CARTESIAN DIVER
hydrostatics
Description of the device
Classic physics experiment named after Descartes – it demonstrates the Archimedes’ law of buoyancy through presentation of principle of floating and sinking, Pascal’s law and much higher compressibility of gases than fluids.
Phenomenon
The diver is affected by two forces: gravity pointing down and buoyancy pointing up. Net force or difference of those two forces, determines the direction of the diver’s motion. If the diver’s average density is lower than the density of the liquid, the buoyancy predominates keeping the diver in the upper position (Archimedes’ principle). Pushing the lever increases pressure in the whole vessel (Pascal’s law), which causes air compression in the diver and allows pouring more water inside the diver, therefore making it heavier.
How to use it
Push the lever and observe what happens to the diver, which is filled partly with liquid and partly with air. Try changing the amount of force applied to the lever. Notice how the air volume in the diver changes. Try to immobilize the diver halfway up the height of the vessel.