[Leica] why do bombs whistle?

[henningw at archiphoto.com (Henning Wulff)]

>thanks to all.
>
>I figured it was doppler based, but I would think the pitch would
>INCREASE as the bomb falls toward you.
>I am basing this on the increased pitch of car siren coming toward you.
>OR or as a different concept, a standing wave in an organ pipe as you
>shorten it, the pitch increases.
>
>Could the drop in pitch be related to change in air density through
>which the falling object passes?
>
>Comp sci is computer science. But in the 80's we were programming in
>LISP and Pascal..
>So that is worth 3 cents in today's market.
>My dad used to reminisce about programing by punch cards.
>
>Eric
>


If a bomb is descending at its terminal velocity when you start 
hearing it, and it is not aimed dead at you, the pitch will 
(hopefully) decrease to the vectors involved.

Imagine the bomb coming straight down at you (run!!!! :-)), and then 
one coming straight down a couple of hundred yards away. As the one 
further away gets closer to the ground, the vector of the sound 
heading your way decrease in value. What that means is that its speed 
of approach (to you) is decreasing, and just as it hits its speed of 
approach to you is 0. Therefore at the time of impact the doppler 
compression that the sound waves experience is zero, whereas the 
sound of the bomb that is heading right at you does not change its 
rate of approach to you, and you will hear the same pitch until 
impact.


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    *            Henning J. Wulff
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