How to Build a Balloon-Powered Car

Learn how to build a speedy car powered by air using simple household materials. HowTo: Family Edition: family how-tos that actually help.

1. Prepare the body. Take your rectangular piece of cardboard. This is the body of your car. If it is too long, trim it to your desired size.
2. Attach the axles. Cut two straws so they are the width of your cardboard body. Tape them firmly across the bottom of the cardboard—one near the front and one near the back.
3. Make the wheels. Ask a grown-up to poke a hole in the center of each of the four bottle caps. Slide a wooden skewer through one straw, then attach a bottle cap to each end of the skewer.
4. Build the engine. Slide the neck of your balloon over a straw and tape it tightly so no air can escape anywhere except through the straw. Tape this straw assembly onto the top of your car body.
5. Launch your car. Blow through the straw to inflate the balloon. Pinch the end of the straw to keep the air in, set your car on a flat floor, and let go!