Question: what makes coca-cola fizzy?

Sara Imari Walker answered on 14 Jun 2011:

Great question! Especially since I love coca-cola, it is really tasty with all those bubbles in there!

Coke like all sodas has carbon dioxide gas dissolved in it. In a closed bottle, the soda is under pressure, and so the gas cannot escape the soda. But something cool happens when you open the bottle. Opening the bottle releases the pressure and the gas begins to escape. We see this when we watch the bubbles rising. If you leave the bottle open for a while, all the gas will escape and the soda goes flat. If you seal it back up, then the pressure builds back up inside, and keeps the gas dissolved in the soda, so it stays nice and fizzy. So if you like that nice fizzy taste, best to keep your soda covered!