Click to drop a ball, or grab one and throw it. The graph follows the last ball you touched. The address of the page keeps the settings, to share them.
Each bounce a little lower
When a ball hits the floor, it comes back up slower than it came down. The ratio of the two speeds is its bounciness (physicists call it the coefficient of restitution, e): about 0.9 for a super ball, 0.75 for a basketball or a tennis ball, almost nothing for a ball of clay. The height a ball reaches grows with the square of its speed, so each bounce rises to e² of the one before: a basketball keeps about 60% of its height every time. The graph under the room measures it.
The bounces also get shorter, by e each time. In theory a ball bounces forever, but all those bounces add up to a finite time, like Zeno's arrow that never reaches its target but does: dropped from 2 meters, a basketball should be done in about 5 seconds. In practice, the last tiny hops are lost in the vibrations of the floor, and the ball rolls.
Air matters too. Its drag grows with the square of the speed and weighs most on light balls: a ping-pong ball falls a lot slower than a golf ball of the same size, and hardly slows a bowling ball. Change the gravity to see the same ball float on the Moon or slam down on Jupiter.
Squash and stretch is not physics but the first of the twelve principles of animation from the Disney studio: a ball that flattens when it lands and stretches when it falls fast feels heavier and livelier than a perfect circle. Turn it off to compare. For the same bounce in a few lines of CSS, with no JavaScript, see the CSS bouncing ball.