Pop Science

A student tries to catch her flying canister, visible as a white spot in front of the sign over the door

Fifth graders on Monday took part in a hands-on demonstration of Newton’s Third Law of Physics. The students filled film canisters partway with water, added a piece of an Alka-Seltzer tablet, snapped the lid on the canister, then quickly placed it top-down on the ground. A build-up of pressure from the dissolving Alka-Seltzer popped the lid off, sending the canister as high as 20 feet into the air.  

Teacher Joseph Schneider (talking to two students in the photo) explained that Newton’s Third Law states that for every action, there’s an equal and opposite reaction. In this experiment, the Alka-Seltzer reacts with the water, producing carbon dioxide gas, which rapidly builds pressure in the container (the action). This pressure forces the lid off the canister, expelling the gas and water downward, which pushes the canister up with a force equal to the force pushing downward (the reaction). This experiment is sometimes called Fizzy Rockets.