A Cartesian Diver is a (plastic) bottle with an eyedropper in it. The eyedropper is partially full of air. When you squeeze the bottle, the air compresses and the dropper sinks.
- 2 liter bottle
- sink area to construct it
- Clean bottle. Remove the label from it.
- Fill the bottle with water first. Start with the dropper full of air, then add more water slowly. Test it often, so that you don't accidentally let the dropper sink to the bottom, since it will be annoying to get it back out. You want it to just barely stay afloat, but it isn't super-sensitive.
- Ideally, the water level will be in the glass area, not in the rubber bulb. This way, you can see the water level change as you vary the pressure. To get around a water level in the bulb, I put a rock in the bulb, which increased the mass enough to lower the water level into the stem. It takes a bit of guessing-and-checking.
- To go along with this, you could get a small plastic bottle, put some water in it, head it up to turn it to steam, seal the bottle and let it get crushed. When I used a polyethelene drinking water bottle, the heat seriously weakened the plastic, but didn't break it, only exaggerated the crushing effect. (I have been able to crush a polycarbonate bottle before, but it's hard. It sprung back pretty easily.) If you were more adventurous, you could try exploding a bottle.