Squash and Stretch/Timing

Squash and stretch is a common animation technique applied to characters or machinery in motion.  giving it a cartoonish feel as opposed to realistic jumping motion.When real objects move only totally rigid ones, e.g., a chair, remain rigid in motion. Living creatures always deform in shape in some manner. For example, if you bend your arm, your bicep muscles contract and bulge out. They then lengthen and disappear when your arm straightens out. The squashed position shows the form flattened out and the stretched position shows the form extended. An important rule is that the volume of the object should remain constant at rest, squashed, or stretched. If this rule is not obeyed, then the object appears to shrink when squashed and to grow when stretched.

A classic example is a bouncing ball, that squashes when it hits the ground and stretches just before and after. The stretching, while not realistic, makes the ball appear to be moving faster right before and after it hits the ground, which can be seen here in this video: