Balloon in a Bottle

Concepts – air pressure, compressibility of air, particulate nature of matter

Materials – 1-liter bottle, latex balloon (9” works well), push pin or tack

Procedure – Without letting go of the balloon, place it in the 1-liter bottle and wrap the balloon around the mouth of the bottle. Once the nozzle of the balloon is securely wrapped around the mouth of the bottle let it go. Now try to blowing up the balloon inside of a one liter bottle. Good luck with this.
Next, poke a hole in the bottom of the bottle using a tack or pushpin. Before pulling the pushpin out of the bottle widen the hole it has created by rotating it in a circular motion. Remove the pushpin and try blowing up the balloon again.
While the balloon is still inflated, cover the hole in the bottom of the bottle with a finger and take your mouth off of the balloon. It should remain inflated. Then take your finger off of the hole in the bottle and watch the balloon. It should deflate.

Explanation – Initially the balloon inflates very little because the bottle is already filled with air and there is no room for the balloon to expand. When a hole is punched in the bottle the air molecules in the bottle have an exit and are pushed out as the balloon fills the space. If you plug the hole with your finger the balloon stays inflated. When you take your finger off the hole outside air flows back into the bottle as the balloon collapses. The elasticity of the rubber in the balloon shrinks it to its original size as the air rushes out the top of the bottle.

figure25.jpg
Figure 25: Balloon in a one-liter bottle.

*Adapted from “Balloon in a Bottle”, Investigating Solids, Liquids and Gases with TOYS and “Water Balloon in a Bottle”, SteveSpanglerScience.com

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