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[Phys-L] Re: Sound



This means the air near the earth radiates (loses internal energy) more
than the air above it, or the earth radiates more than the atmosphere
and cools the air just above it by conduction, or both or either, and
the cooler (denser) air sinks?

Is there fog nowadays in Iraq?

bc, what?

Steven M. Gollmer wrote:
This is more than a subjective perception. At night radiative cooling results in a cooler layer of air near the earth's surface. If the winds are relatively calm, there will not be much mixing between the surface air and the air aloft. A sound source in the surface layer will spread out in the shape of a hemisphere. However, due to the differences in temperature and density between the surface air and the air aloft some of the sound will refract back towards the surface resulting in an increased sound intensity. During the day the effect is just the opposite. The sun warms the surface layer and the sound refracts away from the surface reducing the sound intensity. This effect also explains why a train whistle sounds louder on a cold morning.

Steve Gollmer
Cedarville University



kowalskil@MAIL.MONTCLAIR.EDU 07/15/05 1:59 PM >>>

I suspect that subjectively evaluated loudness depends on how noisy the
environment is. And I guess that the difference between the day and
nigh is minimal when one is very close to the source of sound;
everything else being identical.

Ludwik Kowalski
Let the perfect not be the enemy of the good.


On Friday, Jul 15, 2005, at 13:41 America/New_York, Jim Green wrote:


My son, who is sometimes bored out of his skull in Iraq, asks the
following:

At 10:22 15 07 2005 , the following was received:


Mortars sound louder at night here. Why?

Comments???


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