Balloons are inexpensive items that can be used to teach the principles of propulsion. Using basic items such as toy wheels, cardboard tubes, straws, strings, cardboard, tape and glue, kids can assemble vehicles that are powered by a balloon. Vehicles that can be made include a car, a boat, a helicopter and a rocket.
The balloon-powered car is the most common project for this type of demonstration. In the past, NASA has even sponsored a contest to build the best one. Students can design many different types of balloon cars, though several basic elements are needed. A set of four wheels and a bottom frame is needed on the bottom. Wheels can be bought online or at a local hobby shop, while the bottom frame can be made from a flat piece of cardboard or the lower part of a box or carton. The other key element is a plate on the back of the vehicle with a hole in it to which the balloon can attach. Once the back plate is secured, inflate the balloon and attach it to the hole and let go of the end. Students can customize their vehicles with decorations or aerodynamic attachments.
Balloon boats can be made with a pre-designed kit, available online and at local toy stores, or it can be constructed from household items. To build one from scratch, use a box or a plastic container and poke a hole on one of the short sides. Cut a drinking straw in half and stick it into the mouth of a balloon. Stick the end of the balloon into the hole so the inflatable balloon rests in the boat itself, then secure it to the hole with tape or glue. Inflate the balloon, pinch it closed, set it in water and release.
Balloon helicopters are available as a kit that can be purchased online or at a local hobby store. It includes a set of rotary blades that attach to a base. This base is inserted into the mouth of the balloon, and it has places where three blades can attach to it. When you inflate the balloon and hold it with the mouth facing up, releasing it causes air to push the blades in a circle, creating lift. Some bases also include a whistling mechanism for added effect.
A balloon rocket can be constructed with a long piece of string, a drinking straw, tape and a long balloon. First, thread the string through the drinking straw and run the string across the room. Tape a balloon to the drinking straw so it rests with its open end facing backwards. Inflate the balloon, pinch off the end and bring it to one end of your string. Then release the end of the balloon, and the air inside will propel it along the string, across the room.