|Trebuchet versus Catapult
NASA uses ejection seats when emergencies arise to quickly evacuate the pilot or astronauts from a spacecraft. When an ejection takes place, a catapult fires the seat along a set of rails. A catapult is on aircraft carriers, too. It is like a huge rubber band and is used to propel an aircraft to higher speeds over a short distance in a few seconds.
The catapult evolved during medieval times. Two major developments occurred in the area of siege artillery during the late Middle-Ages. The first, the introduction of the crossbow to England by the Norman invaders, occurred in 1066. The Norman crossbow was cocked by hand or with a winch mechanism and fired from the shoulder; a crossbow loaded with a metal-tipped arrow was capable of piercing even the thickest armor. The crossbow's role in warfare ended in large part at the beginning of the 16th century due to the advent of gunpowder weapons, but still remains in recreational use around the world today.
The second development was the trebuchet in the 12th century. The trebuchet was a giant stone-throwing engine powered by gravity in the place of tension or torsion (catapults). A trebuchet built and currently maintained in England with a 12,000-pound counterpoise attached to it's arm that is capable of throwing a 1,400-pound car 87 yards and a 100--pound iron weight 235 yards. Such engines wrecked havoc around Europe and were employed by the Crusaders during their sieges in the Near East.
The term catapult comes from the Greek word (katapultos), which was the earliest type of ballista. It has developed into a generic term for a variety of missile-throwing engines. There were four basic power sources used for catapults in medieval times: tension compression, torsion, traction, and gravity.
The gravity-powered trebuchet looks has a different power source, relying on the dropping of a large weight, which causes the arm to spring to a vertical position. Generally, they used a single large weight, but a version with weights on either side, called a couillard was also used. These devices were sometimes used for throwing people.
In this lesson, students will research the history and design of catapults and trebuchets.
They will construct and have a mock battle between them.
Discuss with the class that a trebuchet and a catapult is a lever. A lever works by applying force in some way to gain a mechanical advantage. A mechanical advantage is the ratio of the force, which performs useful work of a machine to the force, which is applied to the machine. A lever is characterized by a fulcrum or center of rotation, a force arm, and a weight arm. The force arm is the distance from the fulcrum to the point where force is applied. The weight arm is the distance from the fulcrum to the center of gravity of the weight. A lever has four basic parts: the lever (it’s long and rigid), the fulcrum (resting point where the lever turns or pivots), the effort (the force you apply), and the load (what you want to move).
Discuss with the class how the following factors will affect the accuracy of their devices.
Weight of the object thrown
Strength and length of the arm
Flexibility and speed of the arm
The angle and height of the launch
Have the teams present their design of the catapults or trebuchets.
Ask the class which device was more accurate.
4. Draw one of each of the tree class levers in the space provided. Include the load, effort force and fulcrum.
First class lever: the fulcrum is between the force and the weight.
Second class lever: the weight is between the fulcrum and the force.
Third class lever: the force is located between the fulcrum and the weight.
Where are the fulcrum, force arm, and weight arm located on the trebuchet?
Draw a detailed diagram to place the following into class 1, class 2, or class 3 levers:
Wheelbarrow = __________________
Bottle Opener = __________________
See Saw = __________________
Row Boat = __________________
Draw a detailed diagram to describe where are the lever, load, and effort on the trebuchet?