Principles of Animation
Definitions:
Squash and Stretch - The most important principle is "squash and stretch", the purpose of which is to give a sense of weight and flexibility to drawn objects. It can be applied to simple objects, like a bouncing ball, or more complex constructions, like the musculature of a human face.
Arcs - Most natural action tends to follow an arched trajectory and animation should adhere to this principle by following implied "arcs" for greater realism.
Straight Ahead and Pose to Pose - These are two different approaches to the actual drawing process. "Straight ahead action" means drawing out a scene frame by frame from beginning to end, while "pose to pose" involves starting with drawing a few key frames, and then filling in the intervals later.
Slow In and Slow Out - The movement of the human body, and most other objects, needs time to accelerate and slow down. For this reason, animation looks more realistic if it has more drawings near the beginning and end of an action, emphasizing the extreme poses, and fewer in the middle.
Definitions:
Timing - Timing refers to the number of drawings or frames for a given action, which translates to the speed of the action on film.
Exaggeration - Exaggeration is an effect especially useful for animation, as perfect imitation of reality can look static and dull in cartoons.
Anticipation - Anticipation is used to prepare the audience for an action, and to make the action appear more realistic.
Staging - Its purpose is to direct the audience's attention, and make it clear what is of greatest importance in a scene.
Definitions:
Appeal - Appeal in a cartoon character corresponds to what would be called charisma in an actor. A character who is appealing is not necessarily sympathetic – villains or monsters can also be appealing – the important thing is that the viewer feels the character is real and interesting.
Solid Drawing - The principle of solid drawing means taking into account forms in three-dimensional space, or giving them volume and weight.
Secondary Action - Adding secondary actions to the main action gives a scene more life, and can help to support the main action. A person walking can simultaneously swing his arms or keep them in his pockets, speak or whistle, or express emotions through facial expressions. The important thing about secondary actions is that they emphasize, rather than take attention away from the main action.
Follow Through and Overlapping Action - A general heading for two closely related techniques which help to render movement more realistically, and help to give the impression that characters follow the laws of physics, including the principle of inertia. "Follow through" means that loosely tied parts of a body should continue moving after the character has stopped and the parts should keep moving beyond the point where the character stopped to be "pulled back" only subsequently towards the center of mass and/or exhibiting various degrees of oscillation damping. "Overlapping action" is the tendency for parts of the body to move at different rates (an arm will move on different timing of the head and so on). A third, related technique is "drag", where a character starts to move and parts of him take a few frames to catch up.
