Cartesian Diver

Let's take a look!

Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

• Materials required for the experiment: a dropper, a large nut (M6), a small nut (M5), and a cable tie.
• Insert the dropper through the small and large nuts.
• Use the cable tie to keep the nuts from falling off. Use scissors to remove extra lengths of dropper and cable tie.
• Suck water into the dropper. Adjust the amount of water so that the dropper floats on the water surface with a 2-3 mm protrusion above the surface.
• Select a plastic bottle with a round cross-section; fill the bottle with water. Put the Cartesian diver into the water and put the top on the bottle.
• The Cartesian diver will sink when you squeeze the bottle tight and will surface when you release it.
• Applying pressure causes the air in the dropper to be compressed and decreases buoyancy, and thereby the Cartesian diver sinks. But when you release the squeeze, the air expands, buoyancy increases, and thus the Cartesian diver floats.

[Tip]	You can also use bubble wrap or a soy sauce dispenser as the Cartesian diver, but a dropper is most suitable due to its good sensitivity and its ease in adjusting buoyancy.
[Keywords]	pressure, buoyancy, Archimedes’ principle
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Koudansha Blue Backs, pp. 42-47