Question

How does the ancient catapult work? Twisted rope and wooden gears or levers just don't seem to be able to get the speed up to launch some very heavy loads for a great distance.

Answer

There are several different technologies that fall into the "catapult" catgory. They include the catapult, the ballista and the trebuchet. The catapult is the winched-down bucket that people normally think about when they hear the word "catapult" (see this page for a picture). A ballista is a very large cross bow (see this page for a picture). A trebuchet is a weighted beam that swings a sling carrying the projectile.

Both catapults and ballistas work either by storing tension in twisted ropes, or by storing tension in a flexed piece of wood (in the same way an archery bow does, but on a larger scale). A trebuchet tends to be easier to build because it consists simply of a pivoting beam and a counterweight that rotates it through an arc.

Catapults can lauch things a fair distance - 500 to 1000 feet being common. It is surprising how much energy they can store. The gears are important, because they create a winch. The winch allows a person to store a great deal of energy into the catapult over a period of time. Then all of the energy releases at once, throwing the projectile.

Here are some interesting links to learn more:

• A brief summary of catapult terminology
• The Four Stage of Design for the Torsion Catapult
• Collection of catapults
• Physics of the trebuchet
• Trebuchet plans
• Catapults
• Medieval Warfare links
• Middelaldercentret - Centre for Historical Technology, Denmark

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