Trebuchet

Challenge: To design a trebuchet that will launch a projectile over a barrier towards a target.

Parameters: The trebuchet must fit in a locker and be no more than 30 cm tall before being triggered. It can only use up to 500 g of mass for the counterweight. The projectile must be a ball of plasticine or similar substance. It must clear an obstacle (castle wall) 1.52 m tall. Goggles must be worn at all times. You may not keep your project in the classroom between classes.

Scoring: Your trebuchet will be scored on several parameters, some of which you want to maximize, and others you want to minimize:

Mass of projectile (m) in grams

Mass of Trebuchet (M) in kilograms

Distance past the obstacle (d) in meters

Symmetry of the parabola (S) as a ratio greater than one, of distance of trebuchet from wall and distance projectile first lands from the wall on the other side.

Formula: m d / M S

Rank will be based on score, with highest score earning highest rank.

Physics: The path of a dense projectile upon release is approximately a parabola. The initial velocity and launch angle are mathematically related to the maximum height and horizontal displacement. In fact, every aspect of the motion can be calculated at the grade 12 level. This is because we can assume the horizontal motion exhibits constant velocity while the vertical motion exhibits constant acceleration due to gravity, and that those two components are independent of each other.

Extensions: Getting the best result will involve achieving a large initial velocity with a large projectile. That means a lot of Kinetic Energy. To do this requires an efficient conversion of Gravitational Potential Energy stored in the raised counterweight, through levers and fulcrums, to the end of your trebuchet arm.

Help/Hints: Maximizing lever length within the size limit requires creativity. The trebuchet can exceed the size limit after being triggered. A swinging fulcrum or cam-style fulcrum is efficient but difficult to make. All moving parts should be as light as possible so that less energy is wasted as kinetic energy of your trebuchet. All sources of friction should be minimized to improve efficiency.