6. Arcs

The principle of arcs is mostly used in character animation, but can be applied to any kind of animated element. With very few exceptions, all movement follows an arc or circular motion. Pay attention to the movement of your arm when you’re picking something up, or the movement of someone’s leg when walking, and you will see they follow a circular motion. Our body, and the body of other living creatures, consists of extremities connected to joints that constrain them to move in an arc. For this reason, making sure that your animated elements follow arched lines will create better flowing and more natural looking animations.

Even when objects could be moving in a straight line, we can make use of arcs to exaggerate an action and add personality to a scene. Arcs also help to keep your proportions constant from frame to frame. Here is an example:

The pendulum on the left looks wrong because its movement doesn’t follow an arc, so the “rope” seems to change length as the animation progresses.