To make a Boomerang.
From a piece of heavy cardboard cut a small L-shaped boomerang. The ends of the boomerang should be rounded as shown. Hold it at one end and throw it upwards at an inclination. The boomerang will then whirl forward and up and then glide back toward you along the same path. The spin of the boomerang is essential to its working as it converts the cardboard into a simple gyroscope. As long as the spin continues it will maintain the same plane of rotation. The force of air on the rotating ends and inclined blades pushes the boomerang back.