What is the fastest substance for sound to travel in?

[alexandrae]

**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!

 

[mgb_phys]

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

 

[jobyts]

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?

 

[cragar]

would sound travel faster in an Einstein-Bose condensate.

 

[f95toli]

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.

 

[alexandrae]

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?

 

[mgb_phys]

The equation is good for any uniform substance
Just look up the Youngs modulus http://en.wikipedia.org/wiki/Young's_modulus (approximate values)
Poisson ratio http://en.wikipedia.org/wiki/Poisson's_ratio (Poisson's ratio values for different materials)
And density - then plug them into the equation, make sure the units match.

 

[Redbelly98]

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.

 

[nshtkmar1977]

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.

 

[jobyts]

Does the frequency of the sound matter?

 

[Redbelly98]

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/