Editing Squash and stretch (section)

==Basis==
[[File:Muybridge race horse animated.gif|frame|Sequence of a race horse galloping animated from a [[chronophotography]] plate by [[Eadweard Muybridge]]. The horse's body demonstrates squash and stretch in natural musculature.]]
The principle is based on observation that only [[Stiffness|stiff]] objects remain inert during motion,<ref name="The Illusion of Life"/>{{rp|47}} while objects that are not stiff, although retaining overall volume, tend to change shape in an extent that depends on [[inertia]] and [[elasticity (physics)|elasticity]] of the different parts of the moving object. To illustrate the principle, a half-filled flour sack dropped on the floor, or stretched out by its corners, was shown to be retaining its overall volume as determined by the object's [[Poisson's ratio]].

Examples of the elasticity of the human body in motion were found in photographs the animators found in newspaper sports pages. Using these poses as reference the animators were able to start "observing (the motion) in a new way".<ref name="The Illusion of Life"/>{{rp|48}} Author Walt Stanchfield said: "A simple shape plus squash and stretch are all the anatomy you need for cartoon characters".<ref name="Drawn to Life"/>{{rp|84}}