How Can a Trebuchet Use Gravity to Launch Objects?

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What is a trebuchet? How can a trebuchet use gravity? What does gravity have to do with launching an object? To begin, a trebuchet is a medieval catapult used for hurling heavy stones. The trebuchet is thought to have been invented by the Chinese and made it’s way to Europe by AD 500. It was used by armies to throw stones to break down barriers like castle walls. Sometimes, bodies of people and animals, that had died from disease like the Black Plague, were even thrown over the walls to try to infect people.

The stones (and bodies) were thrown by the trebuchet using gravity. Gravity is defined as the force of attraction by which terrestrial bodies tend to fall toward the center of the earth. In other words, gravity is what keeps people and objects on the ground! So, if gravity keeps things on the ground, how did people use a trebuchet to throw things? The answer is very simple--they used a “counter-weight.”

To understand what a counter-weight is, think of two kids on a see-saw. One is in the eighth grade and the other is in kindergarten. The eighth grader is going to be a lot bigger than the kindergartener. So when the eighth grader sits down, what’s going to happen to the kindergartener? You guessed it! That little kid is going to go sailing through the air! The eighth grader was bigger and heavier than the other kid and the force of his weight caused an action, in this case his end of the see-saw came down quickly, that created an equal and opposite reaction, the little kid’s end came up quickly. But that’s not the end of it! The speed created, combined with the force, caused the little kid to be thrown through the air. The eighth grader was the counter-weight!

For this project, a simple trebuchet was constructed of wood, with a cloth sling, and counter-weights in the forms of lead weights and a brick. The projectile was a golf ball. The trebuchet was secured by a pin, the “bucket” was loaded with counter-weights, and the golf...
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