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The role of surface tension in capillarity

  1. Jun 9, 2009 #1
    From what I've read, the surface tension pulls upward on the given volume of water and when this surface tension force equals the force of gravity (weight), there is no more vertical movement up the tube.

    Why is it said that the surface tension pulls upward on the mass of water when surface tension refers to the increased horizontal intermolecular attraction of the top surface layer? Why do you not say that the upward force on the volume of water is the adhesive forces from the container material?
     
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  3. Jun 10, 2009 #2

    tiny-tim

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    Hi Shackleford! :smile:

    I think both views are correct …

    a) Surface tension is a force parallel to the liquid surface and pointing towards the solid surface.

    So when the meniscus goes up (as with water in a glass tube), the force is up, but when it goes down (as with mercury in a glass tube), the force is down.

    In other words …
    b) But the reason why the meniscus is up for water on glass is that water adheres to glass

    and so …
    (And see also http://en.wikipedia.org/wiki/Surface_tension#Liquid_in_a_vertical_tube" for a third argument about minimising the surface area of the water. :wink:)
     
    Last edited by a moderator: Apr 24, 2017
  4. Jun 10, 2009 #3

    Andy Resnick

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    I understand the molecular interpretation of surface tension is commonly taught that way, but I'm not convinced it provides any real insight. It's much simpler to see the result in terms of continnum mechanics:

    http://www.agron.iastate.edu/soilphysics/a577cap.html [Broken]
     
    Last edited by a moderator: May 4, 2017
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