You crack open a can of soda and — pssshhht! — a cloud of mist escapes. Tiny bubbles race to the surface, tickling your nose. What are those bubbles, and why do they appear the instant you open the can?

The secret is a gas called carbon dioxide, or CO₂ for short. At the factory, workers force this gas into the soda under high pressure — like packing a suitcase so tightly the lid barely closes. The gas dissolves into the liquid, hidden, waiting.

Inside the sealed can, the CO₂ has nowhere to go. The pressure keeps it trapped in the liquid, like a crowd squeezed into an elevator. The gas molecules are packed shoulder-to-shoulder, dissolved and invisible.

The moment you pop the tab, you break the seal. The pressure drops instantly. It's like opening the elevator doors — suddenly, there's room to escape! The CO₂ molecules rush out of the liquid and become bubbles of gas.

But here's the thing: gas bubbles need a place to start forming. In perfectly smooth liquid, they'd struggle to appear. So they look for tiny rough spots — a scratch on the glass, a speck of dust, even the bumpy surface of an ice cube.

Once a bubble starts, more CO₂ rushes to join it. The bubble grows bigger and lighter, then breaks free and zooms toward the surface. Hundreds of bubbles do this every second, creating that fizzy rush.

When the bubbles reach the top, they pop and release the CO₂ into the air. That's the fizz you hear and feel. If you let a soda sit open for hours, all the gas escapes — and you're left with flat, still liquid. No pressure, no fizz.

So the next time you open a soda, listen for that pssshhht. It's the sound of a thousand trapped gas molecules finally getting their freedom — and throwing a tiny, bubbly party on the way out.