Re: Air resistance

[brian whatcott <inet@intellisys.net>]

At 12:23 12/13/97 -0800, you wrote:

> > The data are not as good as we would like them to be but how can they be
> > so bad?
>
> Just to reiterate, the data are not at *all* bad.  But the fact remains
> that they don't *begin* to be sufficient to determine "n"  with any
> precision. This is primarily because the data are taken over far too
> limited a range of velocities. 
> ....
> A. John Mallinckrodt

I am rather more critical - I assert that no matter how far the data 
acquisition is extended, you will not determine "n" with any precision
using the present method, because it is not expressible as a constant
with this method.
You gain one CERTAIN datum - the resistance at terminal speed.

The current method makes an unwarranted assumption as to the 
shape of the resistance curve - that it involves some constant power 
law; and it has previously been noted that you cannot rely on this.

 I think it may have been John who previously noted that fluid dynamics 
is a complex topic. If you take the aeronautical approach of expecting 
drag to grow as V squared, you need to provide a variable coefficient 
of drag to account for the complexities of fluid flow variation at 
different speeds, otherwise, the exponent will vary with speed.

  That's why I think the bicycle shop at Dayton did rather better at 
deriving values for drag than you gentlemen - though their 
instrumentation was not superior; they held more experimental variables 
constant and assumed less by their choice of a wind-tunnel as their
experimental tool!

Sincerely
brian whatcott <inet@intellisys.net>
Altus OK