Cartesian Diver

DCS Code: 2B40.30 Last Updated: March 27, 2026
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Purpose

Pressing a neoprene membrane on a sealed water-filled cylinder compresses the air pocket in an inverted test tube diver, increasing its density and causing it to sink. Demonstrates the interplay of Pascal's principle, Archimedes' principle, and Boyle's law.

Side-by-side photos of a tall clear acrylic cylinder filled with water, sealed with a neoprene membrane and band clamp. An inverted test tube with a paper clip chain hangs inside. Left: diver floating near the top with chain extended. Right: a hand presses down on the membrane and the diver has sunk lower.
Figure 1: Left: diver floating at neutral buoyancy with air pocket visible. Right: pressing the membrane compresses the air, increasing the diver's density and causing it to sink.
Equipment
Demo Apparatus