Trebuchet Physics

University of British Columbia

Physics 420 --- 2016/2017

Tao Zheng


Visit my actual website here: Trebuchet Physics.


Learning Goals

1) Build up a theory from previous physics knowledge
2) Learn a bit about trebuchets and how cool they are
3) Derive angular quantities from basic linear kinematics
4) Learn about torque as an analogy to force
5) Derive the conservation of energy with rotation

Visit my youtube channel for a video demonstration of my trebuchet: Lego Trebuchet DIRECT HIT .



- Lego
- String
- Paper
- Rubber band
- Copper weight (100 g)
- Plastic bead (2.6 g)

Building the trebuchet

1. Be creative (this can be made into a science challenge)!

2. To construct the tabletop trebuchet, build a sturdy frame using Lego Technic pieces, which is secured to a stable base made with regular Lego pieces (i.e. Lego bricks and planks). The base includes a firing chute (also made using Lego bricks) to maintain a straight firing trajectory.

3.The frame consists of two truss elements that are connected to a shaft. At the centre of the shaft rests a throwing arm that is free to rotate. A long Lego pin is slotted into the throwing arm to act as an arm extension. The throwing arm can be extended to any desired length.

4. The trebuchet frame is then mounted on a flat foundation to prevent sliding as the trebuchet recoils after launching a projectile.

5. The counterweight of the trebuchet consists of a box (made of Lego bricks) that houses a 100-gram copper weight. To prevent the box from collapsing whenever the counterweight falls, secure it with a rubber band.


I would like to thank Dr. Kotlicki and Dr. McKenna for running the course and for providing constructive feedback.

I would also like to thank my fellow classmates for providing constructive feedback that helped me improve my project.