Video: Watch this demo
Description: This demo shows a very crude representation of how a rocket works.
As the material leaves the fire extinguisher, it produces thrust which propels you in the opposite direction.
Conservation of momentum can be explained here.
- Rocket Wagon
- Full fire extinguisher
- Helmet and “parachute”
- Adjustable wrench
- Using a full fire extinguisher, take the main hose off using the wrench.
- Connect the rocket wagon hose to the extinguisher using the wrench.
- Insert the extinguisher into the cart as shown in the picture.
- Include the helmet and “parachute”.
- Most professors like the surprise factor, so leave it just outside of the classroom in the lecture prep room.
- When the professor is done, take the fire extinguisher off the wagon and reconnect the original hose.
- Place the extinguisher with the other used ones in room 22.
NOTE: Please do not, for your safety and the well-being of the wagon, attempt a crash like this yourself.
- Give the lecture prep staff plenty of notice for this demo, as fire extinguishers are in limited supply.
- When ready, wheel the wagon into the class.
- Line the wagon up on the other side of the door, and make sure you have a straight line with nothing in the way.
- The exhaust port is on the back of the wagon. Make sure no students will be in back of the wagon during your whole trip (so you don’t shoot them with what’s in the extinguisher).
- There are no breaks, so consideration on how you will stop must be done beforehand.
- Break the seal on the fire extinguisher.
- Put on your safety helmet for a funny effect.
- Sit down on the wagon, with your two feet on the two wooden pegs. Take a hold of the wagon handle. Pull the safety pin out of the extinguisher.
- Hold the fire extinguisher handle in and you will start to move. Do not let go of the extinguisher handle until you want to stop.
- To stop, drag your feet and try not to run into something. For effect you can release the “parachute” (really cheesy).
- Explain to students that this is how a basic rocket works on principle.
- A common misconception for students is with conservation of momentum in that: Two objects can initially be at rest and together (rocket and rocket fuel), yet later both be moving while still having conserved momentum.
Note: This demo may be loud for some students, so it’s nice to give them a heads up.