Squash and stretch give animated objects the illusion of weight and volume

Squash and stretch is the most fundamental of the 12 Disney animation principles: when an object moves, it deforms in the direction of motion (stretching at high speed) and compresses on impact or at maximum velocity change (squashing). This deformation signals mass and elasticity — a rubber ball squashes on landing and stretches on bounce, while a rigid object barely deforms. The magnitude of squash and stretch signals material properties: rubber stretches dramatically, wood barely at all. In generative animation, applying squash/stretch to a bouncing element means scaling X and Y inversely as the velocity changes. Without it, even physically accurate trajectories look mechanical; with it, even simple shapes feel alive.

Examples

A bouncing circle: at peak height scale is 1:1; as it falls and accelerates, stretch vertically (1.0 × 1.3); on impact, squash horizontally (1.3 × 0.7). The volume (area) stays approximately constant. In p5.js: ellipse(x, y, w * squashX, h * squashY) where squashX and squashY are inversely related.

Assessment

Explain what happens to the scale of a bouncing ball at peak height, during fall, and on impact, in terms of squash/stretch. Then name one other object type where exaggerated squash/stretch would look wrong, and explain why.