Rules of animation; Slow in slow out, Arcs and secondary action

Slow in Slow out

Slow in slow out is the principle that the actions of an object or the actions of a human body, need time to accelerate and to slow down as well. This has meant that more realistic animations have more drawings at the beggining and the end of an action, this emphasizing the extremes of the action. This can be seen in the following image

http://www.animationbrain.com/stretch-squash-animation-principle.html

Arcs

arcs is the principle that most natural movements follow a more arched path, with more mechanical movements following a more straight paths (this being the exception to the principle). Arcs can be used to determine the speed of an object, if a ball is thrown then the straighter its arc to its target is the faster speed. A slow ball will need to be given more height so in turn will have a more curved arc.


Secondary Action

This is the process in which secondary actions are added to the animation in order to make an animation look more natural. This is applied alot to characters in cartoons where the character may whistle while walking or swing their arms, all in the hope of making a more fluid life like animation.