Speed of sound in substances

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  • #1
**this is not a homework question**

I need to know in which substance does sound travel fastest in. I know that sound travels faster when the medium is denser, therefore solids, however I would like to go more in depth. I've heard that it is iridium or hydrogen solid, but I can't get a definite answer. I was wondering if anybody knew for sure?

much appreciated!
 

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  • #2
mgb_phys
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In solids speed of sound = sqrt ( E / 3*density*( 1-2v) )

E is Young's modulus (the stiffness)
v is Possion ratio (a measure of how much the material expands sideways when you press it)

At a guess the fastest speed of sound would probably be in diamond - it's hard = stiff
 
  • #3
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In solids speed of sound = sqrt ( E / 3*density*( 1-2v) )

E is Young's modulus (the stiffness)
v is Possion ratio (a measure of how much the material expands sideways when you press it)

At a guess the fastest speed of sound would probably be in diamond - it's hard = stiff

Speed of sound should be same as the propagation speed of a mechanical vibration in the medium, right?
 
  • #4
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would sound travel faster in an Einstein-Bose condensate.
 
  • #5
f95toli
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Speed of sound should be same as the propagation speed of a mechanical vibration in the medium, right?

Yes, remember that sound IS just a mechanical vibration (which happens to be in the audible range) so from a physical point of view there is no difference between the two.
 
  • #6
hey I'm in eighth grade, can you give me some examples? How would I use the formulas you gave me to find out the answer? Is it a natural or manmade substance?
 
  • #8
Redbelly98
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At a guess the fastest speed of sound would probably be in diamond - it's hard = stiff

Diamond also has a low density (3.5 g/cc), which helps.
 
  • #9
elasticity increases the speed of sound. so metals will give highest speed of sound in them. not only this the temperature, pressure, density, and molecular wt. also play role.
 
  • #10
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Does the frequency of the sound matter?
 
  • #11
Redbelly98
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Does the frequency of the sound matter?

In the human range of audible sound, no.

However, what I remember from my solid state physics (taken 25-30 years ago), at frequencies where the sound wavelength is comparable to the distance between adjacent atoms the speed of sound does change.

I don't remember at what frequencies this typically happens, or whether the speed of sound becomes faster or slower ... perhaps somebody else knows?

To get a ballpark estimate, figure a speed-of-sound of 5000 m/s in a "typical" solid, and a wavelength of 0.2 nm:

f = v/λ = 5x103 / 2x10-10 Hz ~ 2x1013 Hz​

I.e., at frequencies corresponding to I.R. radiation we'd expect changes in the speed of sound.

FYI, I found this listing for speed of sound in some different materials. Berylium is 12.9 km/s, slightly higher than diamond (12 km/s)
http://hypertextbook.com/physics/waves/sound/ [Broken]
 
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