This is a simple experiment you can try in your kitchen at home.

Tall clear glass
Clear fizzy drink, like lemonade
Handful of raisins

1. Pour the fizzy drink into the glass.

2. Drop the handful of raisins into the glass.

3. Watch and wait!

As if by magic, the raisins rise and fall!

When you first put the handful of raisins into the glass, the raisins sink because they are more dense (heavier) than the drink. If you wait a minute or two, bubbles begin to stick to the raisins. The bubbles are carbon dioxide gas. When the raisins are covered in bubbles, they are less dense (lighter) than the drink and they begin to rise.

As soon as the raisins reach the top of the glass, the gas bubbles burst and the raisins begin to sink again. The raisins should continue to rise and fall for about an hour.

Do the experiment again, but this time drop other items in a glass of fizzy drink, like peanuts or popcorn kernels.

Does the experiment work now?

Sometimes, scientists aren't just concerned with how heavy or light an object is - they are also concerned with how much space it takes up. They use the word DENSITY to describe this. Density also helps us to work out whether an object will sink or float.