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Sound and Temperture

  1. Jan 3, 2010 #1

    Wax

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    I was wondering how temperature can affect sound? I'm assuming the hotter the temperature then the louder the sound? Is this correct? Does anyone have a link that I could read more on this subject?
     
  2. jcsd
  3. Jan 3, 2010 #2

    Danger

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    In general terms, you have that backward. Colder, and therefore denser, air transmits sound more effectively than hotter air.
    If, on the other hand, you refer to a higher temperature, and thus more engergetic, explosion that initiates the sound wave, then you are correct.
     
  4. Jan 3, 2010 #3
    If you mean transmission of sound in gases, then it's also worth pointing out that sound travels faster with increasing temperature (other things being constant). It's proportional to the square root of the temperature in kelvin.
     
  5. Jan 3, 2010 #4

    Wax

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    Interesting, why is there a difference? So if I drop a brick then it would be louder in cooler temperatures? On the other hand, if I light firecrackers then the sound would be louder in warmer temperatures?
     
  6. Jan 3, 2010 #5

    Danger

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    Not quite. Sound travels more 'energetically' in a dense medium, which is why you hear better under water. You will hear any sound louder in colder air.
    My reference to temperature of an explosion referred simply to the fact a higher temperature of conflagration results in a more energetic pressure wave.
     
  7. Jan 3, 2010 #6
    For sound speed in gases you have to take more than just density into account. The definition of sound speed is

    [tex]c = \sqrt{\left(\frac{\partial P}{\partial \rho}\right)_{s}}[/tex]

    which, for an ideal gas, becomes

    [tex]c = \sqrt{R\ T \frac{C_{p}}{C_{v}}[/tex]

    So Stonebridge was correct when saying that the sound speed in air will increase with the square root of the air temperature.
     
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