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Unread 10-01-2012, 13:30
jzeisel jzeisel is offline
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Re: Ideal Ball Trajectory Spreadsheet

To find the drag you really need to know the surface roughness of the game balls. The reynolds number is VD/v where V is the velocity, D is the diameter of our game balls and v is the kinematic velocity of air at room temperature.

v = 1.12*10^-4 ft^2/s

I estimate the Reynolds number to be 7.4 * 10^5 at 40 ft/s with the 25 inch diameter. It won't change too much from this number no matter the speed.

NASA has some nice curves that could be helpful for estimates, but this may be the best that will be found unless someone does tests or runs simulations in CFD software.

http://www.grc.nasa.gov/WWW/k-12/air...ragsphere.html

The "Rough" curve is obviously what would be used.
 


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