Try This at Home:
Build a Balloon Hovercraft
What you’ll need:
- Blank CD or CD or DVD you don’t need anymore
- Pop-top lid from a drinking water bottle or dish soap bottle
- 9” Balloon
- Craft glue or super glue
- Masking tape (optional)
Here’s what to do:
- Carefully glue the pop-top lid onto the CD so that it covers the hole in the center of the CD. Let the glue dry. If the craft glue doesn’t hold well, ask an adult to help super glue the lid to the CD. Make sure the hole is completely covered and sealed by the cap. You can add some masking tape around the edge of the cap where it meets the CD to enhance the seal.
- Close the pop-top lid. Blow up your balloon as large as you safely can without popping it and twist (but do not tie) the bottom to hold the air inside. Carefully stretch the opening of the balloon over the top of the pop-top lid. This is easier with two people.
- Let the balloon go and adjust it so that it stands up straight and centered above the lid.
- Now you’re ready to launch! Set your hovercraft on a hard, smooth surface like a table. Gently nudge your CD. How far does it move? Now open the pop-top lid without pulling the balloon off and let the CD go. Watch what happens. How far and fast does your hovercraft move now?
Take it further:
- Try only opening the pop-top lid halfway. How does this affect the amount of time your hovercraft hovers and how far it goes?
- To make your hovercraft last longer, cover the hole on the underside of the CD with a few layers of tape. Then carefully poke five or six holes into the tape. Try using your hovercraft again. Does it hover longer?
- Try blowing your balloon up only halfway. How does the size of the balloon and the amount of air you start with affect your hovercraft?
- Hovercrafts work best on smooth surfaces. What happens if you try to use your hovercraft on carpet or grass?
What’s going on?
When you pushed your hovercraft with the pop-top lid closed, you should have noticed it didn’t go very far or very fast. This is due to friction! Friction is the force that opposes the direction of motion when two surfaces or objects move over each other. The friction between your CD and the table when the pop-top lid is closed is strong enough to stop the CD after only a short distance. When the lid is opened, the air from your balloon flows down through the lid and under the CD creating a thin cushion of air that lifts the hovercraft off the table. Being off of the table reduces the friction between the CD and the table because they no longer touch; they each only touch air. This reduced friction allows the hovercraft to travel much faster and further. The CD needs to be flat so the air can escape underneath it in all directions to create the air cushion that makes the CD hover.