Make a 'Cartesian Diver'

Stanley L. Rapaport, MD
JAMA. 1977;237(20):2188. doi:10.1001/jama.1977.03270470024009.
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To the Editor.—  A simple, endlessly amusing toy called a "cartesian diver," which can be rapidly (2 minutes) and cheaply (no cost at all) made, exquisitely illustrates some fundamental physical principles—resulting in admiration from one's own or others' smaller children with a disproportionate increase in self-esteem.This toy is made from any clear, empty plastic bottle like those used for shampoo or mouth wash and from what to us in medicine is commonplace and worthless, an empty ampule medicine vial.The plastic bottle is filled to overflowing with water. The empty ampule vial is filled about two-thirds full of water so that it just barely floats. The vial is then inverted and placed with the open end down in the filled plastic bottle. The bottle is sealed, and the toy is complete.The action of the toy occurs when the bottle is squeezed from front to back. When this is


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