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Trebuchet Physics

A Trebuchet is a siege engine that transfers gravitational energy into kinetic energy. (It takes the force of gravity and uses it to fling an object.) It does this by the use of a counterweight that falls.

You can think of a trebuchet as a see saw! Yes, a see saw is really all that a trebuchet is. On one end of the seesaw is a projectile you want to fire and on the other end is a counterweight. Raising the counterweight above the ground causes a build up of potential energy. When you release this counterweight and allow it to fall the seesaw pivots on the fulcrum and the other end (with the projetile) recieves the energy. This force of energy can be quite substantial and it is enough to send a projectile flying through the air.

How to calculate the velocity of your thrown projectile:

This is easily done with the formula of Velocity = (The rate of gravity) X (The time it takes for the projectile to drop

The rate of gravity is 32.2 feet per second

How to Calculate distance of throw:

Time how long the projectile stays in the air. This is "T" Now multiply this by itself. So if "T" is 4 seconds then you multiply 4x4 to get 16. Now times this by the force of gravity (32.2) And you get 515.2. Then you divide this by 2 and you get the distance. In our example it is 257.6 feet.

The formula is: Gravity times Time Squared then divided by 2

How it works

The projectile of a trebuchet travels in a Parabola
To attain the optimum amount of the transfer of energy the counterweight should be allowed to fall as vertically as possible to gain the most momentum from g (9.80 m/s squared).
To attain maximum range the release point should be between 40 and 45 degrees.
To gain more velocity (of course at the cost of distance) a lighter projectile will have a later release point and a flatter trajectory and thus more speed. The angle of the release hook may also be adjusted forward to attain the same result with a heavier projectile.
Why the wheels add energy: The wheels add more power because as the counterweight falls the whole machine moves forward slightly to "meet" the fall thus giving you a more vertical drop leading to more energy being transferred to the throwing arm.
He added Wheels to his design (You can see the wheels in the picture on the right). They give it a battlefield ready look and they added 25% more power! With the wheels on it this thing looks like it is ready to be rolled out on the battlefield. (The wheels add more power because as the counterweight falls the whole machine moves forward slightly to "meet" the fall thus giving you a more vertical drop leading to more energy being transferred to the throwing arm).

Experimental Data

The maximum range ballast/projectile weight ratio is 133:1 (2000 kg./15 kg.). Interestingly, Warwolf had the exact same ratio (40,000 lbs./300 lbs.).

This is a Storm The Castle Project