Step 2: 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
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?