Build a Balloon-Powered Car

What You Need:

  • Clean, dry, half-gallon milk carton with the top cut off, cut in half along the length of the carton
  • 4 spools (or substitute your own items for wheels, such as large bottle caps)
  • Straws
  • Balloon (and some extra ones, too!)
  • Hot glue gun and glue

What You Do:

  1. For starters, you may want to decorate the milk carton. While this won't make the car go faster, it will make the ride more swank! You can use tempera paint to cover the outside surface (put in a drop of dish soap so that the paint will stick to the waxy coating of the milk carton), or glue on strips of colored paper, and draw on windows and doors with a marker. Beware: don't cut holes in the milk carton. The only holes will be those you make for your balloon and the axles.
  2. Cut a hole in the middle of the back side of the carton for the balloon. Start with a small hole; you may need to make it bigger later if it doesn’t let enough air escape from the balloon.
  3. Put the open end of the balloon through the hole.
  4. Next, make some holes in the sides of the carton for the straws to form axles (the straight stick-like parts of the car that hold the wheels). These holes need to be close to the bottom of the carton.
  5. Stick the straws through the holes and glue on the spools to form wheels.
  6. Now the car is built and ready for testing. Before you try it out, be sure to explain the principle behind it. Have your child fully inflate a new balloon, hold onto the end without tying it, and then let it go. What happens? It should zip around the room until the balloon is fully deflated. When the air comes out, it pushes the balloon with equal force in the opposite direction. The gas powers the movement of the balloon. The same principle works for the car as well.
  7. Ask your child to predict what is going to happen when he inflates the balloon in the car, and lets it go.
  8. Now, try it out! Inflate the balloon, but don’t tie it closed. Let go. What happened?

Note: You may need to make some adjustments to tweak the design of the car, the size of the hole holding the balloon, or the size of the balloon. It’s all about problem-solving. Encourage your child to keep trying until it works—just like all the great inventors of the world!

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