Join George Maestri for an in-depth discussion in this video Squash and stretch, part of Animation Foundations: Fundamentals.
Many things in nature are not rigid and have some degree of flexibility. This means that not all parts of an object will move at once. Take for example a simple balloon. When the balloon hits the wall, the front part of it stops, but the back end keeps going and runs into the mass in front of it, causing the object to squash. Stretch is simply the opposite of squash. If we pull the object, the front moves first and the rest follows along later.
This is very similar to overlap and follow through, but within the object itself. Squash and stretch can be used to add life to animation. When a flexible object changes direction, accelerates or deccelerates, the mass of the object will respond first at the point where the force is applied. The rest of the mass will follow later. When animating squash and stretch in a computer, there are many ways to get this effect. The simplest way is to simply scale the object.
When an object squashes, you scale it down along the direction of the force. Then scale up the rest of the object along the other axis. The opposite is true for stretch. Scale up in line with the force and down along the other dimensions. Many packages have other tools to manipulate the volume of an object and can be used in squash and stretch. There may be squash and stretch modifiers or effects, lattice deformations can be used.
Skeletons and bone systems can also be used. Now regardless of how you squash and stretch objects, be sure to maintain the volume of the objects. If the volume of the object changes, that object will appear to shrink and grow. Remember we are simply rearranging the matter within the object. We are not adding or subtracting mass. So squash and stretch can be used to simulate the way a flexible object respond to force. And however you squash and stretch an object, be sure to maintain that object's volume throughout the motion.
- Understanding forces and motion
- Working with center of mass
- Adjusting frame rates
- Understanding keys and keyframes
- Building animation paths
- Navigating the object hierarchy
- Staging an animation
- Animating to audio and music