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Forces inside of a capillair

  1. Feb 26, 2009 #1
    Hello,
    recently i was thinking of a capillair and what would be the pressure on the top of the liquid in the capillair.I was predicting something like this to happen:
    -capillair will rise water to the height x above the water surface in the glass of water
    -if i will apply some underpressure(under atmospheric) at the top of the capillair, then the water will rise additional height y above the x(so total water level in capillair x+y above the surface in glass of water).
    -if the same underpressure would be applied to noncapillair tube, it would also rise water to height y.

    My thought was that water inside of the capillair is in stational conditions(all forces are adding to zero,so water does not move anymore in any direction).However I got surprised when i made following experiment:
    I placed a capillair and parallel to it a much wider pipe to compare the height of risen water.Both pipes were connected with a t-junction.Initially i let the water to rise in the capillair.Water in the wider pipe have not risen.Then i sucked some air out of the pipe system to create underpressure,but water in capillair has not rised any higher than in wider tube!
    I got perplexed..if water in the glass is in equilibrum and if water in the capillair too...then why is equally applied underpressure not rising water to the same relative height(relative to the original level be it capillair water surface top or glass of water sufrace).


    Any help would be much appreciated :) and no,it is not homework or any assignment :D just a part of my design for a capillair pump.
     
  2. jcsd
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