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Conceptual question about syphons

  1. Feb 2, 2008 #1
    Is it physically possible to syphon a liquid from a pool of water back to itself?

    My thoughts: Variables involved are acceleration due to gravity, change in height, surface tension, air pressure, friction, radius inside and vacuums. If you take all the air out of the tube and place both ends below the surface of the liquid, the pressure at the ends, the radius, and the surface tension don't matter. Setting both ends at the same height means there's no acceleration. In this kind of system, it seems to me like all you would have to do is apply a force to get the liquid going, and it would keep flowing forever (disregarding friction) due to the vacuum created.

    idk, though. What do you think?
  2. jcsd
  3. Feb 2, 2008 #2
    You would of course need to disregard friction as you say to get the unphysical result that you desire. Might work for a while with a super fluid. Maybe.
  4. Feb 3, 2008 #3


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    Staff: Mentor

    Yes, lots of things could go around in a circle forever if there were no friction.
  5. Feb 3, 2008 #4


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    Science Advisor
    Gold Member

    It won't work even with a superfluid. The "fountain effect" that is often demonstrated using superfluid helium comes close, but is actually driven by thermal radiation from the environment.
  6. Feb 6, 2008 #5
    I think I see why it wouldn't work. Any low pressure caused by the moving fluid could be filled from either end.
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