Squash and Stretch

The Squash and Stretch principle is the techinque of squashing and stretching animated objects in motion to enhance the illusion that an animated object has weight and flexibility.

The most well known demostration of this techinque is the bouncing ball (the example drawn below is not that good (I admit)).

The effect is well observed in real life when you look at objects colliding or been dropped and on to a surface.

The folowing link is to a high speed video clip of a golf ball been hit by the club, clearly showing the squash and stretch principle in the real world.
http://www.youtube.com/watch?v=2Y57pw_iWlk&NR=1

In this drawing of a paino hitting the ground, the squash and stretch principle is applied (notice the bending of some parts of the piano).

The principle can also be applied to the muscles of moving limbs. In living organisms, arms and legs are moved by a pairs of muscles. When an arm or leg bends, one muscle contracts (squashing) while the other relaxes (stretches).