Do it yourself

Balloon sound

PROJECT COURTESY OF THE EXPLORATORIUM, SAN FRANCISCO

This project is all about the sound of science. Using a balloon and some carbon dioxide, teens can create their own sound-amplifying apparatuses (as if the music they listen to weren’t loud enough). Think of it as an aural magnifying glass. As sound waves enter the balloon, they slow and bend. The balloon focuses the waves to create a loud spot. The project comes from San Francisco’s Exploratorium, where visitors of all ages can immerse themselves in learning about science, art and perception. For a teen twist on the experiment, try amplifying a cellphone or some favorite tunes. Who knew that learning about the properties of gases could sound this good?

Materials

Sturdy balloon (12-16 inches in diameter), a way to fill the balloon with carbon dioxide (CO2) just before use, such as crushed dry ice (available at many supermarkets and fishing/bait shops), thick leather gloves (if using dry ice), tongs (if using dry ice), a flask or 1- or 2-liter plastic soda bottle.

Optional: toy metal clicker or other noisemaker such as a cellphone.

Process

Inflate the balloon with carbon dioxide gas. If using dry ice, put ¼ cup into the bottle. Fit the balloon over the top of the bottle. The balloon will slowly fill as the dry ice warms (10-15 minutes). When the balloon is full, remove, and tie it off Have one person hold the balloon up to her ear and another experiment with the level and position of sound on the other side.