This exercise is taught as the first assignment in the Animation Workshop at UCLA, using pencil and paper. I wanted to see how easy it would be to create it using the Flash animation program.
After drawing a ball "symbol" and creating 30 blank frames, I drew a motion path for the ball to follow. The goal is a symetrical path so that when it loops it will look more continuous.
Next I took the ball and keyframed it at five frames (left to right): numbers 1, 8, 15, 23, and 30. These represent the extremes of the motion.
Then I used the Scale Tool to squash the ball at the second and fourth keyframes. (I was getting ahead of myself, as you will see.) This is to create the effect of the ball hitting a surface as it bounces. Without this squash effect, the ball would appear to be made of steel or marble.
Then I put Interpolation at the first four keyframes, using Ease In at the first and third, and Ease Out at the second and fourth. This causes the ball to speed up as it falls and slow down as it rises. However, the ball begins to squash before it hits the surface, which would not happen, and gives an undesirable floating effect.
So then I went back and removed the squash from the second and fourth keyframes, which gave me the inbetweens as per a steel ball. This was in order to create undistorted images of the ball throughout the sequence.
Then I froze the frames just before the second and fourth keyframes by making them into keyframes themselves. I then re-squashed the "hit" keyframes and now only the frames following those are affected, with the frames before the "hits" remaining undistorted.
Next I took the frames right after the "hit" keyframes and made them into keyframes, and used the Rotate Tool to align the stretch along the motion path. This creates a smoother action and accentuates the bounce further.
Seems easy with hindsight. The best part was that I could view the animation immediately as I was working on it, without having to record it on video or film first.