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Kinetic Energy

Objects in motion possesses energy which depends on their speed and mass.

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

First appearing in the 12th century, the counterweight trebuchet has been used for hundreds of years to hurl objects over long distances. Based on the conservation of energy and torque, trebuchets can launch objects weighing over 350 pounds. Today, trebuchets are often used at the annual 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

A trebuchet that is ready to fire [Figure2]

  • Besides the base, the main component of a trebuchet is the long beam that is attached to the central 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 by bringing the longer side of the beam down, at which point the trebuchet 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 becomes potential, leaving zero kinetic energy. When the counter weight is released, it plummets towards 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. Why would the maximum angle for launching projectiles from a trebuchet be 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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