The Cartesian diver

Physics of the Mundane

Adam Johnston

In a class demonstration, an eyedropper (also referred to as the Adiver@) inside a sealed plastic bottle of water is commanded to rise and fall via the voice and telepathic commands of the amazing instructor.  This feat has required years of training in physics, and should inspire some amount of awe.

You should:

1.              Replicate this feat.  Use your own plastic bottle (a 1 or 2 liter beverage bottle), an eyedropper and some water. You can also use an additional container of water to train your diver. (If your diver is not properly “trained,” it will not respond to you; but, instead either sink like a rock or float like a cork.)  Determine the necessary conditions that allow you to control the diver to either rise or sink.

2.              Explain how this works.  Specifically pay attention to what is happening to the eyedropper, why these things happen and how these are related to the sinking or falling condition of the diver.

Other questions to pursue:

3.              How does one’s control of the diver change if the bottle is only half full?  Why does this matter?

4.              Why must you keep the cap on the bottle?

5.              Why must you train your diver before you can command it properly?  How does a properly trained diver compare to the gel spheres within Orbitz?  Why would a diver need to be re-trained if it were diving in a different substance?

6.              Could the diver be commanded to rise and fall if it did not have a hole in the bottom?  (Try it and find out!)