How Do Catapults Work?

By: Yara Simón  | 
A young man fires a stone from a slingshot.
A catapult hurls an object through the air. Jason Edwards / Getty Images

Catapults have played a fascinating and pivotal role in the history of warfare and engineering. Throughout history, they underwent technological advancements and became bigger and more powerful.

It's difficult to pinpoint where they originated, but different groups — such as Roman, Arab, Chinese, and Greek armies — contributed to the design. They used these machines to launch various projectiles with incredible force and accuracy.


Read on to learn more about early catapults, the mechanics of these machines and how you can build your own catapult with a few everyday objects.

What Is a Catapult?

Though the definitions for types of catapults vary, each share one goal: to hurl an object through the air. The word "catapult" comes from the Latin word catapulta and the Greek word katapaltēs, meaning "to hurl."

Here are a few types of catapults:


  1. Torsion catapult (ballista): The ballista looked like a giant crossbow (see this page for a picture) and had a relatively compact design with a wooden frame and two arms. Twisted ropes provided tension to power the launch.
  2. Counterweight Catapult (trebuchet): The trebuchet is perhaps one of the most iconic types of catapults. It featured a large wooden frame with a long throwing arm and a counterweight at the opposite end. You would load a projectile into a sling attached to the throwing arm. When you release the counterweight, it fell, causing the throwing arm to swing upward, launching the projectile in a high arc. Trebuchets had a distinctive appearance with their tall frame and long arm.
  3. Aircraft catapult: In modern naval aviation, aircraft carriers use catapults to launch fighter jets. These catapults are highly advanced and are typically steam or electromagnetic (EMALS) catapults. They have a linear track along the flight deck and use a shuttle or launch bar to propel the aircraft forward at high speed over a short distance.

Catapults can throw objects a fair distance — 500 to 1,000 feet (150 to 300 meters) is 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 put a great deal of energy into the catapult over a period of time. Then all of the energy releases at once, throwing the projectile.


Early Catapults

Catapults have existed for millennia, with their origins dating back to ancient times. As William Gurstelle writes in "The Art of Catapult: Build Greek Ballistae, Roman Onagers, English Trebuchets, More Ancient Artillery": "Before the days of gunpowder and iron or steel cannon barrels, siege engines (catapults) were the artillery of the ancient armies."

The ancient Greeks and Romans were among the early civilizations to employ these formidable weapons, with Greek writers and historians documenting them in their works. But there are also records of catapults in other parts of the world, including China, the Middle East and India.


The Greeks' catapults were heavy and took time to load. "In general, these early catapults obtained their shooting power from bending back a wooden or animal-horn bow or leaf spring," Gurstelle writes. By the third century BCE, Greeks began to use a coiled rope to create a spring.

During the Middle Ages, catapults underwent significant advancements. They became larger and more powerful, capable of launching stones, arrows and other projectiles over great distances. The development of twisted rope and the use of tension played a crucial role in enhancing their effectiveness.


The Mechanics of a Catapult

A typical catapult consists of several key components, each contributing to its functionality:

  1. Catapult arm: The catapult arm is the long wooden beam or lever that holds the projectile. It is the part that moves when the catapult is fired.
  2. Tension: Tension, often created by twisted rope or other means, stores the energy required to launch the projectile.
  3. Sudden release: When the tension is suddenly released, it transfers the stored energy to the catapult arm, causing it to swing rapidly and launch the projectile.
  4. Counterweight (in some designs): Some catapults, like trebuchets, use a counterweight to generate force. The counterweight is raised and then dropped, creating the energy needed for the launch.
  5. Wheels (in some designs): Some larger catapults are mounted on wheels to facilitate movement and positioning.


Build Your Own Catapult

For those interested in the mechanics of catapults and the principles of force and tension, you can build your own version. You can craft a simple catapult using everyday materials like wood craft sticks, a rubber band and hot glue. Learn how to make one here.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.