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Name: Nevnariel A
Status: student
Age: 15
Location: N/A
Country: N/A
Date: 7/21/2004


Question:
Dear Sir/Madam, Why is it that as sound waves pass from a deeper region to a shallower region of water, their speed decreases?


Replies:
The speed of sound in water depends upon several factors: depth, temperature, pressure: At first the speed of sound decreases with depth (decrease in water temperature), but at about 1000 m it begins to increase with depth because the temperature becomes more or less constant but the pressure increases. As a result at about 1000 m the speed of sound becomes a minimum. This creates a "megaphone" effect where sound can travel for thousands of kilometers. See:

http://www.oceansatlas.org/unatlas/about/physicalandchemicalproperties/back ground/seemore2.html

Vince Calder


Dear Nevnariel,

The speed of sound is dependent on the density of the medium -- and, in general, sound waves travel faster through mediums that are more dense. See for example, this web site, which lists the speed of sound for a variety of materials:

http://www.uk-piano.org/sound.html

The deeper regions of water would be at a higher pressure (and therefore more dense), so you would expect the speed of sound waves to be higher. Here is a web site that explains some of the equations used to calculate the speed of sound in seawater at various temperatures, salinities, and pressures:

http://www.npl.co.uk/acoustics/techguides/soundseawater/content.html#UNESCO

Regards,

Todd Clark, Office of Science
U.S. Department of Energy



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