AW: AW: Underwater latency (not completely OT) ;-)

["Rainer Thelonius Balthasar Straschill" <rs@moinlabs.de>]

The way sound travels in different phases (solid, liquid, gaseous) is 
actually rather different on a half-macroscopic scale (i.e. while the laws 
how atoms and subatomic particles interact are believed to be the same and 
the equations for speed of sound calculated from density and 
compressibility (or rather its different definitions) look the same, the 
process or how it is explaind differs on the scale "in between".

If you look at the equations on a macroscopic scale, they all look like c 
= SQRT(K/rho) with K a constant (actually a 2nd order tensor, a modulus). 
In the case of gases, K= chi*p with chi the isentropic exponent (a 
constant) and p the pressure. Substituting with the definition of the 
density in gases, rho = p/RT (R the Reynolds number, T the Kelvin 
temperature), we get c=SQRT(chi*R*T), and voilá - the speed of sound in 
air is independent from the pressure. The pitfall? This equation is only 
valid up to a certain amount for the avg. free length of path (don't 
remember how this was defined - I came from the condensed matter area).
Thinking about it, I don't see the logical explanation that sound travels 
faster in water than in air. There are different mechanisms involved. And 
if we'd breathe argon and bathe in quicksilver, things would be different 
;).

Elasticity is not the same as compressibility. The short explanation: 
elasticity describes changes if you apply force in one direction (like 
pulling on a string), while compressibility is if you push from all sides 
simultaneously.

        Rainer

-----Ursprüngliche Nachricht-----
Von: Doug Cox [mailto:dougcox@pdq.net] 
Gesendet: Dienstag, 15. März 2005 22:17
An: Loopers-Delight@loopers-delight.com
Betreff: Re: AW: Underwater latency (not completely OT) ;-)


This can be found here: http://hypertextbook.com/facts/2000/NickyDu.shtml

Sound is a type of longitudinal, mechanical wave. They need a medium to 
propagate and will not travel through a vacuum. Sound travels at 
different speed in different media. The speed of sound is determined by 
the density and compressibility of the medium. Density is the amount of 
material in a given volume, and compressibility is the how compacted 
could a substance become for a given pressure. The denser and the lower 
the compressibility, the slower the sound waves would travel. Therefore, 
the speed of sound is about four times faster in water than in air. The 
speed of sound can also be affected by temperature. Sound waves tend to 
travel faster at higher temperatures. I have found different values for 
the speed of sound in water in different sources. They range from 1450 
to 1498 meters per second (m/s) in distilled water and 1531 m/s in sea 
water at room temperatures (20 to 25 °C).

The speed of sound in a medium can be determined by the equation...

/v/ = (/B//ρ)^1/2

Where...

    /v/ is the speed of sound,
    /B/ is the bulk modulus of elasticity, and
    ρ (rho) is the density.

The bulk modulus of elasticity, also known as the compressibility, is 
the relationship between pressure and volume. It is a measure of how 
much an increase in pressure would decrease the volume.

Nicky Du -- 2000



Jesse Lucas wrote:

> Rainer Thelonius Balthasar Straschill wrote:
>
>> If I remember my (very) basic university classes in physics, we 
>> usually would test any theories we might have by bringing them to 
>> extreme values and see what happens. If lower density = lower speed 
>> of sound, then we would have sound travelling at infinite speed in 
>> vacuum. I don't believe this is the case.
>
>
> In space there is no medium for sound to travel through. See the tag
> line to the film "Alien."
>
>
>
>
>