Pratt Institute
Department of Digital Art
Instructor: Claudia Herbst
Course: DDA 310, 3D Computer Animation


Assignment I

Animating a Bouncing Ball


Image by Steve Malaska


Summary: Just about every animation class starts out with a bouncing ball assignment because
what you will learn in convincingly animating a simple ball squashing and stretching as it bounces
applies to almost all types of animation. It is true, if you can convincingly animate a ball bouncing,
you can learn to animate just about everything! The principles conveyed in this assignment are as
simple as they are challenging.

Requirements: Create a ten-second animation (300 frames) of one or two balls bouncing. Focus on
convincingly squashing and stretching the ball(s) as they hit the ground and bounce off. The ball(s)
should hit the ground at least three times and steadily and noticeably lose momentum until coming to
a nice and subtle standstill. For this assignment, camera cuts are allowed, animated cameras are not.


A Few Notes on Squash & Stretch According to the Folks at Disney:

Squash and stretch convey the illusion of weight and volume to a character or object as it moves.

Hardly any action will happen without squash and stretch. If you can believably animate a ball bouncing
depicting squash and stretch you can successfully animate most other objects.

Sometimes squash and stretch will be quite obvious, other times it will be subtle.

Subtlety will result in a more smooth and gentle motion. If you want something more exaggerated,
exaggerate squash and stretch- be careful not to make it look like liquid rubber if that is not what you
are interested in – maybe the objects are very bouncy/responsive but not very stretchable...
Think about the material you are trying to convey- think weight!

Squash and stretch are also important in facial animation. For instance, the eyes, opening wide for
surprise or fear, (stretch), partly closed from the cheek action during a smile (slight squash) or squeezed
into slits from anger or suspicion, or strain, (squash).

A Note on the Ball's Volume:

Be aware that when you are scaling the ball along the Y axis, you are actually subtracting volume from
its shape. In order to compensate, increase X and Z scale values of the ball by the amount subtracted
in Y.



Making the Ball "Snap":

What's wrong with the picture above? This version of the bouncing ball doesn’t show
good contact with only one pose on the ground. Avoid positioning # 5 and #7 at the
same level. This can isolate 6 and cause a visual strobe effect.




Here there's no snap: Pose 7 has NO SNAP because the ball is still on the ground.




Snap - the lucky winner! Poses #5 and #6 show the compression of the ball. Pose #7 has
snap and the ball actually appears to be bouncing!


It may be helpful to draw a curve as a visual aid describing the path your ball will travel.
This curve (or path) can later be deleted. The first arch should be the highest, followed
by two or three shorter ones.