Equipment:
Theory: A rocket gains momentum by ejecting matter at high speed out the back. If the system is stationary to start with, the net momentum of the rocket at any time is equal and opposite to the net momentum of the ejected mass.
Description: The rocket is simply a holder for a CO2 cartridge mounted on a counter-balanced arm that is free to rotate. Place a CO2 cartridge in the holder, arm the firing pin, place the firing pin next to the cartridge, and fire when ready. The CO2 gas escapes at high speed, making the rocket spin quite quickly; make sure you move your hand out of the way after firing the rocket.
Setup time: 5 minutes