Animating squash and stretch – bouncing ball

December 23, 2009

bouncing ball 01Exaggerated squash and stretch is a great way to add amusement and believability to your animation. I have created a demonstration using a bouncing ball made of very flexible rubber.

This demonstrates Newton’s third law of motion, more commonly called action reaction. For every action in one direction, there is an equal and opposite reaction in the opposite direction; even if the object does not move.

bouncing ball 02In this case the moving ball hits the stationary ground with such force that the top of the ball keeps going downwards when the bottom has stopped. The ball keeps the same volume so the sides move outwards. The amount of squash will depend on the material the ball is made of. The energy of the moving ball is not absorbed by the ground; instead it translates into a reverse thrust and causes the ball to fly upwards. Now the ball becomes long and thin as it stretches up. Near the top of the bounce gravity takes over and starts to pull down on the ball. Making the ball squash a little at the top of its bounce gives the illusion of opposite forces acting on the ball.

bouncing ball 03I created the ball animation in CorelDRAW, which is a vector based drawing program. I made just one drawing and then squashed and stretched the ball with the resizing tools that are part of the program. After each transformation I exported the picture to a jpg file. These picture files were imported into Windows Movie Maker and dragged onto the timeline. The sound track was made with a boing.wav that I found with an Internet search. I dragged two boing sounds onto the timeline and adjusted their position to match with the ball hitting the ground.

Here is the movie that I made. Please let me have your thoughts in a comment to this post.

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