Created by Dale Olive
Future Flight Hawai`i instructor
Demonstration at a glance:
An Alka-Seltzer® tablet is placed into a film canister, which has been designed like a rocket. When water is added and the cap put on, the rocket is placed on the ground and within seconds shoots 20 feet into the air.
Take a clear film canister (these seal better than the black ones) and tape a rolled index card or paper around it to form the fuselage. Be sure that the open/cap side of the film canister is facing out as this is where the fuel will eventually go. Be sure to tape the film canister to the fuselage or the canister will launch inside the fuselage instead. Nose cones, fins and decorations can be added if you like. Once the rocket is completed, all that is needed is some water and Alka-Seltzer® tablets (or generic equivalent). I put in about a teaspoon of water and 1/4 to 1/2 tablet of Alka-Seltzer®. Quickly place the cap on and place on the ground. Be careful with students as the rockets do take off with quite a bit of force and a sharp nose cone could do damage. I have students wear safety glasses just in case (they really like wearing them anyway). When approaching a rocket that didn't take off I usually knock it over first to "defuse" it.
Alka-Seltzer® decomposes in water to form carbon dioxide gas. The gas builds up pressure until it has enough to push the lid off and fly upwards. It's a good example of Newton's third law: "action/reaction."
This activity could easily be turned into a lab or science project. I find it hard to measure vertical distances with younger students so we shoot them off in plastic cups held in a horizontal position. We then measure the distance they traveled horizontally from the cup to wherever it lands. Variables that could be looked at include: Does varying the amount of water make them fly farther? Does the amount of Alka-Seltzer® affect distance? Does the temperature of the water affect how far it flies? Do other liquids such as vinegar affect the distance? Does the angle it is shot at affect its distance? I've fired multi-engine alka-rockets but it takes good timing and the added weight usually prevents the dramatic desired results. I'd love to see a multi-stage rocket where a smaller rocket shoots out of a larger one while it is in flight.
Communications: Hawaii Space Grant Office
This activity is featured in Future Flight Hawaii, a K-12 Education Project of Hawaii Space Grant Consortium.
FEB 27 2001.