Build a Pop Rocket

How to Build Your Own Pop Rocket

We're going to launch a pop rocket by building up pressure using a chemical reaction.

I really I really like this activity because it challenges kids to think outside the box. Most kids initially see the water and tablets as 'fuel' and assume that the more they use, the higher it will go (which is actually the opposite of what really happens). Kids get to hone their observation skills as they try different variations to get their rocket to land on the roof.

I also really like this experiment because it combines chemistry, gas pressure, and Newton‘s laws of physical motion all in one cool experiment.

Materials:

  • Water
  • Alka-seltzer tablets
  • Fuji film canister (or m&m container or any container with a tight fitting lid or cork)

Experiment

Be careful with this! These rockets can wind up on your roof, so do this activity outside and away from structures.

  1. Fill your container partway with water
  2. Drop in a tablet
  3. Working quickly, cap the container and invert it so the film canister is bottom-side up. If you‘re using a cork and bottle, stand the bottle right-side up so that the cork is the thing that flies off.

Experiment with different amounts of water and tablets to see how high your rocket can go. You can add a nose and fins
using hot glue later.

What's Going On?

For every action, there is equal and opposite reaction. If flames shoot out of the rocket downwards, the rocket itself will soar upwards. It's the same thing if you blow up a balloon and let it go-the air inside the balloon goes to the left, and the balloon zips off to the right (at least, initially).

Your rocket generates a high pressure through a chemical reaction. The alka seltzer and water combine to form carbon
dioxide gas (CO2) which builds until it pops the lid off your film canister. The lid flies one way and the tube goes the other. Newton's Third Law in action!

You don't have to just use alka seltzer and water... what about baking soda and vinegar? The combination of those two
also produces carbon dioxide gas.

What other chemicals do you have around that also produces a gas during the chemical reaction? Chalk and vinegar, baking soda, baking powder, hydrogen peroxide, isopropyl alcohol, lemon juice, orange juice...?

You can also modify your rocket body design. Add foam fins and a foam nose (try a hobby or craft shop), hot glued into
place. Foam doesn't mind getting wet, but paper does.

Put the fins on at an angle and watch the seltzer rocket spin as it flies skyward. You can also tip the rocket on its side and add wheels for a rocket car, stack rockets, for a multi-staging project, or strap three rockets together with tape and launch them at the same time! You can also try different containers using corks instead of lids.

This experiment is a prime example of Newton‘s Third Law of Motion: for every action there‘s an equal and opposite reaction. When the film top flies off in one direction (usually held into place by the floor), the rocket body shoots in the opposite direction.

Questions to Ask

  1. Does water temperature matter?
  2. Do crushed tablets work better than whole pieces?
  3. How many tablets can you add at once?
  4. What if you use vinegar instead of water? Soda water?
  5. Does more water, tablets, or air space give you a higher flight?
  6. What happens if you strap this rocket to a matchbox car? Which way does the lid go, and which way does the car move?