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Density and sound velocity

  1. Aug 9, 2013 #1
    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. jcsd
  3. Aug 9, 2013 #2

    davenn

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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
     
  4. Aug 10, 2013 #3
    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
     
  5. Aug 10, 2013 #4

    davenn

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    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
     
  6. Aug 13, 2013 #5

    cjl

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    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.
     
  7. Aug 13, 2013 #6

    sophiecentaur

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    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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