# How a Trebuchet works MFET 3320 Machine Design Geoff Hale.

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How a Trebuchet works MFET 3320 Machine Design Geoff Hale

Introduction  A trebuchet is a medieval siege engine, a weapon employed either to batter masonry or to throw projectiles over walls. Trebuchets can launch objects from 500 to 1,000 feet.

History  The trebuchet is thought to have been invented in China between the 5th and 3rd centuries BC. The device reached Europe around 500 AD.

How it works A trebuchet is powered by a falling counterweight acting through a beam acting as a lever. The trebuchet is cocked by raising the counterweight. A trigger mechanism holds the counterweight up. When the trigger is released, the counterweight falls and the beam pulls the sling. Soon after, the sling lifts off and whips in an arc upwards. When the projectile moves close to the point where the sling makes about a 45° angle with the horizontal, the free end of the sling slips from the hook, and the missile flies free toward its target.

Step 1 1. The counterweight is upright, locked, and the trebuchet is ready to fire.

Step 2 2. The counterweight is falling and pulling the lever arm and sling upwards.

Step 3 3. The counterweight is falling and pulling the lever arm and sling upwards.

Steps 4 and 5 4-5. The sling makes about a 45° angle with the horizontal, the free end of the sling slips from the hook, and the missile flies free toward its target.

Physics of a Trebuchet To find the range of a Trebuchet consider a projectile fired on a horizontal plane that has a velocity vo at an angle a with respect to the horizontal. It will have a range given by sin 45 * cos 45 = ½, which cancels out the 2. Resulting in the range being equal to the velocity^2 divided by gravity.

Other Physics to consider Torque - During the movement of the trebuchet, it will experience a torque due to the unbalanced weights. The moment of inertia about the axle is simply Conservation of Energy Potential Energy =mgh=1/2mv^2=Kinetic Energy

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