PURPOSE: To illustrate dramatically the concept of buoyancy.

DESCRIPTION: A float is at rest in a water vessel suspended by a spring from a fixed point. The vessel is lifted up and released from rest, so that it oscillates vertically on the spring. In the picture above a band around the floater lies between the two bands around the larger vessel when the system is at rest. Q: How will the float move inside the water vessel as t he vessel executes simple harmonic motion? A: Surprisingly, the float will remain at rest in the water vessel as it oscillates. It will even remain at rest when the vessel is stopped suddenly with your hand! As the vessel oscillates, the weight density of both the floater and the water bath vary together, as the acceleration of the vessel varies, so the ratio of their densities remains the same, and they will continue to float with the same geometrical relationship!!


REFERENCES: (PIRA unavailable.) See Demonstration Reference File for further description and discussion of this demonstration. I have been told that this idea was proposed early in the NASA space program as a way to reduce injury to astronauts if a crash were to occur to re-entering space vehicles. If anyone has any information on this I would be interested.

EQUIPMENT: Floater in water vessel hanging from spring on stand.

SETUP TIME: 5 min.

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