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)?

Replies:
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.

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