Open the soda.
Add a few raisins (or pour soda into a cylinder or tall jar, then add the raisins).
Watch them rise and fall.
The soda water is water with carbon dioxide gas dissolved in it.
The carbon dioxide in the soda comes out of solution and attaches to the raisins.
This decreases their overall density, so they float to the surface.
At the surface, the bubbles pop, the raisin becomes more dense than the liquid again, and sinks.
The cycle repeats.
The activity can be extended:
1. Ask students to cap their bottle and watch. The raisins will slowly stop dancing. The gas pressure in the air space at the top of the bottle prevents as much carbon dioxide gas from coming out of solution. When the cap is released the raisins will start dancing again as gas is able to come out of solution once more, and sticks to the raisins. This capping and uncapping cycle can be repeated.
2. Ask students to shake their bottle, then slowly release the cap to expel the released gas. With less (or no) gas in solution, the raisins will not dance as fast (or at all).
Use room temperature soda. Does not work with fridge-cold soda. I assume the gas does not come out of solution as easily, so that fewer bubbles attach to the raisins.
Lentils move faster to start, but get soggy more quickly.