We have been working with projectile throwing catapults. The two catapults we have been working with are the trebuchet and the onager. Although they are different catapults there are lots of things the same and lots of things are different.
The power the trebuchet uses to work is gravity. The weights drop and the arm flies over making the projectile (tennis ball) shoot. And then there's the onager which has a force of twisted rope power to work. When you twist rope up it spins and unties really fast this helps the onager’s power. This power is called torsion power.
Although the trebuchet has a longer arm than the onager the onager fires higher, but the trebuchet fires further. The trebuchet flies further because the trebuchets arm is higher than the onager and the trebuchet is double the size of the onager.