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Drag Coefficient out by a factor of 10, can anyone help?

  1. Mar 1, 2009 #1
    Drag Coefficient out by a factor of 10, can anyone help??

    Im doing an experiment on the drag of a sphere and am trying to work out the drag coefficient. From looking at data online this should be around 0.5 (its a smooth sphere). Using a wind tunnel I measured the drag for various sizes of spheres and wind speeds. An example of one of my results is

    Drag - 0.68N
    Wind Speed - 7.8m/s
    Radius of Sphere - 0.0371m

    Then, using the formula

    Drag Coefficent = (2 x Drag) / Area x Wind Speed^2 x Density of Air

    Having measured the room temperature to be 22 degrees celcius I took the density of air to be 1.204kg/m^3 and the projected frontal area was calculated using pi x r^2

    But this equals 5.039!!!! so could anyone point out where im going wrong?? Im 90% sure all of my values are correct. Thanks in advance for any help :)
     
  2. jcsd
  3. Mar 2, 2009 #2
    Re: Drag Coefficient out by a factor of 10, can anyone help??

    Are you absolutely sure about the calculated drag force? Your equation is correct, although I get 4.293 when I plug your data into it (probably rounding differences). I'm not terribly familiar with wind tunnels, but try checking the units of the readings that you're getting from it.
     
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