aka...science room
fizzy pop
The bubbles in fizzy pop are bubbles of carbon dioxide. Carbon dioxide is forced into the liquid and trapped there by sealing the can under high pressure.
When you open the can, the pressure inside it is suddenly lowered and a rush of carbon dioxide gas leaves the liquid – this is the hiss that you hear.
But not all of the carbon dioxide leaves at once. Bubbles of carbon dioxide gas continue to rise through the liquid and this is the fizz.
Flat pop
However, there is only so much carbon dioxide in the pop. It does take some time for all the gas to leave the liquid but eventually you are left with flat, rather than fizzy, pop.
If you have an open can of fizzy pop that you want to save for later, put it in the fridge. It takes longer for gases to leave a cold liquid than a warm liquid so you have a better chance of still having fizzy pop later in the day.
Does tapping work?
Opening a can of fizzy pop after it has been shaken or dropped can be spectacular. The rise in pressure caused by the shaking means that the gas tries to escape very quickly and pushes lots of the liquid out of the can in its haste.
Tapping the can before opening it forces most of the trapped gas bubbles to the surface of the liquid. This means that the gas can escape easily and quickly when the can is opened, without having to push a whole load of liquid out of the way first.
Contrary to various superstitions there is no exact number of times you have to tap the can!
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