Ease In and Ease Out
'Ease In and Ease Out' (or 'Slow In and Out') is a principle of animation which gives the effect of cushioning motion, as opposed to bringing it to a sudden halt or an unrealistic jump-start.
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​In real life, humans, animals and vehicles will accelerate before reaching full action speed and decelerate before coming to a standstill. Even with plain shapes like circles and squares, it is evident that slowing in and out starts to give some illusion of life. The softening effect is also easy on the eye, much more satisfying than the robotic alternative.




These animations show the effect that spacing can give. Compared to the exact same timing of moving an object from A to B without any particular spacing in mind, the slowing pace makes a more realistic movement.
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As described earlier with the bouncing ball example, the amount of drawings indicates the speed of an action. When many drawings are bunched together at the end/beginning of an action, it gives a cushioning effect similar to a pendulum as it reaches its point of return.​

There are many ways to implement easing in and out with character movement. In full body action, for instance somebody might get out of a chair slowly and sit down again slowly. The same idea applies to a head turn, an arm gesture, or any body part in motion which can be much more convincing with a subtle approach to easing in and out.
