STEM Adventures: Alka Seltzer Rockets – 8/11/20

Today in STEM Adventures, we’re becoming astronauts and making Alka Seltzer rockets!

To complete this challenge, you will need

• A water bottle
• Alka seltzer tablets
• String, foam, gems, or other decorations
• A small canister with a lid (a film canister might work well)
• Goggles
• Hot glue
• Water

Directions:

1. Make sure your water bottle is empty and dry. I’ve found that the smaller water bottles, like the 12 fl oz. ones, work best.
2. Decorate your rocket with foam wings, streamers, string, gems, or other items. Remember how we talked about drag and wind in the NASCAR Acceleration Nation and Rapunzel STEM Adventures classes? Keep that in mind when putting together your rocket.
   • The neck of your bottle will be where you launch your rocket, make sure not to cover it.
3. Grab your canister, some water and your Alka Seltzer tablets and head outside. Here is where the real fun begins.
4. Put your googles on. This is a very important step for this project. Remember what Woody and Buzz say in Toy Story: “I just lit a rocket and rockets explode!” Your rocket might not explode but it is a projectile and your eyes need to be protected.
5. Fill your canister 1/3 of the way with water.
6. Quickly drop in 1/2 an alka-seltzer tab and snap the lit on your canister. Set your rocket on top of the canister and take three giant steps back. Make sure your rocket isn’t pointing at anyone. If it is, tell them to get out of the way.
   • If your rocket falls of the canister don’t go back and try to fix it. Let the reaction happen and try again when it is over.
7. If all goes as planned (and sometimes with this experiment it doesn’t) a reaction should happen within the canister, the bottom should pop off and your rocket should fly.

This experiment is tricky because it’s about timing a quick reaction to work just right, and making sure everything works perfectly in a timely manner. This can be both exciting and stressful! If you’re worked up over this STEM experiment, imagine how real engineers at NASA feel when they are launching a spacecraft, especially one with astronauts inside!

Assuming your project goes off without a hitch, what’s making it work?

When the alka-seltzer tablets fizz in the water, they release carbon dioxide gas. The gas builds up inside the confined, small space of the canister until the pressure is too much and it eventually pops the lid off.

The lid is the canister’s weakest point, and when it pops off, all the gas rushes out of the opening. Newton’s Third Law of Motion comes into play here: “Every action has an equal and opposite reaction.” Because the gas is rushing out of the bottom of the canister, down toward the ground (the action), the rocket and the top of the canister go up (the equal and opposite reaction).