Lever: A bar that sits on a pivot, like a crowbar or a shovel. Sometimes used to move heavy objects. Catapults are also a kind of lever.
Kinetic energy: Energy of motion. A ball speeding through the air is demonstrating kinetic energy. So are you when you move.
Parabola: A particular curved shape that things launched from a catapult follow.
Potential energy: Stored energy. The ball waiting to be launched has potential energy.
Projectile: An object that is launched through the air.
Tension: A force that pulls on both ends of an object and causes it to stretch.