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Equilibrium of air molecule

  1. Apr 27, 2013 #1
    I have an air molecule moving because of a sound wave.

    f of sound wave = 500 Hz
    wavelength of sound wave = 0.68 m

    How fast is the air molecule moving in its equilibrium position?

    Is it in equilibrium at V max? Would this be where the position = 0?
  2. jcsd
  3. Apr 28, 2013 #2


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    Gold Member

    morgan8222, here is some information about sound in air. Note that it does not directly answer your question because it refers to a "parcel of air" and NOT to an individual air molecule.

    "Particle velocity is the velocity v of a particle (real or imgined) in a medium as it transmits a wave. In many cases this is a longitudinal wave of pressure as with sound, but it can also be a transverse wave as with the vibration of a taut string.
    When applied to a sound wave through a medium of a fluid like air, particle velocity would be the physical speed of a parcel of fluid as it moves back and forth in the direction the sound wave is travelling as it passes.
    Particle velocity should not be confused with the speed of the wave as it passes through the medium, i.e. in the case of a sound wave, particle velocity is not the same as the speed of sound. The wave moves relatively fast, while the particles oscillate around their original position with a relatively small particle velocity. Particle velocity should also not be confused with the velocity of individual molecules.
    In applications involving sound, the particle velocity is usually measured using a logarithmic decibel scale called particle velocity level."

    May I ask the source of your question? Members here in Physics Forums always want to be sure a person gets a satisfactory and scientifically correct response to her question. If you can provide the background (origin) and more detail of the exact conditions, perhaps a member can give the exact response you need.
    Last edited: Apr 28, 2013
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