113 Reverse Cartesian Diver

 

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With cylindrical bottles, the bottle becomes more pressurized when it is squeezed. With dettol bottles, whether the bottle becomes more or less pressurized depends which sides are being squeezed.

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When the bottle is squeezed on the longer sides, the cross-sectional area becomes smaller (because we are making it more elongated).

 

This causes the water in the bottle to rise and press against the bottle cap, thus increasing the water pressure. The increased water pressure forces more water into the diver. Its weight of the diver overcomes the upthrust. And it sinks! This is the classic cartesian diver.

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However, when the bottle is squeezed on the shorter sides, the cross-sectional area becomes larger (because we are making it more circular).

The water level in the bottle drops, causing the water pressure to decrease. The decreased water pressure draws water out of the diver (pushed out by the air pocket at the top of the diver). The weight of the diver drops below the upthrust, and it floats! This is the reverse cartesian diver.

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• 04 Forces