Air cannon

HOW

1. Strike the rubber part of the cannon with your hand.
2. Note the behaviour of objects that are in front of the cannon.
3. To change the direction of the ‘shot’ vertically, press the black button.
4. Stand in front of the cannon and ask someone to ‘fire’ it.

WHY

By hitting the rubber part of the cannon, air is forced out through a hole in the barrel. There are frictional forces at the edge of the hole. They induce rotation of the air layer close to the edge. In this way, they lead to the formation of an aerial ring – a vortex, similar in shape to a smooth bagel. The vortex ring is a very stable formation and moves through space almost like a solid body.

Smoke rings are also sometimes formed by active volcanoes. In contrast, similar rings that form underwater are a common way for dolphins to communicate.