To study the principle of hovercraft.
The principle that air reduces friction is used in industry. Heavy components are moved on the assembly line by sliding them over a thin film of air.
balloon, plastic tube, plastic bottle cap, CD
Make a small hole in the bottle cap and tightly fit a plastic tube (refill of a pen or body of sketch pen) into it. Fix this cap onto the centre of the CD by using an adhesive. Tie a balloon to the plastic tube. Inflate the balloon by blowing air through the pipe (on CD side). Put the CD over a sheet of glass or similar smooth surface and see how it moves.
The air from the balloon forms an air cushion between the CD and the surface. This reduce friction between them. Air from balloon also exerts pressure on the surface. This makes the disk to float and move. This principle is used in hovercrafts in real life.