Raisin lift

The raisins first sink to the bottom of the glass. Glass bubbles then collect there and the raisins rise to the top. When the bubbles burst on the surface, the raisins sink back down and the game starts all over again.

Fill the glass with mineral water and add 5 to 10 raisins.

• Mineral water,
• a glass of water,
• some raisins,

What is technically behind the experiment

This experiment can be described in terms of buoyancy in liquids.

Raisins sink in "normal" water because their density is greater than that of the water.

The raisins experience additional buoyancy due to the accumulation of air bubbles.

This can be explained in different ways:

1. a raisin with the air bubbles attached is regarded as a body. The air bubbles increase the volume of the raisin-air combination. This means that more water is displaced, while the weight changes only insignificantly. More water displacement means more buoyancy.

2. it can also be said that the air bubbles reduce the average density of the raisin-air structure and at some point it falls below the density of the water. Then the raisins rise

3) A third possibility is that the many air bubbles on a raisin together experience such a large buoyancy that they can carry the raisins with them.

3 However, it is NOT possible to say that the raisins become lighter due to the accumulation of air bubbles. (This is probably the most obvious explanation given by children).