1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Speed of Sound and Density

  1. Oct 4, 2014 #1
    So the speed of sound is dependent upon two properties:

    1) Elasticity of the Medium
    2) Density of the Medium.

    Greater elasticity results in a greater restoring force once the molecules are displaced (similar to a spring) so they return to their original positions sooner meaning they can participate in another compression sooner as well, thus increasing the speed of propagation.

    Greater density decreases the speed of sound. The metaphor I'v been using is that, the greater the density the greater the mass per unit volume, so like a spring with a greater mass attached, it will restore/return to its original position more slowly than a material with a lower density.

    So we know that:

    Vsolids > Vliquids > Gas.

    The comparitive densities of the 3 are as follows:

    pSolid > pLiquids > pGas

    However solids are more elastic than liquids which are thus more elastic than gas.

    So in this case, the elasticity trumps the density. (right? Becuase otherwise it just doens't make sense).

    For gases, we have the unique case where the speed is directly proportional to temperature and inversely proportional to Molar Mass and Density.

    My question is, how does density decrease the speed of sound? (is it as i stated above?)

    And in gases, what happens when you increase the temperature at constant volume? Or increase the pressure at constant volume?

    Increaseing pressure via increased temperature would not affect density so however you look at it it looks to increase the speed of sound.

    Increasing pressure by adding more gas molecules or decreasing volume would increase density. What would happen here?

    And finally, if you increased the temperature of solid or liquid, would the speed still increase? isnt that breaking the intermolecualr bonds that contribute to its elasticity?
  2. jcsd
  3. Oct 4, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook