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Buoyancy in Microgravity

  1. Aug 11, 2006 #1

    Jorrie

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    Take long lab cylinder filled with water. Into the water, drop many little lead balls and also many little plastic balls that are much less dense than water. Seal the cylinder and send it to the ISS onboard the coming Atlantis shuttle flight.

    In the near weightlessness of the ISS, shake the cylinder to spread the balls more or less evenly over the length of the cylinder. Then mount the cylinder vertically (relative to Earth), with its center on the station’s center of mass. Assume that the ISS keeps the same side pointing to Earth and that for a fair period there are no station movements due to positioning thrusters, astronaut movements, space-walks etc...

    Where in the cylinder will the lead and the plastic balls respectively settle?
     
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  3. Aug 12, 2006 #2

    CarlB

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    Ignoring surface effects (for example, coat all the balls in some hydrophillic substance I suppose), the jar separates out into layers. The heavier balls end up at the top and bottom of the jar, the light balls end up in a layer in the middle. The cause of the effect is that stuff farther away from the earth is rotating too fast and stuff closer to the earth is rotating too slow for perfect free fall. Hence, there is a bit of left over gravitational force. What do they call it, tidal force?

    Carl
     
  4. Aug 12, 2006 #3

    Jorrie

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    Thanks Carl, I agree. The reason I put water in the jar is to also show the buoyancy effect. Even it there were no lead balls in the jar, the plastic balls will tend to the point of lowest pressure, which is in the center, due to tidal gravity.
     
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