Fizzy drinks contain carbon dioxide dissolved under pressure. Shaking the bottle creates many tiny bubbles and gives the gas places where it can come out of solution. While the bottle is closed, the gas is trapped and the pressure remains high. When the lid opens, the pressure above the liquid suddenly falls. Carbon dioxide then leaves the liquid rapidly and existing bubbles expand. Rising bubbles push liquid upwards, which can produce the familiar spray. Waiting allows some bubbles to disappear and the drink to settle, reducing the number of rapid bubble-growth sites when it is opened.

The effect becomes easier to notice when conditions change. Temperature, pressure and particle motion can alter how quickly processes happen or how matter behaves. Food storage, refrigeration, cooking and weather all give everyday ways to test the same particle ideas without needing specialist equipment.

A gas is made of particles moving rapidly in random directions. Pressure comes from those particles colliding with the walls of their container and changing momentum. Heating the gas makes the particles move faster, so collisions become more frequent and harder; if the volume cannot increase, the pressure rises. If the gas can expand, pressure, volume and temperature all become linked.