Compressed air is a powerful force that can be easily harnessed with a balloon to make a working toy car. Using only a piece of cardboard, wheels, a few straws and some glue, an air-powered car is easy to design and fun to race. This simple idea will allow a wide variety of toy car designs, and the finished car will provide your child an opportunity to understand and experiment with the natural power of air.
Design the car on cardboard or foamboard. Draw whatever design you like for the car, but you should make it at least three inches wide and five inches long. If you don't have access to wheels, you can easily make a set out of your leftover cardboard or foamboard; simply trace around a glass to make a smooth wheel, and draw an X in the center. Repeat three more times.
Cut out your balloon car design. Cut the base out, and the four wheels if applicable.
Flip the car base upside down, then tape and glue the straight straws to the base. These straws will hold the toy car's front and rear axles. Place the straws at the front and back of the car, perpendicular to the sides of the car, and parallel to each other. You can trim the straws close to the base of the car if it fits your design better.
Attach a wheel to a skewer or dowel to act as an axle. If you have a cardboard wheel, pierce it at the exact center, in the X mark. Push the axle through one wheel and tape or glue it into place. Do the same with another wheel and the remaining axle.
Push the axles through the two straws, and test that they will spin freely. Glue or tape the remaining wheels on the exposed axle ends, making sure the wheels are fairly close to the edge of the car and that no glue gets into each straw.
Roll the car on the floor a few times to make sure that it will roll smoothly and straight. If not, adjust the wheels or axles accordingly.
Cut a bendy straw to a 4-inch length, with the bendy elbow in the middle.
Stick one end of the bendy straw into the balloon, and wrap the mouth of the balloon with an elastic band to create an airtight seal.
Tape or glue the other end of the bendy straw to the center of the back of the car. Make sure the straw is parallel to the sides of the car and perpendicular to the axles. Let the straw hang off the back end of the car by one-half inch.
Inflate the balloon through the straw, and pinch the end to stop the air coming out. Put the car on the ground and release the straw to send the car rolling.