Left Below: The professor fires the high speed CO2 gas one direction and is pushed along, like a rocket, in the other direction. Note that he is holding the fire extinguisher so that the force on him will act close to his center of mass. If he failed to do so he would start to rotate (out of control) in addition to translating. (Check out the next demo to see what would happen.)
To see a video of this demo click here
To see an short video of this demo click here.
Right Below: When one fires the fire extinguisher into a board attached to a cart the push on the fire extinguisher is balanced by the push on the board and no motion occures.
To see a video of this demo click here.
A fire extinguisher usually has a tip that channels the gas into equal and opposite jets (with canceling forces) so that the fire extinguisher can be used safely without recoil. A close-up of the tip and the opposing jets are in the picture above.
To see a video of these opposing jets click here
Intro-level lecture transparencies on various topics related to the rocket demo can be viewed by clicking the links below.
Quantitative calculation of velocity, acceleration and force.
Newton's force reaction force (2'nd) law and momentum conservation.
Quantitative application of momentum conservation.
