How does air escape from a balloon

Where is the air going?

"Knowledge makes you ah!" has again an amazing attempt for you to recreate. It's about air and where it's going. You win every bet - because the air doesn't do what you think!

You take:

  • two balloons
  • a paper or plastic tube
  • two brackets

The experimental setup is very simple: Blow one balloon full and the other only halfway. Close the balloons with a clip so that no air can escape (but do not knot the balloons!). Now push the balloons right and left onto a paper or plastic tube. The balloons must be firmly attached so that no air can escape from the sides. Once you have assembled the whole thing, think about what will happen when you loosen the clamps and the air can flow freely. Where is she going to do it?

The obvious assumption is: from the bulging balloon to the half-filled one, so that the air distribution is balanced. But not true! If you now loosen the clamps, you will see: The air flows from the half-inflated balloon into the already bulging balloon.

How can that be?

If you inflate a balloon, the first blowers are the heaviest, and this requires the most force. Later it almost works by itself, because the skin of the balloon doesn't stretch that much anymore. Even if it doesn't look like it, the skin of the less inflated balloon was under more tension than that of the fuller one. And consequently - as soon as the air is given the opportunity to escape - the stronger tension ensures that the air flows into the balloon, which is less under tension - i.e. from the emptier to the fuller. Ah!