamous for his use of arc movement. Not only is he a constant display of this principle, but motion lines are even employed to illustrate it.
Written by Madeleine Grossi