Put a ball drawing near the top of the screen and another drawing much lower where it meets the ground. You already have two drawings of a bounce. The upper drawing is the peak of the bounce. The bottom drawing is the contact frame. Keep your ball drawings simple and don’t worry about adding shadows, background, or details. The goal of the exercise is to focus on motion and not creating a full scene.
Add some in-between drawings between the top drawing and the ground. Don’t spread them equally. Place the ball positions closer together at the top of the bounce since the motion is slowing down. Move the ball positions further apart as the ball falls so that it’s accelerating. The ball should seem to spend more time around the top of the arc and move faster as it nears the ground.
The contact frame also lets you play with shape as well as timing. A cartoon ball can squash slightly as it hits the ground, getting a bit wider and flatter for a frame before returning to its original shape. Be careful not to overdo it with the squash. If the volume of the ball seems to double or vanish entirely, check the dimensions of adjacent frames and adjust the proportions.
Next, work on the upward part of the bounce. Once the ball leaves the ground, you need to move away from the ground quickly, so the first few positions can be spaced further apart. As the ball rises, decrease the spacing once again so it gets closer together as it nears the top of the arc. This will ease out of the contact and ease into the top of the arc. You can make the second bounce lower than the first if you want the bounce to seem like it’s losing energy.
One common problem when working on this exercise is focusing too much on the drawings and not enough on the motion arc. Place a dot on the center of the ball in each frame and visualize a smooth line that connects those dots. If one drawing is off to the side too much, the playback may show a weird wobble even though the individual frames look correct. Onion skin is helpful for seeing the neighboring frames, but it’s still important to view the animation at full speed to see the overall effect.
When you feel you’ve got a good bounce, change just one thing and see how it affects the animation. Add an extra frame at the top, make the fall faster, remove some of the squash, or change the height of the second bounce. Making small changes will help you understand how timing, spacing, shape, and arcs work together. When the animation looks great, instead of looking at the final drawings, notice how far apart the ball drawings are placed; these spaces are responsible for most of the illusion of weight and speed.
