Trebuchet

Parts List and Overview

 

The trebuchet pictured above is armed and ready to throw an object.

Pulling the pin out of the trigger allows the counterweight to fall. The long end of the throwing arm swings up rapidly, pulling the sling forward.

The sling, with an object in its pouch, swings around the end of the throwing arm picking up speed.
When the throwing arm rotates past vertical, one end of the sling releases from the slot in the end of the arm.
This releases the object from the pouch allowing it to fly forward.

The physics of this ancient device is complicated involving gravitational potential energy, angular momentum,
velocity ratio and kinetic energy.

The Simple Explanation: 
When the counter-weight falls, its gravitational potential energy is changed to kinetic energy in the moving projectile.

A more detailed discussion of Trebuchet Physics: (Word document)

Trebuchet after "firing".

Parts:

 

Throwing Arm

All material is 3/4" softwood.

A - main base (1) - 9 cm x 30 cm

B - Base Supports (3) - 3.8 cm x 14 cm

C - Uprights (2) - 28 cm x 1.8 cm

D - braces (2) - 1.8 cm x 27.5 cm (long side, angle 45 degrees)

Trigger block

1.8 cm x 7.5 cm

1.8 cm slot cut in one end.

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