Explanation

Fizzy drinks are fizzy because they have had a lot of carbon-dioxide (CO 2 ) dissolved in them under pressure. When you release the pressure by opening the lid, this carbon-dioxide then comes out of the solution and forms bubbles. It is hard for gases to form bubbles in the centre of a glass of water because surface tension crushes them before they can grow large enough to be stable (Find out more in the

lemonade volcano experiment).

This means that bubbles tend to form on the edges of the water, ie on the bottom of the glass, and on your raisin. If you look carefully you can see them growing larger and larger.

The fizzy drink has a lot of dissolved carbon-dioxide, which forms bubbles more easily on surfaces like the glass and the raisin. The bubbles stick to the raisin and grow. The bubbles float and eventually overcome the raisin's weight, and it floats upwards.

Eventually the bubbles make the raisin float and it moves upwards to the surface, where some of the bubbles pop and the raisin sinks again.