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Conservation of Energy

The amount of energy in a closed system never changes.

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Credit: Paulo Ordoveza
Source: http://www.flickr.com/photos/brownpau/3524417579/
License: CC BY-NC 3.0

Created during the 12th century, the counterweight trebuchet has been used for hundreds of years to hurl objects long distance. Based on the conservation of energy and torque, trebuchets have launched objects weighing over 350 lbs. Today, trebuchets have become popular once again due to their use at the yearly pumpkin chunking contests in Delaware.

Amazing But True

Credit: Tony Crider
Source: http://www.flickr.com/photos/acrider/1812427021/sizes/z/
License: CC BY-NC 3.0

One of the main components of a trebuchet is the long beam that is attached to an axle [Figure2]

  • Besides the base, the main component of a trebuchet is the long beam that is attached to an axle. The long end of the beam houses the projectile while the short end of the beam is where the counter weight is attached. The counter weight is raised up by pulling the longer side of the beam down, at which point the system is ready to be fired.
  • The trebuchet works on the principle of conservation of energy. As the counterweight is raised, potential energy is being stored in the system. Once the counterweight is raised to the desired height, all the energy in the system is potential while the kinetic energy is 0. When the counter weight is released, it plummets to the ground causing the projectile on the other end to rotate. As the counterweight falls, all the potential energy is transferred into kinetic energy (to be more specific, rotational kinetic energy).

Show What You Know

Using the information provided above, answer the following questions.

  1. Where does the potential energy in the system originate from?
  2. Would the maximum angle for launching projectiles from a trebuchet be at 45°?
  3. If the recommended counterweight mass is 100 times the weight of the object to be thrown, how heavy of a counterweight do you need to launch a 100 lb. stone the optimal distance?

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Image Attributions

  1. [1]^ Credit: Paulo Ordoveza; Source: http://www.flickr.com/photos/brownpau/3524417579/; License: CC BY-NC 3.0
  2. [2]^ Credit: Tony Crider; Source: http://www.flickr.com/photos/acrider/1812427021/sizes/z/; License: CC BY-NC 3.0

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