Catapults

Deffinition: an ancient military engine for hurling stones, arrows, etc (Webster Dictionary)

Was first built in Mideval times to help destroy castle walls during seiges. Stones were usually thrown during this time period with this device. The last time catapults were used in a large scale attack was in World War I. They used it in trench warfare to throw grenades across no man's land into enemy trenches. So catapults do not necessarilly have to throw rocks. It is a machine that can be used to throw anything a long distance, mostly for war reasons though.

How It works:

At the end of the arm, which is the throwing piece, there is a heavy wieght. At the front of the machine there is a crank to pull the arm down. When the arm is pulled down and the end is raised, there is a an extreme force on the rope which causes there to be a lot of potential energy. This is because the arm wants to go down, and so the lighter portion of the arm is thrown, and so is anything else on the other end of the arm with a lot of force. That causes the opject being thrown to be thrown a great distance. For the object to be thrown further, there just needs to be more potential force. That means that the arm needs to be cranked harder and further down. All that together makes a great far away seige weapon.