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Excess pressure on the concave side of the meniscus

  1. Feb 9, 2015 #1
    Why is there excess pressure always on the concave side or surface of the meniscus?

    In my book it is also written that excess pressure balance the vertical resultant forces due to surface tension.
    How can a pressure balance a force?

    My teacher said that shape of meniscus does not depend on vertical component of force.
    Which force is she talking about? Why doesn't the shape of meniscus does not depend on vertical force as there are also curved meniscus so shouldn't vertical force should have some role to play in the curved surface?
  2. jcsd
  3. Feb 9, 2015 #2
    There are two forces involved in capillary action which dictate the curvature of the meniscus.
    1. The adhesion of the molecules to the surface of the container - so water adheres to glass which drags the sides of the meniscus upwards
    2. The cohesion of water which glues the surface of the water together as in raindrops.
    So the shape of the meniscus is the balance, basically, of these two forces.

    Naturally if a tube is thin the grip on the sides of the tube pulling the water upwards overcomes the force caused by gravity and pulls the water upwards. There are a few models for this but interestingly none of them exactly predict experimental results.

    There a few complexities which I have left out for the sake of brevity.
  4. Feb 9, 2015 #3
    What about the shape of meniscus?
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