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Re: [Phys-L] Sound waves in space?




On 2013, Mar 23, , at 10:04, John Denker <jsd@av8n.com> wrote:

On 03/23/2013 09:50 AM, Bernard Cleyet wrote:

"In the anacoustic zone above 160 kilometres (99 mi), the density is
so low that molecular interactions are too infrequent to permit the
transmission of sound."

http://en.wikipedia.org/wiki/Thermosphere

That rather depends on the wavelength. The physics here is easy
to understand: Sound is grossly attenuated unless the wavelength
is long compared to the mean-free-path in the medium.


Note that the wikipedia is inconsistent with itself:

"the speed of sound (in the interstellar medium) is about 100 km/s. "
http://en.wikipedia.org/wiki/Heliosphere


If the physics is simple, that makes a one Hz wave length 100 km, which is about the MFP some where I read somewhere (today). Most? quakes' modes are ~ one s. *** and is rather many dB down at 0.1, IIRC. It would be helpful if the sensitivity of that satellite were easily found. Also bc wishes to know how the satellite differentiates acoustical vibration from mass vibration. Perhaps he read the article too quickly.

*** Rather inconvenient, as ill designed buildings very often have that natural oscillatory frequency.


bc suspects quake bracing's frequency shift may be more important than its strengthening and is too lazy to refer to his library of a dozen quake books.


Sound travels far better in the interplanetary medium, which is
far denser than the interstellar medium.
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