Cartesian diver

[Fu-Kwun Hwang]

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The following are copied from http://lectureonline.cl.msu.edu/~mmp/applist/f/f.htm

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. However, it is an un-stable equilibrium.  Have fun!

And I have created an EJS version of the same simulation.

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[Fu-Kwun Hwang]

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Here is another version with two divers.
You can adjust the system such that one of them is moving down and one of them is moving.
You can also have them both float in the middle.

We have this kind of competition in Taiwan. Each one will play with 8 to 10 divers.
If the hole in the diver is different, the water leak out/in rate from/to the diver is also different.
Press the system slowly or quickly will have different effect on the divers.
Each diver can be controled, moving down or up by your hand. One diver can also rescue another diver.
They are many ways to play with it. I hope you can make one for yourself and enjoy the fun playing with it.

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[lookang]

In order to understand more quickly
Let me explain:

b = coefficient of friction/damping between the blue liquid and the diver
the red arrow is the velocity of the diver
air in trapped inside diver which is inside the bottle
the yellow button allows simulated pressure to be exerted in the liquid in the bottle
the bottom of the diver is open, to allow liquid pressure to force the air trapped in the diver to a smaller volume

the best way to learn is to make the cartesian diver yourself, i made one already.....
i used the "magic" fingers to pretend i can control the diver, the students are amazed and puzzled
It is quite fun for the students!


Found a youtube that shows well the concept and how to construct it
Cartesian diver
This classic experiment is a fun way to explore why things float or sink.

[Fu-Kwun Hwang]

Here are some pictures show you how to make one by/for yourself.