**Date:** Tue, 30 Apr 2002 10:02:51 -0400

**Author:** "Jason St. John"

**Subject:** Re: "sound advice"

**Post:**

Could it be that the Doppler effect gives different perceived frequencies

in the two cases because of the difference between observing/listening

while at rest with respect to the sound-carrying medium and

observing/listening while moving through the air?

-St.John

Boston University

On Tue, 30 Apr 2002, Anthony Lapinski wrote:

> I have 2 questions about sound:

>

> 1) Doppler effect equation for source/observer moving toward the other is

>

> fo = fs[(343+vo)/(343 - vs)]

>

> Similar equation if they recede.

>

> An alarm sounds. If the observer recedes, you hear a frequency. If the

> source recedes, you hear a slightly different frequency. The Doppler

> frequencies are NOT symmetrical around the alarm frequency. This can be

> seen mathematically in the equations, but is there a CONCEPTUAL

> explanation?

>

>

> 2) The speed of sound does NOT depend on its frequency. If wind is

> blowing, the wavelength changes with the speed, keeping the frequency

> constant. The same is true for refraction, like a wave going from air to

> water. But what about the temperature of the air? If the air warms up,

> speed of sound increases. Won't that INCREASE the pitch (like for the wind

> instruments), keeping wavelength constant? I know the length of the tube

> also increases, but the speed change for air is more of a factor. Am I

> missing something here is this last situation?

>