The Moving Balloon

I don’t like balloons very much. Whenever they pop, they startle me. This balloon experiment, however, has no popping balloons! Even better, the balloon moves all on its own, so you don’t have to be near it if it pops! This is a super fun experiment, and it is so simple.

What you need:

• A glass bottle with a long neck
• A balloon
• 2 tbs water
• Funnel

Steps:

• Using the funnel, fill your glass bottle with the water.

• Put the bottle in the microwave for 1 minute, or until the water is boiling.
• Take the bottle out of the microwave (be careful, it is very hot!) and quickly attach the balloon around the rim of the bottle.
• Watch as the balloon slowly creeps into the bottle (you will have to be patient, it may take a couple of minutes).

What makes the balloon move?

Water inside the bottle changes state and into water vapor when it is boiled. This water vapor pushes air out of the bottle. When the water cools, the water vapor condenses and turns back into liquid water, creating a difference in pressure between the inside and the outside of the glass bottle. Since the pressure is higher outside the bottle, air rushes into the bottle, taking the balloon along with it. The more the bottle cools down, the more air comes in from the outside, and the more the balloon expands inside the bottle.