A weighted pen lid or condiment packet placed in a sealed water-filled bottle floats or sinks depending on the pressure applied to the bottle.

1. Fill a clear plastic bottle about three-quarters full with water.
2. Place a condiment packet or pen lid weighted with paper clips into the bottle, making sure it just barely floats.
3. Add more water until the bottle is completely full and screw the cap on tightly.
4. Squeeze the sides of the bottle firmly and observe what happens to the packet.
5. Release the pressure and observe the packet again.

Cartesian Divers - ScienceOnline:

The Cartesian Diver - Hungry SciANNtist:

📄 Cartesian Diver - ACN: https://www.acs.org/education/activities/cartesian-diver.html

• Use different types of condiment packets to see which works best.
• Try using a glass eyedropper or a plastic pipette with an air bubble as the diver instead of a condiment packet.
• Experiment with bottles of different sizes to see how it affects the diver’s movement.

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• What happens to the air bubble inside the condiment packet or pen lid when you squeeze the bottle?
• Why does increasing pressure make the packet sink?
• How does releasing the pressure cause the packet to float again?
• Would the diver behave differently if the air bubble were larger or smaller?
• How does this experiment relate to real-world concepts of buoyancy and density?