Cartesian Diver that Floats When Squeezed

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What kind of experiment is this?

Experimental procedure and explanation:

• A typical Cartesian diver sinks when the plastic bottle in which the diver is immersed  is squeezed and floats when the force is released. Squeezing the bottle decreases its volume. This compresses the air inside, which reduces buoyancy and thus causes the diver to sink.
• If a plastic bottle with an oval cross section is used, the diver floats when the bottle is squeezed and sinks when the pressure is released. This is opposite to the behavior of a typical Cartesian diver. This is because the volume of a bottle with an oval cross section increases when the bottle is squeezed.

[Keywords]	Buoyancy, Archimedes’ principle
[Related items]	Cartesian Diver
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs pp. 42–47.