Does Density Affect Sound Velocity in Condensed Matter?

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Discussion Overview

The discussion centers around the relationship between density and sound velocity in condensed matter. Participants explore whether sound velocity is influenced by density, molecular mass, and other factors such as compressibility and shear modulus.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions if sound velocity depends on density or just molecular mass, suggesting that higher density might lead to greater sound velocity if atomic mass is constant.
  • Another participant provides examples indicating that sound travels faster in denser materials like water and iron compared to air, citing compressibility, shear modulus, and density as factors affecting sound propagation speed.
  • A later reply challenges the idea that density contributes positively to sound speed, arguing that elasticity plays a more significant role and that increased density may actually slow sound down.
  • Some participants mention that compressibility can offset the effects of increased density on sound speed.
  • One participant presents a mathematical expression for sound speed in terms of bulk modulus and density, emphasizing the role of these parameters in condensed matter.

Areas of Agreement / Disagreement

Participants express differing views on the influence of density on sound velocity, with some arguing for its positive effect and others suggesting it may slow sound down. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants reference various factors affecting sound velocity, including compressibility, shear modulus, and temperature, but do not reach a consensus on the relative importance of these factors or their interactions.

B4ssHunter
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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 ?
 
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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
 
davenn said:
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
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
 
its a mixture of the 3 things I mentioned above


i read also that density slows it down

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
 
davenn said:
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

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.
 
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.
 

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