This is the idealization of a common toy, the Cartesian diver. It demonstrates Archimedes' Principle as well as the ideal gas law.
You have an external glass container filled with a liquid (blue). You can exert pressure on the liquid by pushing (via mouse-drag) on the plane on top of the spring.
In the liquid is an inner container, in which air is trapped (white). By pressing on the plate with the spring and increasing the pressure, the liquid is not compressed, but the trapped air is. Consequently the displaced volume of liquid changes, and the diver can be made to rise or sink.
Through variation of the spring force, you can achieve that the diver floats at a certain height. We have drawn in a yellow line, and you may want to attempt to have the diver float right at the yellow line.
If you are feeling competitive urges, we have also included a stop watch with which you can measure how long it take for you to get the diver to float right at the yellow line. The stop watch display the time in milliseconds and is automatically stopped when you reach the desired goal. Just press the "s" key to start the stop watch. Have fun.
© W. Bauer, 1999