Home Activity: Alka Seltzer Rockets

A new activity at this year’s STEM events is Alka Seltzer Rockets. This is a fun way to learn about about chemistry and see Newton’s 3rd Law of Motion in action!

The supplies are simple:

  • Alka Seltzer tablets
  • Film canisters
  • Water

We’re doing this in the school gym with a mop on hand for easy clean up, but at home, it’s better to do this outside:

  • Before going outside, cut the Alka Seltzer tablets into 4 or 5 pieces
  • Fill a film canister about halfway with water
  • Place a cut piece of Alka Seltzer into the canister
  • Cover the canister with the lid – make sure the lid is completely on to form a tight seal
  • Turn the canister upside down (lid on the bottom) and place it on the ground
  • Step back several feet and watch it take off!

What caused the “rocket” to pop up? Combining the Alka Seltzer (which has citric acid and sodium bicarbonate) and water starts a chemical reaction that creates bubbles of carbon dioxide gas. As the gas builds up, it’s trapped in the canister (if the lid is on tightly). The pressure from the gas increases until it’s too much for the lid and POP! The canister flies up like a rocket! This is a great example of Newton’s 3rd Law of Motion – “Every action has an equal and opposite reaction.” As the carbon dioxide forces its way out the bottom of the canister, the canister then propels upward in the opposite direction. This concept applies to all rockets whether it’s launching film canisters or launching Elon Musks’ Tesla Roadster into space!

Safety is important! At events, we have a launch area and safety perimeter around it which kids can only cross when placing their rockets down. The kids aren’t otherwise allowed to cross the safety zone. Only the volunteers in charge of the rockets who are wearing safety goggles are permitted to check on unlaunched rockets or retrieve empty canisters. You can decide the best way to do this at home, but always keep safety in mind.

If you want to make this activity into more of an experiment, you can vary the amount of Alka Seltzer in the canister. With 1/4 to 1/5-sized pieces, expect the rockets to launch 4 to 10 feet in the air.

If you want to make this into more of a STEAM activity, you can make the canister look more like a rocket using a 5″ x 8″ index card, crayons or colored pencils, tape, and scissors.

Let us know how far your rockets went!

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