1. Sealed Can: When a can of soda is sealed, it contains carbon dioxide (CO2) gas under high pressure. This pressurised CO2 is dissolved in the soda liquid.
2. Opening the Can: When you open the can, you provide a pathway for the dissolved CO2 to escape. The pressure inside the can is suddenly reduced, causing the dissolved CO2 to rapidly come out of solution.
3. Formation of Bubbles: As the CO2 rapidly leaves the liquid, it forms tiny bubbles throughout the soda. These bubbles rise to the surface, creating a fizzy effect.
4. Sound Production: The rapid release of CO2 creates a turbulent flow inside the can. This turbulent flow and the vibration of the can walls produce a distinctive "psst" sound when the can is opened.
5. Foam Formation: The escaping CO2 bubbles mix with the air and can create a layer of foam on the surface of the soda.
So, the "psst" sound when you open a pop can is primarily due to the sudden release and expansion of dissolved carbon dioxide gas, causing bubbles and turbulent flow inside the can. This phenomenon is common in carbonated beverages and is part of the experience of enjoying a fizzy drink.