Re: pinhole RE: Speed of sound

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Thu Apr 08 2004 - 11:50:06 PDT 

Message-Id: <l0311071abc9b4b8e80db@[192.168.112.30]>
Date: Thu, 8 Apr 2004 11:50:06 -0700
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole RE: Speed of sound

Hi Sherry

It's more complicated than that.

Sound travels faster in stiffer materials and it travels slower in denser
materials that have the same stiffness.)
Alas stiffness and density are often coupled.

actually the speed is proportional to the square root of the quantity
(stiffness divided by the density)

water is 800 times denser than air (so sound should travel slower) but
water is
20,000 times stiffer so sound actually travels faster in water.

For air stiffness is proportional to the air pressure, so is density,
however temperature also controls density and stiffness, density is
independent of temperature (in a constant volume container in which you
don't allow the amount of stuff to change) but stiffness or pressure is
proportional to temperature (even at constant volume and stuff) So for air
the speed of sound is proportional to the square root of temperature. (For
air the speed of sound is pproportional too the square root of the quantity
(pressure divided by density)

Paul D

>My class is studying sound. We understand that sound travels faster in
>more dense matter. If that is true, why does sound travel faster in warm
>(25 degrees C) air than cold (0 degrees C) air. As the air warms, it
>expands and becomes less dense, yet the sources I find report that sound
>travels faster in the warm air.
>
>Is this a book error, or is it a "little more complicated than that?"
>
>Sherry Anderson
>
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