Demos: 1H-03 CO2 Rocket

The demonstrator is seated on a sturdy stool on a low friction cart. The nozzle of a large fire extinguisher is pointed away from the demonstrator (toward the side wall) and activated. The cart is accelerated backward and can reach significant speeds.

Directions: Aim the nozzle of the fire extinguisher at a slight angle away from straight ahead to avoid sending the CO₂ stream directly toward students sitting in the front row. Lean the fire extinguisher back slightly to brace it against the stool. Press the lever and hold it down until you have achieved the speed that you wish to travel across the floor, then release the handle. You can stop yourself with your feet, or crash into the opposite wall!

Suggestions for Presentation: First stand on the cart and tell the students to imagine that you have a pile of bricks available on the cart. How would you use them to get yourself moving? Discuss what throwing a brick would do. What if you threw another, then another? Now suggest smaller bricks thrown faster and more frequently. Reduce the bricks to molecules and discuss what will happen when the fire extinguisher rapidly “throws” out CO ₂ molecules. This is a crowd-pleaser and it is recommended that you do this as a finale to the lecture!

Applications: Rocket propulsion. You might discuss whether the air in the room has any influence on the propulsive force. (Students often believe that the rocket exhaust has to push against something. Point out that the propulsive force is actually more efficient in the vacuum of space.)

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