What you need: a jar of clear fizzy drink, a jar of water, a handful of raisins
What to do:
Drop a handful of raisins into the jar of water. They will sink to the bottom,
Drop a handful of raisins into the jar if freshly opened fizzy drink.
After a while the raisins will rise to the surface, sink, rise again thus dancing up and down.
What we learned:
The raisins are heavier than the drink so they sink to the bottom. At the bottom of the fizzy drink they collect bubbles of carbon dioxide and now the raisins and bubbles are lighter than the drink so they rise to the surface.