[Phys-L] Re: thrown ball with air drag

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

> I think Michael has the correct analogy. The resistive force, R,
> can be written as b*v^2  in this case. Rewrite the final result
> as
>
> 1/(b*v^2) = 1/(b*vo^2) + 1/(b*vt^2)  and this becomes
>
> 1/R  = 1/Ro + 1/Rt
>
> which is an exact analogy to parallel resistors.
>
> Bob at PC


Yeah; it's easy.

I actually derived the result a little differently, though.  First I
said to myself, "Gee, you know, that final squared velocity looks
JUST like a focal length."  Then I realized that the initial velocity
squared was even MORE like an object distance.  Looking around for an
image distance, the only thing that made any sense was the square of
the terminal velocity.

Thus, applying the thin lens formula, I obtained.

1/v^2 = 1/vo^2 + 1/vt^2

Imagine my surprise that it worked out so well and so easily!

(And David tried to make it SOOOO hard.)
--
John "Slo" Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>
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