Dancing Raisins Experiment
This is a classic and very fun experiment.
It teaches about buoyancy. The raisins start off as heavier than the soda and drop to the bottom of the glass, but then the bubbles from the carbonated soda stick to the pores in the raisins, and make it lighter than the soda. The raisin will float to the top of the glass, and then the bubbles pop, which again makes the raisin heavy, so it sinks, and then rises on and on until there are no more bubbles.
Try it yourselves at home!