Get a jar and fill it with water, balloon, elastic band, bit of lemon. Put the lemon in the jar of water and put the balloon around the top of the jar. Put the elastic band around as well and screw the lid on.
You can make a Descartes "diver" or "devil" and here's how:
- Get a large empty plastic soda bottle and cap, and a glass medicine dropper.
- Fill the bottle with water almost completely.
- You'll have to adjust the amount of water and air in the dropper by simple trial and error so the dropper barely floats at the water level.
- Tighten the cap on the bottle.
- Now, by pressuring the plastic bottle you will able to make the dropper sink and rise at will.
