In my opinion, if you want a kid to become interested in science, all you need to do is launch something several feet into the air. Making a film canister rocket fits the bill perfectly as a simple experiment for kids that they will absolutely love.
It is best to launch film canister rockets outside. Be sure to stand back a few feet and wear safety glasses. You never know how high the canister rocket is going to fly!
Update: After we made our first Alka-Seltzer film canister rocket we got a little bit hooked. Since the first edition of this post was written we have used film canister rockets to make interesting firework paintings and we have used dry ice instead of Alka-Seltzer to launch the canister rockets. There are so many ways to experiment and have fun with exploding film canisters!
How to Make a Film Canister Rocket
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Assembling a film canister rocket is very simple. I gathered the following supplies:
- A plastic bottle with a snap top. The little canisters that hold 35 mm film work the best, but I couldn’t dig any of those up this time. I used a different snap top bottle and it worked fine. (I used these Airborne canisters that I found in the pharmacy, but I have also used M&M’s Minis canisters. There are definitely ways to make Alka-Seltzer rockets without film canisters!)
- Alka-Seltzer tablets
- Optional: Thin cardboard to make fins and a nose cone for the canister rocket. We cut up an old cereal box.
I cut out fins and a nose cone for our canister rockets. I attached the them with tape to the canister, but I’m thinking that got glue probably would have worked better. If you choose to make fins and a nose cone, make sure to attach the nose cone on the bottom of the bottle so that the cap-end is facing down at launch time.
We headed outside with the canisters, some water, and a handful of Alka-Seltzer tablets.
Some experimentation may be necessary to figure out the best ratio of water to tablets to add, but experimentation and learning is what we’re all about, right?
We had the most success with filling up the film canister with water, leaving about 1/2 inch of head space at the top. We dropped in one Alka-Seltzer tablet, quickly snapped the bottle close, and stood back!
After some serious fizzing, bulging, and leaking, the film canister rocket launched off the ground!
If you find that one tablet wasn’t enough to make it launch, try it again with two tablets. Or fill the bottle up with more water. Some experimentation may be necessary, but that’s all part of the fun!
You can always experiment to compare how it works with cold water versus hot water, how it works right side up versus turning the bottle upside down, etc. Record your findings and leave a comment letting me know what you found!
Film Canister Rocket Experiment
So what makes the explosion happen? It is actually the same chemistry that happens when you mix baking soda and vinegar together. An acid plus a base mix to form carbon dioxide gas, which are the bubbles you see. When enough carbon dioxide has been produced the pressure builds until the container can no longer contain it, at which point the top pops off and the gas and liquid explode out.
Alka-Seltzer is made of citric acid and sodium bicarbonate (baking soda), which acts as a base. When the tablets are solid and dry the acid and base don’t react, but as soon as they are immersed in water they react to form carbon dioxide. This is what causes the explosion. You can even alter this activity just a tiny little bit to make your own lava lamp! (No explosion there, just cool colored bubbles.)
Alka-Seltzer Film Canister Rocket
We have film canister rockets several times now. The first time we did it as part of a unit study on volcanoes. I wanted to show the kids that when the pressure builds up under the earth’s crust it can literally blow the top off of a mountain in a volcanic eruption. (This is how Mount St. Helens exploded in 1980.) This video below illustrates that explosion very well.
Experiment to see what happens when you add more/less water, vary the temperature of the water, add more/fewer tablets, etc. The results may surprise you!