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Homework Help: Calculating air resistance on air

  1. May 21, 2010 #1


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    Fluid Dynamics - Calculating air resistance on air

    1. The problem statement, all variables and given/known data

    I'm trying to figure out how much the velocity of wind will decrease by over a given distance. I know the velocity at a point 1cm after it has passed over an object, and i need to determine the velocity at the object. The flow is turbulent and the object is oscillating.

    2. Relevant equations

    I know the formula for air resistance is F=1/2"rho"v^2*C*L^2, where rho is the density, v is the relative velocity, c is the coefficient of drag and L is the length.

    3. The attempt at a solution

    I have no idea what to do when the question concerns air resistance acting on air. I do not know how to treat length in the equation, as I don't understand how air can have a length. I also do not understand how to find the coefficient of drag on air.
    Last edited: May 22, 2010
  2. jcsd
  3. May 21, 2010 #2


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    Homework Helper

    I don't think that equation applies. As far as I know it's only relevant for solid objects moving through air (by the way, in the general form it's F = ρCAv^2/2, where A is cross-sectional area presented to the air).

    What you're trying to calculate is like a fluid dynamics problem, and although I'm not familiar with much fluid dynamics myself, it seems fairly complex. Maybe someone else will know of a relevant equation.
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