# Canister Rocket

Rockets rely on newton’s 3rd law to propel themselves into space. Newton’s 3rd law states that every force has an opposite and equal force. For example, if you push on a wall, the wall pushes back on you with the same force. Similarly, as rockets ignite and expel fuel, the engine applies a force pushing the fuel out of the rocket.

Because the rocket applies a force on the fuel, the fuel also applies the same force back onto the rocket. The force that the fuel applies to the rocket is the upward force that propels it into space. With this demo, you can make your own rocket-propelled film canister with a few household items.

Image Credit: steakpinball/grafixtek via flickr.

### What You Need

• Water
• A film canister
• Construction paper with your favorite color
• Protective eyeware

### What to Do

• Roll a piece of construction paper around the film canister so that it makes a long cylinder.
• Make sure that the open end of eth film canister points away from the paper body of your rocket
• Put on your safety goggles
• Fill the film canister about 2/3 with water
• Place an Alka-Seltzer tablet in the lid of the canister
• Seal the lid onto the canister and give it a quick shake
• Place the rocket on the ground (cap pointing toward the ground) and stand back
• Watch the rocket explode off the ground and launch into the air!

### What's Going On?

The Alka-Seltzer and water react to form CO2. As CO2 concentrations build in the film canister, the pressure inside of the canister increases.  Once the pressure is high enough to pop the top off of the canister the rocket will shoot into the air.  All of the CO2 that was inside of the canister is being forces downward by the canister’s walls.  Because the canister’s wall exerts a downward force of the CO2 the CO2 exerts an upward force on the canister.  This upward force propels the canister rocket into the air.

### Questions

• Is there a minimum amount of water needed in the canister to make it launch off the ground?
• Is there a minimum sized Alka-Seltzer tablet required to launch off the ground?

- Matthew Goszewski