Friction is the force that slows things down when surfaces rub together. You glue a thread spool over a hole in cardboard. A balloon pushes air through the spool. That air lifts the cardboard off the table so the surfaces no longer rub.

A piece of cardboard floating on a thin layer of air glides across a table with almost no friction. To build one, you cut a small square of cardboard and glue a thread spool over a hole in the center. A balloon fits over the top of the spool. When the balloon releases air, it flows through the spool and lifts the cardboard off the table. Give it a gentle push and it slides surprisingly far. The air layer removes the friction that would normally slow it down.