Premise: A sodium bicarbonate rocket (sometimes called an Alka-Seltzer rocket) is a model rocket fashioned from a 35mm film canister and propelled by the pressure of a gas, often carbon dioxide, generated from the reaction of an acid with sodium bicarbonate. Sodium bicarbonate rockets are often used in science classes to demonstrate principles of chemistry and physics.
Hypothesis: they use 40mm film cannisters to make the rockets