Slingshots
The basic premise behind all catapult types is turning potential energy into kinetic energy, using it to release an object. A toy for most kids -- and a weapon for some hunters -- exists in a common slingshot, which is also a miniature catapult. Slingshots usually use a stretchable plastic material, which connects to two crossbars. The user places a projectile within the center of the stretchy piece, stretches it, aims and fires.
Aircraft Carriers
An essential use of catapults still comes from the military -- specifically from Navy aircraft carriers. Each aircraft carrier contains four different catapults that are used to get planes up to high speeds to allow them to take off with extremely short runways. The catapult consists of two cylinders that contain pistons.
Clay Shooting
Clay-shooting offers many advantages. It allows hunters to shoot at a target without actually shooting anything that's alive, it provides an opportunity to practice at a rapid pace and it also allows a moving target. Clay shooting is exhibited in many competitions each year. It all stems from a simple catapult that closely resembles an ancient ballista catapult, shooting objects in a straight line into the air, usually at a 45-degree angle.
Other Catapults
Although ancient catapults don't exist today for practical purposes, many workable units still exist for museums or demonstrations. These include trebuchets, which are large launchers that use a heavy counterweight to launch objects; a mangonel, which contains four wheels and launches projectiles with an arc pattern; or a ballista, which shoots objects in a straight line.