Taking principles developed by Greek philosopher Archimedes more than 2,000 years ago, students constructed their own Cartesian Diver to study the relationship between buoyancy and density.
The Cartesian Diver is named for 17th century French scientist René Descartes although his connection to the experiment has never been found. A more correct name might be the Maggiotti Diver since it was Galileo’s student Raffaelo Maggiotti who claimed to have invented the device.
In the modern version of the experiment, students take a plastic pipette (medicine dropper) and thread a metal nut onto the stem. This is the diver.
The diver is partially filled with water—just enough so it barely floats upright in a container of water.
The diver is inserted into a soft drink bottle of water and the bottle is capped.
Now the fun begins.
When the bottle is squeezed, the diver dips down deeper into the bottle. When pressure is released, it quickly rises back to the top.
Why does it happen? Added pressure on the bottle compresses the air in the diver. It becomes more dense and sinks in the water.
It’s the same principle fish use to sink or float when a muscle squeezes or relaxes around an air sac. Similarly, submarines can be made to rise or sink by pumping water in and out of tanks.