Science project

Air Pressure Science Experiment: Balloon and a Jar

Research Questions:

When you first set the water balloon on top of the jar, the air pressure outside the jar and the air pressure inside the jar are the same. As the fire burns, air, heated by the fire. rises and pushes its way out of the jar. This hot air pushing out past the balloon causes the balloon to wiggle. However, while hot air is going out, no new air is coming in (the balloon works like a one-way valve, letting air out but not in). So now there is less air, less stuff, in the jar. With less stuff taking up space in the jar, the pressure inside the jar is less than it used to be, that is, less than the air pressure outside the jar. Since the pressure outside the jar is now greater than the pressure inside the jar, what will happen to the balloon?


  • One large glass jar (a big maraschino cherry jar from a bar works well)
  • One balloon
  • Water
  • A bit of paper
  • Matches

Experimental Procedure:

  1. Fill the balloon with water until it’s a little too big to fit through the mouth of the jar.
  2. Light a bit of paper on fire and drop it into the jar.
  3. Quickly place the balloon on top of the jar.
  4. Observe carefully.

 Terms & Concepts: Air Pressure

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