The Giant Sling: How a Trebuchet Throws Rocks

Imagine a machine as tall as a house, made of wooden beams, that could throw a rock the size of a beach ball over a castle wall! Long ago, people built a machine just like that. It is called a trebuchet, and knights used it to knock down castle walls.

- What a trebuchet is and what it was used for - The three main parts of a trebuchet - Why a heavy weight makes the arm swing so fast - A new word: counterweight

A trebuchet (say it: treh-byoo-shay) is a giant throwing machine that people used almost 1,000 years ago, before guns were invented. Armies used trebuchets to throw heavy stones at castle walls to try to break them down, so soldiers could get inside.

A trebuchet has three main parts. First, a tall wooden frame that holds everything up, like the frame of a swing set. Second, a long arm that swings around, with a sling on one end to hold the rock. Third, a heavy counterweight — a big box full of rocks or sand — hangs on the short end of the arm.

Here is the exciting part. When the heavy counterweight box drops down, it pulls the short end of the arm down fast. That makes the long end of the arm — the end with the rock in the sling — whip up and around super fast, like a playground see-saw with a heavy friend on one side. The rock flies out of the sling and soars through the air toward the castle wall!

Some real trebuchets built long ago were as tall as a three-story building! Their counterweight boxes could weigh as much as a small car. A trebuchet that big could throw a stone weighing almost as much as a bicycle over 300 steps away.