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Negative Drag coefficient

  1. Dec 1, 2015 #1
    Hi,
    I am working on a video capture project in which i am videoing the projectile of a ball that is being thrown in the air and trying to fit it to a curve for the expected trajectory of a projectile with quadratic drag.I am running into the issue that in order for my expected trajectory to fit the actual trajectory of the ball the drag coefficient must be negative. Why is that?
     
  2. jcsd
  3. Dec 1, 2015 #2

    boneh3ad

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    Have you checked that you don't have a sign wrong somewhere else?
     
  4. Dec 1, 2015 #3
    If you show your equation, there is a change that someone may figure out the problem.
    Do you have an analytical solution for the motion with drag?
     
  5. Dec 3, 2015 #4
    I am manipulating the data on an expected drag curve and in order to get my data to fit the curve i had to input a negative drag coefficient
     
  6. Dec 3, 2015 #5
    Into what do you input that drag coefficient? Do you have a formula?
     
  7. Dec 3, 2015 #6

    boneh3ad

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    Right so my question is related to that curve. Clearly that curve comes from some sort of model equation, so have you made sure the signs are correct in that model. A negative drag coefficient in a model where the signs were correct would imply that your projectile is moving faster than what is predicted by freefall. Is that actually the case here?
     
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