Squash and Stretch are the first two principles of Animation. These first two principles are to produce an illusion of objects or characters moving with the laws of physics at work. Many see these first two principles as being the most important. Squash and Stretch show the physical properties of a body or object have gravity and weight.
Applications of stretch and squash can vary. For instance when taken to an extreme a figure stretched or squashed can have a comical effect or an object that has an exaggerated stretch or squash may be made from an extremely malleable substance.
Exercise: Applying Squash and Stretch to a Simple Ball Animation
Things to remember: When the ball touches ground it squashes. Squash and Stretch reflects the density and velocity of an object. A baseball is more dense and therefore would have less squash than a water balloon.
Important: Object can not lose its volume. Therefore make sure that as your object stretches it becomes longer or as an object squashes it becomes flatter.