Silly / Absurd

#96 · Tiny catapult arm

Tape one end to a cotton reel, load the other end with a pea or mini marshmallow, and launch. Engineering at its finest.

A chopstick, a bottle cap and an elastic band make a desk catapult that will send a cotton wool ball a good 15 to 20cm - which is exactly far enough to be entertaining and not far enough to cause an incident.

How to do it

1. Glue a small bottle cap to one end of the chopstick as the bucket.
2. Tape the chopstick to the edge of a desk about two thirds of the way along, so the cap end overhangs.
3. Load something soft and light into the cap.
4. Press the cap end down and release.

Why it works

The chopstick is a spring. Bending it stores elastic potential energy in the wood, and releasing it converts that into kinetic energy in the projectile. Bamboo is good at this because it bends a long way before it yields - the same property that makes it a traditional bow material.

Tips & warnings

• Cardboard targets and a scoring system turn this from a thirty-second novelty into an actual afternoon.
• Taping further from the cap gives a longer throwing arm and more range.