The balloon rocket

The balloon races against the direction in which the air flowing out is moving.

The string is stretched horizontally or vertically across the room. The straw is threaded onto it. The balloon must then be inflated and attached to the straw at its thickest point with an adhesive strip. Once everything is attached, let the air out of the balloon.

• 1 string,
• 1 straw,
• 1 balloon,
• 1 adhesive strip,

The string along which the balloon rocket is to race should be as taut as possible.

What is technically behind the experiment

The principle of recoil can be clearly seen in this experiment. According to the law of momentum, the sum of all momentums (mass times velocity) in a system remains constant over time as long as no external forces are exerted on the system. In this case, the system consists of the balloon and the air in the balloon. At the beginning, the total momentum is zero: everything is at rest. When the air flows out, it carries momentum in the outflow direction. In order for the total momentum of the system to remain zero, the balloon must experience an equally large momentum in the other direction. Because the balloon is very light, it moves very quickly.

What this experiment has to do with everyday life

The principle of recoil can also be found in nature, for example in a jet airplane or in an octopus, which can move, i.e. swim, using the principle of recoil.

Verena Bock