Unlike a balloon rocket, most rockets create the gas they need for thrust via a chemical reaction. A fuel (like liquid hydrogen) is mixed with a source of oxygen (often liquid oxygen) and burned in a chemical reaction that produces a lot of gas! In this project you can make a simple rocket and fuel it by a chemical reaction that produces carbon dioxide. Make sure you launch this messy rocket outside!
The Alka-Seltzer reacts with water to produce carbon dioxide. When enough carbon dioxide is produced to create pressure on the inside of the canister, it will force the lid to pop off so the gas can escape. As the gas escapes the rocket is propelled upward.
Try to measure how high your rocket goes compared to a nearby fence or a tree. Try it several times; do you get the same results each time? Does the rocket go higher if you add more or less water? Why do you think this is? What happens if you change the design of your fins or nose cone?
Now try it again with a different type of fuel. When vinegar and baking soda are mixed together, they produce carbon dioxide. Experiment to see how much baking soda and vinegar will launch the rocket the highest. (Some tips: You can either pack the baking soda in the lid with a damp thumb so that the reaction doesn't start until you turn the rocket over, or you can wrap it in some tissue paper or toilet paper to delay the reaction starting and give you time to set the rocket right-side-up.)