Re: science myth

[brian whatcott <inet@INTELLISYS.NET>]

> On Fri, 27 Apr 2001, Tim O'Donnell wrote:
>
> > I am sure this is a complete science myth.
> > A duck's quack does not echo.
> > How can I verify/falsify this without getting a duck?


At 16:20 4/27/01 -0700, John Mallinckrodt responded:

> Probably not.  Can you quack like a duck?  (And if so, do you walk
> like a duck?  Do you LOOK like a duck?)
>
> Then, later on Fri, 27 Apr 2001, Rondo JEFFERY wrote:
>
> > Does sound echo?

John continued:

> Not usually, as far as I can tell.
>
> > Is a quack a sound?
>
> Yes.
>
> > If the answer is yes to both questions,
>
> Dang ...
>
> Come to think of it, I've heard ducks quack but I've never heard a
> quack echo.
>
> John Mallinckrodt      mailto:ajm@csupomona.edu
> Cal Poly Pomona          http://www.csupomona.edu/~ajm


 This sounds like my cue to chime in with more on myths....

For best resolution, it is preferred to use as narrow a pulse as possible
with pulse radars. If the transmitter pulse is long compared with the
transit time, and particularly if the pulse amplitude is not well defined,
it is quite possible that the return ('echo') will not be discriminated
from the transmitter pulse and such returns may be lost.

Then there is the question of absorption and unfavorable reflection. Some
airplanes - like the old delta wing Avro Vulcan - had rounded wings and
smoothly blended fuselage intersections and buried engines. These were
factors bearing on why the Vulcan was difficult to detect at 20 miles or
less on some airfield radars.
 In the case of the duck's emission, the likely targets may well be more
absorptive than reflective - a wind ruffled lake surface, reeds, shelving
shores, and leafy trees.

One might argue that these heavy birds seek waters with long glidepaths
devoid of many acoustic obstructions, but that is taking this meander too
far beyond the plausible: it is notable that ducks can put up an angle of
climb better than most civil jets when the need arises, and can approach at
steep descent angles.

 But perhaps there is something more to make of the radar analogy: a
current (long-shot) theory of how pulsars generate directed radiation
sounds rather like a description of a phased array. These pretty devices
steer a radar beam with no mechanical movement of the beam generator. If
such an array exists on some spherical surface excited by an internal
rotation of a pulsar, then some peculiar directed effects are postulated.

My imagination suggests that this sort of pulsar beam mechanism would be
quadrupole for no very convincing reason, and it's a bipolar rotating beam
that is wanted for the pulsar, I believe.

Does that clear up the duck's quack issue?
If not, there's always the $10 duck call at the sporting goods store...


brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!