--- Walter Knapp <> wrote:
> > 5. Why does a dish amplify a freqency at 1/8 wavelength?
>
> I think the problem here is a error in thinking about sound waves.
> Sound
> waves in air are not transverse, but longitudinal. And they are the
> movement of particles that have mass. Working from a longitudinal
> waveform with such particles, a reflecting surface down even to
> molecular size will reflect some sound. We cut off what we call
> amplification when the effect the dish produces becomes too small for
> easy measurement. It's a arbitrary point.
I agree.
With sound waves, it is the movement of compression and rarefaction of
air molecules that are longitudinal waves.=20
I say this so that someone doesn't confuse what Walt said to think that
air molecules are moving from the sound source to the ear or mic. They
are not. The air molecules move to a degree longitudinally
(compressing the air in direction the sound is moving), and then the
air molecules move backwards (rarefaction) in a cyclic fashion. The
compression wave travels through the medium, but the air molecules
themselves do not travel the distance.
bret
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