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How does sound travel?

  1. Aug 14, 2007 #1
    How does sound travel???

    Does sound travel merely by vibration of particles in the media? To my imagination, the sound propagates as follows:

    The atom/molecule close to the sound source moves towards the neighbouring sides. The repulsion from one electron in the atom moves the electron in the neighbouring atom. Also, the repulsion from one nucleus causes the neighbouring nuclueus to vibrate.

    Is the above statement true? If so, sound should be explained by kinetic and electric forces, right? Can I say sound energy is just another mechanical/electrical movement of particles and it just happened to have a big biological importance (our ear cells can respond to some frequency band). I mean, in physics, sound is not a fundamental form of enery like charge, light etc...

    Thanks,
    .joby
     
    Last edited: Aug 14, 2007
  2. jcsd
  3. Aug 15, 2007 #2

    AlephZero

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    I would say yes.

    As far as the physics goes, sound is no different from any other sort of wave propagation.

    Of course the biology and psychology of sound are separate areas of study, where sound is considered from the point of view as "what you hear" as well as "what is measured by physics lab equipment".
     
  4. Aug 15, 2007 #3

    DaveC426913

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    You are correct.
     
  5. Aug 15, 2007 #4

    Danger

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    I've never heard (no joke intended) of that differentiation. The psychology aspect makes sense, but from a biological standpoint the body still responds to both infrasound and ultrasound even if we don't 'hear' it. Since it's not a phenomenon that can be ignored, do biologists refer to it by another term if it's inaudible? (That isn't a facetious question; I really don't know.)
     
    Last edited: Aug 15, 2007
  6. Aug 15, 2007 #5
    While you are correct that it is just mechanical and electrical movement of particles, I think you are missing the connection between it and the biological importance of it. Sound was present and ears evolved in order to hear it to gather more information and thus to survive more efficiently, much in the same way that light was present and then eyes evolved to take advantage of it. The presence of sound is intimately entwined with the evolution of the ear. It didnt "just happen to be so".
     
  7. Aug 15, 2007 #6

    Danger

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    Good point. I totally missed that part of the question.
    It's similar to 'creationists' pointing out that Earth is perfectly designed for human life. Of course it it, because we evolved to fit our environment. If our ancestral microbes had been on Mars, then that would be perfectly designed for us.
     
  8. Aug 15, 2007 #7
    True. I should admit, when I think deep into physics and chemistry, I just feel myself as just a bunch of atoms and subatomic particles, grouped together by some interatomic forces. That makes me miss some other important aspects, but you know, helps me less fearful about my own death:)

    Thanks for reminding.
     
  9. Aug 15, 2007 #8

    Danger

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    The only comfort for an Atheist. (Well, the multi-verse concept works very well for me. I've already died hundreds of trillions of times in other quantum branches... but I'm still alive in the one that I'm conscious of.)
     
  10. Aug 15, 2007 #9
    I don't think energy really has any fundamental form.
     
  11. Aug 15, 2007 #10

    Danger

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    'Sound' isn't energy at all; it's our interpretation of pressure waves, which are very real but not 'fundamental' in the way that you mean. The propogation thereof does, of course, depend upon the atomic structure of the conductive medium.
    I can't help bringing up the old question: 'If Helen Keller fell over in a forest, would anyone hear it?'
     
  12. Aug 15, 2007 #11

    rcgldr

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    Sound travels as 3-dimensional pressure waves. This wiki article covers the basics:

    http://en.wikipedia.org/wiki/Sound

    Sound is a form of power, again I refer to a Wiki article:

    http://en.wikipedia.org/wiki/Sound_power

    Decible system:

    http://en.wikipedia.org/wiki/Decibel

    Hearing is bascially logarithmic, a 10db increase in sound level is perceived to be a doubling in "loudness".

    http://www.phys.unsw.edu.au/jw/dB.html

    Another tidbit of info: The "mean" speed of air molecules at around 15C is about 500 m/s, faster than the speed of sound which is 340m/s (at 15C).

    Maybe parts of the body, but once below or above a frequency range, the movement of the eardrum is either too slow or too small to stimulate any significant response by the nerves that respond to sounds, regardless of the power. A person could physically feel very powerful low frequency sound waves, but wouldn't be able to hear them, similarly a person could get heated up by microwaves, but wouldn't be able to see them.
     
    Last edited: Aug 15, 2007
  13. Aug 15, 2007 #12
    Can I say the sound frequency is also a factor of the medium? Can I make an an ultrasound wave human-audible by passing it through a different medium?
    Also, does the frequency change over a distance?
     
  14. Aug 15, 2007 #13

    Pythagorean

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    Distance alone attenuates amplitude, but doesn't change frequency.

    I can't remember whether mediums affect frequency. I want to say no, it just affects propagation speed.
     
  15. Aug 15, 2007 #14

    rbj

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    i don't think that charge is a fundamental form of energy, is it? it's a pretty fundamental property of some particles of matter.

    this thing with atoms repulsing each other is something that happens in air (or some fluid) even when there is no sound. i think the best way to understand it is with the ideal gas law, Newton's laws, and the continuity equation. you can set up a wave equation and solve it.
     
  16. Aug 15, 2007 #15

    Danger

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    I agree with Pythagorean about that; I also don't know about any medium which alters the pitch. As for distance, it does in one regard: if the source and the listener are moving toward or away from each other, the Doppler shift changes the frequency.
     
  17. Aug 16, 2007 #16

    DaveC426913

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    This whole pressure wave thing is passe.

    The modern model is that sound travels in discrete little bundles called mp3 players.
     
  18. Aug 16, 2007 #17

    Danger

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    Wow! I never saw the papers on that one. If it turns out that sound really is quantized, we might be able to use it in semi-conductor technology! (It's gotta be faster than electricity, right?)
     
  19. Dec 14, 2008 #18
    Re: How does sound travel???

    By mouth
     
  20. Dec 15, 2008 #19

    Ranger Mike

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    Re: How does sound travel???

    I Believe this theory was was introduced by Professor Jimi Hendrix in 8 track form circa 1967
     
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