Film Canister Launcher

Pressure from expanding gas made with simple materials pops a lid or launches a film canister

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What happens when you have a build-up of gas? Wait! Don’t answer that question! The gas used here is carbon dioxide (CO2), it comes from Alka-Seltzer, and the mess it makes is nothing short of fun. Warning: It’s impossible to do this activity just once. It is addicting and habit-forming. Proceed at your own risk!


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Here's What You'll Need

  • A film canister with a tight-fitting lid
  • Alka-Seltzer tablets
  • Water
  • Adult supervision

Let's Try It

  1. Put on your safety glasses! Half-fill the film canister with water.

  2. Divide the Alka-Seltzer tablet into four equal-ish pieces.

  3. Drop in one piece of the tablet and quickly snap the lid on the container. Give the canister a quick shake and set it on the table.

    Load the canister again, put the lid on, and turn the canister upside down. You can probably get two or three explosions from the tablet piece if you can can quickly snap the lid back on and enough water remains in the canister.

How Does It Work

The fizzing you see when you drop an Alka-Seltzer tablet into water is the same sort of fizzing you see when you mix baking soda and vinegar. In Alka-Seltzer, its citric acid and sodium bicarbonate that are mixing to produce bubbles of carbon dioxide gas or CO. When you drop the tablet in water, the acid and the baking soda react to produce the gas, and this gas keeps building up until finally the top pops off or the canister launches.

We can thank Sir Isaac Newton for explaining what happens. When the build up of carbon dioxide gas is too great and the lid pops off, Newton’s First Law is obeyed. The lid is stationary (not moving) but the growing gas pressure under it applies a large enough force to move it from it place. The upside down film canister shoots upward because of Newton’s Third Law of Motion. Gas inside the canister escapes and pushes against the table. The table pushes back with the same force sending the canister upwards briefly.

Science Fair Connection

Making Film Canisters “pop their top” is a pretty cool activity but it’s not a science fair project. You create a science fair project by identifying and testing variables. A variable is something that might change the outcome. Let’s take a look at some of the variable options you might test and write up for a science fair.

  • Test liquids other than water. What’s different about a reaction using orange juice, milk, soda, vinegar, coffee, tea, etc? Which of these liquids cause a reaction? Which is fastest? slowest? not at all? What’s the same about each test? What’s different? How long does the reaction take for each one?
  • There are many different kinds of water to test, e.g. tap, bottled, sparkling, distilled, spring, rain, different concentrations of salt water and/or sugar water, etc.
  • What changes do you detect in the reaction using colored water?
  • What’s combination of water and tablets causes the highest launch? the longest lasting flight? the loudest pop? What if you launch a canister from a plastic tube instead of freestanding?
  • What happens to the reaction time if you raise or lower the temperature of a test liquid? Write down your observations. You may need to experiment with several different film canisters until you find one that really pops.

These are just a couple of ideas and you certainly aren’t limited to them! Come up with your own variable to test. Remember, you can change only one variable for each test while making sure that all the other factors in your test remain the same!

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