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Will it float or will it crunch?

  1. Feb 25, 2017 #1
    An oil drum will crunch if all matter is taken out. If you empty an oil drum at the edge of space, ceal it, and release it (without kinetic energy so no escape velocity), wil it float somewhere in the atmosphere? Or will it crunch and fall on the earth? Is it possible to create a stucture strong enough and light enough that when all trapped air is sucked out, will start to float instead of crunch?
  2. jcsd
  3. Feb 25, 2017 #2


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    Welcome to PF.

    The density of air at 15°C and Sea Level is 1.225 kg/m2.
    An oil drum has a volume of 200 litres, so to float it would have to weigh less than 1.225 * ( 200 / 1000 ) = 245 gram.
    It is unlikely that you could make a drum that would float without crushing. It is far more probable that an empty container that floats in air would be a sphere.

    A soap bubble has tension in the membrane so it is stable. Compression in the surface of a very thin shell will result in buckling and collapse if any asymmetric forces are applied.

    To build a vacuum balloon you will need to fabricate a spherical support from a space frame having thickness, such as an octet truss. Then collapse the external membrane onto that support. The outer cover should not be in tension until the balloon is evacuated as that would subject the truss to an unnecessary compressive force. That will require two quite different materials for the truss and the skin.

  4. Mar 3, 2017 #3


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    Not quite what you asked about but perhaps of interest..

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