During the Middle Ages, Europe saw around 1,000 years of castles and kings. And along with these massive stone structures and ruling monarchs came enormous siege weapons designed to tear them down.

Two types of siege engine commonly associated with medieval warfare are catapults and trebuchets. Many people use these terms interchangeably, but they actually refer to different things. So, what is the difference between a catapult and a trebuchet?

In short, a catapult is a general term for any weapon that launches a projectile. A trebuchet, on the other hand, is a specific type of gravity-powered catapult. So while all trebuchets are catapults, not all catapults are trebuchets.

What is a catapult?

Catapults are siege weapons designed to throw heavy stones and other projectiles. They were reportedly invented around the 5th century BC in several places across the world, including Greece, India, and China. However, catapults were still commonly used even in World War I, where they were used to throw hand grenades across no man’s land!

Catapult design

Throughout their 2,000+ years of use, catapults have had many different designs. But they typically feature a long throwing arm with a bucket on the end that’s drawn back with a restraining rope.

To use a catapult, you wind a winch that pulls the restraining rope back tightly. This lowers the throwing arm so projectiles can be put in the bucket. Once it’s full, you release the restraining rope, allowing the throwing arm to spring forward and launch the projectiles.

Medieval catapults were usually made from wood and reinforced with metal, leather, ropes, and other materials. They also tended to have wheels attached to the frame so they could be easily moved around.

The science behind catapults

Catapults like mangonels, onagers, and ballistae use potential energy in the form of tension (stretching) or torsion (twisting) to pull back a thrower. When this potential energy is released, it’s transferred into the projectile, which causes it to fly.

What is a trebuchet?

Trebuchets are a special type of catapult that uses a lever and gravity to launch a projectile. They consist of a long beam attached to an axle fixed high above the ground. By making one side of the beam longer than the other, trebuchets generate mechanical advantage (the ability to get more force out than you put in).

Trebuchet design

The basic frame of a trebuchet is triangle shaped. At the top point of a triangle is an axle, which acts as a fulcrum (the turning point of a lever) for a long beam. One side of the beam is very long with a sling attached to the tip. The other side is short and carries an extremely heavy counterweight.

To use a trebuchet, you start by raising the counterweight – often using human strength. This lower the long arm to the ground, so you can fit a heavy projectile into the sling. When you drop the counterweight, it causes the long arm to shoot up into the air and throw the projectile toward its target.

Since medieval trebuchets were so large and heavy, they were very difficult to move. So they were usually constructed onsite.

The science behind trebuchets

Imagine you have a lever that’s six feet long with the fulcrum precisely in the middle. When you push down the tip of one side by one foot, the tip of the other side will move up by one foot.

Now move the fulcrum so that one side is five times longer than the other. In this case, when you push the tip of the short side down by one foot, the tip of the long side will move up by five feet!

Dropping the counterweight on the short arm of a trebuchet causes the long arm to move upwards incredibly quickly. When the counterweight hits the ground, the long arm stops moving. But the kinetic energy (the energy of movement) stored in the long arm transfers to the projectile. So the projectile keeps moving and flies out of the sling.

Similarities between catapults and trebuchets

• Both are used to launch projectiles.
• Both rely on stored energy.
• Both use long arms to throw objects.
• Both were used as siege weapons in medieval warfare.

Differences between catapults and trebuchets

• Catapults use tension or torsion to launch projectiles. Trebuchets use a counterweight and lever.
• Catapults store energy in a rope, which moves to the projectile when released. Trebuchets use the force of gravity to move energy from the counterweight to the projectile.
• Catapults are small, light, and easy to move. Trebuchets are large, heavy, and difficult to move.
• Trebuchets throw projectiles much further than catapults. But catapults are usually more accurate.
• Trebuchet projectiles are typically much heavier than catapult projectiles.

Build and test your own catapults and trebuchets!

Learning about the differences between catapults and trebuchets is interesting. But just reading about them is nowhere near as fun as trying them out for yourself!

With our all-inclusive hands-on Discovering Catapults & Trebuchets Multipack, kids get two amazing activity kits that let them build and test their own devices. As well as giving them a medieval history lesson, these kits teach kids about force, accuracy, and precision, and encourage them to conquer real-world engineering challenges.

In addition, we also offer the following related activities:

• Creating Catapults
• Innovating Catapults
• Innovating Trebuchets
• Discovering Torsion Multipack