- a plastic bottle filled with water, and a screw-top
- plastic pen top
- some modeling clay
- Stick the pen top into the piece of clay.
- Put the pen top in the bottle and seal the bottle tightly with the screw top lid. The pen top floats!
- Now squeeze the sides of the sealed bottle. The pen top sinks! Release the bottle, and watch the pen top float back up!
Why do you think the diver sinks when you squeeze the bottle?