Ease in and Ease out

Humans are used to thinking of slow moving rivers and tides that ease in and ease out.

人类习惯了认为河流和海潮是缓慢运动的，悠闲地来来去去。

As it goes up, gravity affects it and slows down (Ease In), then it starts its downward motion more and more rapidly (Ease Out), until it hits the ground.

当他上升时，重力影响它使它变慢(缓入)，然后开始下降时动作就越来越快速(缓出)直到它弹跳到地面。

For snappy cartoon motion, you may have ease in and out over only a couple of frames. But even 3 frames of ease in and out may help a limb from looking too stiff or mechanical.

卡通类型的动作里你只要2帧来做这个渐变过程就可以，但如果是用3帧来做，看上去就会比机械的僵硬的动作好很多。