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Surface tension doubt

  1. Dec 9, 2014 #1
    If I have a U-shape wire frame and it contains a straight sliding wire and I dip this in soap, a film forms between the sliding wire and the boundary of U shape frame. Why is the force due to surface tension F = 2Tl where l is length of sliding wire?

    They say there are 2 layers in contact. Which 2? There is only one film.

    Also
    ##dW=Fdx=(2Tl)dx##
    They book says 2ldx is the change in area dA. Why?
    ##dW = Tdx##
    ## hence, T= dW/dA##
     
    Last edited by a moderator: Dec 9, 2014
  2. jcsd
  3. Dec 9, 2014 #2

    Bystander

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    How many sides does the film have?
     
  4. Dec 9, 2014 #3
    4 sides. 1 stuck withe the slider. 3 bounded by frame.
     
  5. Dec 9, 2014 #4

    Bystander

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    Not edges --- sides?
     
  6. Dec 9, 2014 #5
    The film has two surfaces. There is surface tension on each surface.

    Chet
     
  7. Dec 9, 2014 #6
    Understood. 2 surfaces.
    Thank you
     
  8. Dec 10, 2014 #7
    exper2_04.jpg T
    One surface and then flipping this vertically
    upload_2014-12-11_10-6-36.png
    in this way two surfaces.Each surface has surface tension so F = 2Tl.
     
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