Francois Labreque wrote:
> 
> Well, a few years ago, some english chap name Newton came up with the
> silly idea that a force apllied to an object resulted in a acceleration
> proportional to its mass, of f=ma for short.
> 
> the force caused by air resistence is computed by the following formula:
> 
> F = (Cd)A(V^2) in the direction opposing the movement.
> 
> Where:
> - Cd is the drag coefficient ( 1 for a box, 0.5 for a sphere and around
> 0.30 for most modern cars)
> - A is the cross-sectional area of the object (area "facing" the air
> flow)
> - V is the speed of the object in that direction.
> 
> Provided that the shape and mass of your object dont change, you can see
> that the force, hence the decelleration, will decrease at a rate which
> is proportional to the square of the current speed.
> 

You should mention, that Cd is in fact not a constant but is a highly
complicated function of the reynolds number and thereby also depends on
the speed.  Values given for cars etc. are usually only valid for a
limited range of speed.  

BTW with some shapes (like the wings of a plane) it is even more
difficult, because the force no more only goes in direction opposite to
the air flow.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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