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A sphere filled with a gas will float in a medium less dense like water. I wonder will that same sphere float if the gas is removed and only a vacuum remains. I suspect that the activity of the gas is the reason for its buoyancy and that the sphere will sink as the gas vacates.
Nope, the sphere floats just because it weighs less than the same volume of water, as Archimedes realized. If you evacuate the sphere, it will actually float just a tiny bit higher (air has some weight), assuming that it doesn't implode from the pressure difference between outside and inside.
(published on 10/22/2007)
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