# Density and sound velocity

1. Aug 9, 2013

### B4ssHunter

does density affect sound velocity ?
i know sound velocity is dependent on inertial and elastic properties
but does it depend on density ?
or just molecular mass ?
if two objects having the same atomic mass , but one has higher density than the other due to the difference in bonding
wouldn't velocity of sound be greater in the one with higher density ?
i understand that velocity of sound decreases in larger atoms , because they have more mass, but wouldn't that be accompanied by larger volume causing their density to actually decrease ?

2. Aug 9, 2013

### davenn

hi there :)

yes it does, for a couple of examples.... in water the speed of sound is ~ 4 times faster than in air and
in iron its ~ 15 times faster than in air.
Sound is a compression wave so in in any given medium there are 3 factors that affect the propagation speed ...
1) compressibility... 2) shear modulus and 3) density

edit: ... I should really mention that temperature also plays a part
cheers
Dave

3. Aug 10, 2013

### B4ssHunter

excuse but i read that actually what makes sound travel faster in iron is the elasticity not the density , i read also that density slows it down

4. Aug 10, 2013

### davenn

its a mixture of the 3 things I mentioned above

yes but the compressibility then plays a big role on the which can make up for the drop in speed as the density increases

have a look at the wiki page for a pretty good description
http://en.wikipedia.org/wiki/Speed_of_sound

Dave

5. Aug 13, 2013

### cjl

Shear modulus does not really affect the speed of sound. Rather, it's pretty much exclusively determined by bulk modulus (compressive modulus) and density. Higher bulk modulus = higher sound speed, higher density = lower sound speed.

6. Aug 13, 2013

### sophiecentaur

c=√(K/ρ)
Where k is bulk modulus and ρ is density in condensed matter
Ain't Maths a great language? An equation is worth a thousand words.