Inside the canister, two things meet for the first time: water and an effervescent tablet. The tablet contains two dry chemicals — citric acid and sodium bicarbonate — kept separate until water arrives. 

The moment they combine, they trigger an acid-base reaction that produces carbon dioxide gas rapidly — the same type of reaction as [Exploding Jellyfish] and [The Invisible Fire Extinguisher], just packaged into a tablet.

Here's the critical part: the canister is sealed. The gas has nowhere to go, so it builds up inside, pressing outward against every surface. This is pressure — and it grows with every second. The lid is the weakest point. The moment the internal pressure becomes too great, the lid gives way.

Gas blasts out one way — downward. Newton's Third Law says that for every push in one direction, there must be an equal push the other way. The canister shoots upward. You see the same law at work in [Balloon Rocket Blast-Off] — different fuel, identical physics.

Real rockets do exactly the same thing — except instead of CO₂ from a tablet, they burn fuel and blast hot gas downward at tens of thousands of kilometres per hour. Bigger push down. Bigger push-up. All the way to orbit.