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Try this very simple project to create a floating disc that skims across a surface similar to the way an air hockey puck or hovercraft does.
A hovercraft works by forcing air out beneath it, creating a cushion of air to float on. Hovercrafts usually have a "skirt" that surrounds the base to contain the air; in this project the CD is light enough that it doesn't need a large cushion, so no skirt is necessary. The balloon acts as a pressurized gas chamber. When you open the cap, the balloon forces air out through the cap, creating a thin cushion of air beneath the CD.
As you nudged your hovercraft around, you may have noticed that it zipped along the surface like an air hockey puck. That's because air hockey uses the same principle, with the puck floating on a layer of air. In the case of an air hockey table, the air is forced out from the table below rather than a source above like a hovercraft. Try pushing a plain CD across the table, and then your hovercraft. Do the two move differently? That's because the thin cushion of air from the hovercraft reduces the friction between the CD and the table. Because of the reduced friction, hovercrafts can reach higher speeds.