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Homework Help: Capillary rise-conceptual

  1. Dec 23, 2009 #1
    1. The problem statement, all variables and given/known data

    A capillary is dipped in water vessel kept on a freely falling lift, then

    a)water will not rise in the tube
    b)water will rise to the maximum possible height of the tube

    2. Relevant equations

    W=2[tex]\pi[/tex]r S cos[tex]\theta[/tex]
    or h=(2S cos [tex]\theta[/tex])/(r[tex]\rho[/tex]g)

    3. The attempt at a solution

    as this is the case of free fall g tends to 0 hence h tends to infinity hence the option (b)

    but it might also mean that cos [tex]\theta[/tex]=0, i.e, the water doesn't rise at all, hence the option (a)

    which logic is correct?
  2. jcsd
  3. Dec 24, 2009 #2
    Just an educated guess here, as no one else is around--but the way I see it the tendency to minimize surface area and hence form some angle theta is a function of surface tension which is independent of weight. The capillarity (attraction to the glass and consequent pull up the side is also present. OTOH, what happens to the weight of the water as it free falls?
    Last edited: Dec 24, 2009
  4. Dec 24, 2009 #3
    I'm guessing here too, but I'd imagine it'd rise to the top of the tube, as the molecular forces responsible for the surface tension are still present, but the water has no effective weight as the lift is in free fall, therefore there will be a net upward force which will pull the water up the tube.
  5. Dec 24, 2009 #4


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    Homework Helper

    And on outer surface as well, I think
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