Quick Answer: The Cartesian Devil, also called a Cartesian diver, is a small figure in a sealed, water-filled transparent container that sinks when the container is squeezed and rises again when the pressure is released.
Last updated: October 2026
Key Features
Diver figure floats near the surface at rest
Sinks as pressure on the sealed container increases
Rises again when the pressure is released
Shows buoyancy, density and the compressibility of air
Technical Specifications
Specification
Value
Also known as
Cartesian Diver Apparatus
Use
How pressure changes affect floating and sinking
Operation
Manual pressure-based demonstration
Learning concepts
Buoyant force, density, pressure transmission, air compression, floating, sinking, Archimedes’ and Pascal’s principles
About This Product
Squeezing the container raises the pressure in the water, which compresses the air trapped inside the diver, increases its density and makes it sink. Releasing the pressure lets the air expand so the diver rises, a simple way to explain Archimedes’ and Pascal’s principles and how submarines control their buoyancy.
Frequently Asked Questions
Why does the Cartesian Devil sink when the container is squeezed?
The extra pressure compresses the air trapped inside the diver, so its density rises above that of the water and it sinks.
