Drag Coefficient vs Air Velocity

(Created prior to 1993)

Question:  When you measure drag coefficient, you must obtain dynamic 
pressure (cm of Hg or water)or g/cm^2.  Will the dynamic pressure change if 
you change the speed.  What is the rate of change of dynamic pressure with 
respects to air velocity (dp/dv)?
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Well, I am not sure I know exactly what you are asking.  The 
frictional force (which gives a pressure if it is divided by area) caused by 
air on a moving body has several sources, and its dependenceon speed varies 
with the geometry of the body, due to turbulence.  I think it is usually 
assumed, for simplicity maybe, that the friction goes as the square of the 
speed, but that may not generally be valid.  Somebody who knows more fluid 
mechanics or aerodynamics should answer this.

Arthur Smith
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