Step 2: Back to the pressure...

Picture of Back to the pressure...
Water rockets use air pressure to throw the water out of the rocket, but it doesn't have to be air. Alka-Seltzer (or 'A-S') rockets use gas pressure to throw water out the back, like the water-rocket, but you don't need so much equipment, so much effort, or even so much preparation. The easiest way to find out what we're talking about is to try it. Time for another experiment.

Take an 'Alka-Seltzer' tablet (or any other indigestion remedy with the word 'effervescent' on the packet) and drop it in water. See the fizz? That is carbon dioxide gas (CO2). The gas is produced by a chemical reaction between the solid ingredients of the tablet. Notice how the froth is a lot bigger than the original tablet? If we can trap this large volume of gas, we can create enough pressure to power a rocket.

Time to Build Another Rocket.

As with any experiment involving chemicals or fast-moving parts, safety must be observed. A-S rockets can be fast, so wear safety goggles, which also serve to prevent chemicals being splashed in the eyes. If you know you have an adverse reaction to aspirin (an ingredient of Alka-Seltzer), you should take extra care, or even avoid doing this experiment all together.

These rockets need some, ahem, highly technical equipment:

An Alka-seltzer tablet
A 35mm film canister
Some water

That's it. Really. The rocket is finished. There's nothing else to do except...

Launching the A-S Rocket

A-S rockets are best launched outdoors, as they can go higher than a typical ceiling, but if you have access to a large room with an easily-dried floor (school science lab, church hall, warehouse, etc) then go for it.

Launching an A-S rocket takes quick, nimble fingers. Put a small amount of water in the film canister (about a teaspoon full is a good start). Snap the tablet into four quarters, put on your goggles and get ready for the speedy bit:

Drop-the-tablet-in-the-water, put-the-lid-on-quickly, stand-the-canister-upside-down-on-a-surface-that-doesn't-mind-getting-wet and-stand-back.

The ingredients on the A-S tablet dissolve in the water, and the fizzing starts. CO2 is being generated and the pressure is rising inside the canister. Don't lean over it, because very soon the pressure will be great enough to throw the lid off and the water out backwards, sending the body of the canister flying upwards. There will also be a certain amount of splashing, so don't stand too close!

Alka-Seltzer Rocket Recovery

Now that it's empty, the canister is very light, so it doesn't need a parachute, and won't do any damage on the way down. Watch carefully as it falls, just in case a gust of wind carries it away.


> A-S rockets can become the heart of a lot of 'proper' Science:

> What are the ideal quantities of water and tablet to add?

> Will other combinations of chemicals yield the same effect (baking soda and vinegar?)

> Can streamlining improve the tumbling flight of the canister?

> Will other containers act as rockets as well? What about a fizzy pop bottle with a cork in?
redcrate3 years ago
Baking Soda and Vinegar is a lot more fun and costs less:

Kiteman (author)  redcrate3 years ago
This is a lot less messy, though, and (when you've got a class of thirty 11 year-olds doing this) it makes the risk-assessment paperwork easier to have water splashing instead of acidic vinegar.

Oh, and isn't it about time you posted another project? ;-)
Delo973 years ago
I've got an idea
Using some ultra-tech hi-cost toilet paper, you could separate the AS from the water... until it's flipped. Then, they would come in contact, and... BOOM! An instant, easy to carry AS rocket! Just take care not to flip it as an accident.
OMFG TOILET PAPER FTW!!1!!!11!!1!one!!eleven!!!!11!1!!!.png
Kiteman (author)  Delo973 years ago
Yes, that works well.
Delo97 Delo973 years ago
Also, sorry for the horrible drawing, it was done on MS Paint with a mousepad.
Whoa sweet Kiteman! Are you from the U.K? People from their are always cool =P
Kiteman (author)  thomasthetankengine4 years ago
I am.

Cool? I try.
Haha. I think you are one of the best people on Instructables right now! I love this website so much. Me and my friend were making Altoids Tin boats all day yesterday!
Kiteman (author)  thomasthetankengine4 years ago
I hope you took plenty of photos to write up a step-by-step Instructable?
Actually, we used this one that's already posted, then did a little tweaking and improv.


Sorry can't make links for some reason...my computer can but I forgot how. =) Copy and paste it?
_Scratch_6 years ago
Could u make a giant alka-seltzer rocket out of.... well let's say a 55 gallon steel drum?
You could, but lift off might be a bit of a problem. I would suggest using something a bit more powerful, with some way to focus it a little bit better.

(hides the bucket of thermite for later use...)
Kiteman (author)  _Scratch_6 years ago
Eyes glaze over...

I don't see why not...
Awesome, i think ill make a rocket powered 55 gallon drum car...... =P
Kiteman (author)  _Scratch_6 years ago
Don't forget to do an ible of it, and include a video of your first run.
Kiteman (author)  Kiteman6 years ago
(Seriously, do it.)
also, do you happen to know the PSI that a sealed pill bottle alka seltzer rocket would have? if the gas had nowhere to go.
BEAST146 years ago
AAAHHH!!! I'm about to cry! that picture is terrible yet irresistible!
Kiteman (author)  BEAST146 years ago
As I said to Jupitane; use red/green 3D glasses.
Jupitane6 years ago
That picture makes my eyes water.
Kiteman (author)  Jupitane6 years ago
Look at it through red-green 3D glasses...
Jupitane6 years ago
Look at all the words.....