The catapult is basically a type of simple lever or first class lever, which is a device used to transmit force and displacement to an object, by means of the amplification of the applied mechanical force, thus increasing its speed or distance traveled.
These simple levers are composed of a rigid bar that can rotate freely around a point of support (the fulcrum). However what differentiates them from the other levers is that the fulcrum is between the point where the effort must be applied and the point where the resistance is.
With this configuration it is posssible to make several arrangements, depending on the purpose to be achieved, either control and decrease the speed and distance traveled by the object or increase it.