Friction is a force that exists wherever two surfaces are in contact and pressing against each other. Even surfaces that look and feel perfectly smooth are covered in microscopic bumps and valleys — and when one surface slides against another, those microscopic features catch and drag against each other, converting kinetic energy into heat and sound. That is what friction does. That is all friction is.

When you open the valve on the Ghost Glider, air from the balloon escapes downward through the bottle cap and out through the central hole in the CD. That stream of escaping air creates a thin cushion of pressurised air between the bottom of the disc and the surface below it. The pressure of that cushion is just enough to lift the CD a fraction of a millimetre off the surface — not visibly floating, but no longer pressing directly against the table.

Without direct contact between the CD and the table, there is almost no friction. The disc is riding on air, not on the surface. A gentle push sends it gliding with almost nothing to resist its motion. The moment the balloon empties and air stops escaping, the cushion collapses. The CD sinks back onto the surface. Contact — and friction — are immediately restored. The disc stops almost at once.


In precision manufacturing, air bearing tables use thousands of tiny holes to pump air upward, floating large, heavy objects on an air cushion for inspection and assembly — the same physics applied to factory floors worth millions of dollars. For a completely different role for friction — where it actively reverses a direction of travel — see [The Disobedient Hoop]. And in [Newton's Question: Who Moves?], friction against the floor is the only force that can prevent motion on rolling surfaces — which is why a smooth floor is essential for that experiment to work.