Activity:

Balloon Air Pressure Magic

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What You Need:

  • Tack or pin
  • 2 clean, dry plastic bottles (1-2 liters)
  • Balloons

What You Do:

  1. Begin the experiment by secretly using the pin or tack to make a small hole in the bottom of one of the plastic bottles. You’ll want it to have a diameter of about ⅛ inch. If your hole is slightly bigger, that’s fine.
  2. Find two volunteers to help with your magic trick, preferably a kid and someone older, such as a teenager or an adult. 
  3. Give the child the bottle with the hole, and give your other volunteer the bottle without the hole.
  4. Instruct your volunteers to place a balloon inside of their plastic bottle, pulling the opening of the balloon back through the bottle opening and securing it over the top of the bottle. The bottle opening should be completely covered by the balloon.
  5. To make this "magical" deception even more fun, invite another volunteer to try to blow up a different balloon. Offer him the bottle with the hole in it, but cover the hole with your finger. Your kid will get a kick out of being the only one to successfully blow up her balloon!

How Does This Work?

Typically, when a balloon is blown up, air is moved into a compressed space to inflate it. However, when the balloon is placed inside of a bottle—and there’s no hole, meaning no place for the bottle’s air to escape—the pressure that occurs from blowing on the balloon isn’t as great as the pressure inside of the bottle. In this instance, the balloon simply won’t blow up. When the compressed air can escape via the hole at the bottom of the bottle, the balloon can expand.

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