For the equation F=Cd*A*density of air *V^2,
I think this only shows the pressure different force.
According to my study on wind speed measurement in these days,
I think the friction force is not included in that formula.
(This is only my thought)
From the aerodynamic point, the difference of pressure produces
two force: one is the trag force,the other is the lift force.
Changing the shape of the car body, can change the fluid field,
then change the trag force.
The trag coefficient is mainly depending on Renault number.

I don't and can't go into very detail,:)

Maybe I should ask fireleaf about it...

to be continued...
【 在 mika (New World, Take Time) 的大作中提到: 】
: According to my memory.
: The air drag force is mainly determined by two kind of force.
: One force is the friction force, which is generated by the friction between air molecule and the surface of the car body.
: ...................
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FROM 134.130.181.*