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The reynolds number equation, need help.

  1. Jun 15, 2007 #1
    I understand most of the equation.

    [tex] Re=\rho *D *V
    over a symbol I don't recognize

    I don't know what the symbol is the denominator, and I can't find its name so I don't know what it means. I just need one definition, thanks.
    Last edited: Jun 15, 2007
  2. jcsd
  3. Jun 15, 2007 #2


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  4. Jun 15, 2007 #3
    Its the viscosity, mu.
  5. Jun 15, 2007 #4
    I was given the above equation in order to find drag coefficient through estimation and Reynolds Number. Where would I find a Reynolds Number - Cd Chart?
  6. Jun 15, 2007 #5
    I'm having a problem with another related problem. If I wanted to find terminal velocity, the Cd=1.17, the Ac=.4522 m^2 and the weight equalled 5.67 grams or.0556037055 newtons and the air density is 1.184 with no turbulance, what do you get? I think the problem may be my arithmetic.
    In the terminal velocity equation, I get .33347775 over .7914693. I know this isn't right. What am I doing wrong?
  7. Jun 15, 2007 #6


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    Interesting... Since you apparently know when you have the wrong answer, how about you just go through and eliminate every answer that you know is not right until you only have only one answer left over. That answer, by process of elimination, must be the right one.

    This method of solution may be applied to all of your homework problems without fail.
  8. Jun 16, 2007 #7


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    First off, if you are still talking about a quarter, the area you are using is way off. The measured diameter of a quarter is about 24 mm. Therefore the area is

    [tex]A =\frac{1}{2}*\pi*(24 x 10^{-3} m)^2[/tex]

    [tex]A = 4.52 x 10^{-4}[/tex] [tex]m^2[/tex] or [tex]A = .000452[/tex] [tex]m^2[/tex]

    The variable that you are asking about, [tex]\mu[/tex] is the dynamic viscosity of the medium the object is moving in, i.e. air. In that example, the seal level value for [tex]\mu = 1.79 x 10^{-5}[/tex] [tex]\frac{N*s}{m^2}[/tex]

    Reynolds Number is a unitless number, i.e. all units should cancel out when it is calculated.
    Last edited: Jun 16, 2007
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