Newton's g-Ball

A specially designed ball with a built-in digital stopwatch that times its own fall, from the moment it is released until it lands. The display is easy to read and resolves times from 0.01 to 29.99 seconds, and it resets by holding the button down; the electronics are well protected, though the ball should land on a soft surface such as a mat, cushion or lawn to ensure a long life. The maximum drop height is about 12 m, and air resistance affects the fall by roughly 5%, which pupils can allow for. It makes free-fall and constant-acceleration experiments easy — determining g over a known height, or estimating a building's height from the fall time — and gives hands-on experience of acceleration and gravity.