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Sound and clapping

  1. Sep 7, 2004 #1
    Sound and clapping....

    To produce sound something needs to oscillate (eg - a tuning fork) in order to "hit" the air molecules and produce compressions and rerefactions. My question is what actually oscillates to produce the sound when you clap your hands or hit something?

    Thanks in advance. :wink:
     
  2. jcsd
  3. Sep 7, 2004 #2
    There is really no oscillation. From a clap or a bang it’s just single compression wave.
     
  4. Sep 7, 2004 #3

    Tide

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    The air oscillates - over a very broad band of frequencies. :-)
     
  5. Sep 7, 2004 #4
    LoL. Well I guess Tide's answer is more correct than mine.
     
  6. Sep 7, 2004 #5
    No, i dont think you've quite understood what i meant - when you clap what is it that oscillates to cause the air to oscillate in a wave? eg - tuning fork = tuning fork vibrates, then air vibrates. BUt when you clap your hands they dont vibrate.
     
  7. Sep 7, 2004 #6

    Tide

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    You have to understand fundamentally what sound is. Sound is a disturbance in a medium (such as air) that propgates. Simply by moving your hands you create sound - the frequencies are usually just too low for you to hear but if you move them fast enough you can hear the "whooshing" sound. When you clap your hands together, that instant when your hands are just meeting causes a move severe disturbance in the air than just waving them about.

    The oscillations occur when the air molecules rushing away from the site of the initial disturbance pile up and leave a partial vacuum behind them. This partial vacuum will tend to pull the air molecules back, they overshoot and pile up the other way and on and on.
     
  8. Sep 7, 2004 #7

    Chi Meson

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    Notice the difference between the sound of a tuning fork and a hand clap. The tuning fork is sustained due the fact that the fork oscillates. A hand clap is not sustained since it is a single "pulse" disturbance (as already mentioned. So not all noises are caused by oscillations.
     
  9. Sep 7, 2004 #8

    HallsofIvy

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    This statement "To produce sound something needs to oscillate (eg - a tuning fork) in order to "hit" the air molecules" is incorrect. To produce a sustained note, you need oscillation but to produce just a "sound" you don't need oscillation.
     
  10. Sep 8, 2004 #9

    DaveC426913

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    There is oscillation, but it is short-lived and it is across a wide range of frequencies.

    Consider, when you drop a pencil on the ground (forget sound for a second, think of motion) - it doesn't just *thunk*! once and stop. Nor does it bounce perfectly (oscillate) like a ball. What it does, is "clatter" for a bit.

    When you clap, your hands don't impact in one fell swoop, but over a very short time - there's more than one impact in there. Additionally, the air molecules get strongly jostled about. They jostle each other and jostle back. Like the pencil, the molecules "clatter" to a stop. The waves sent out from this are of a range of frequencies and short-lived.

    Another example: think of a beaded curtain - the kind that hung in doorways up until the flower children grew up. Hit it with your fist - just once, quickly. What do the beads do? Think of the beads as air molecules.
     
    Last edited: Sep 8, 2004
  11. Sep 8, 2004 #10

    krab

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    How do you define osillation? I think Halls' point is that one 'bump' is not an oscillation. The easiest demonstration is using a clothesline. Hit it smartly at one end, and only one pulse travels down the line, hits the end and is reflected. This is similar to a sound pulse, except that it's 1D and sound is in 3D. Of course, it can be Fourier-analyzed into many (sustained) component frequencies phased in such a way that they all cancel for times longer than the pulse length, but that's only important if you are doing something like designing a speaker system to reproduce the sound.

    Just to add to Tide's description, it is the very last fraction of a mm before the hands come right together that squishes air out and causes the sound. This is because the air at that last point is squished out so fast that it piles up just around the impact site, thus creating a single compression pulse, that then travels to the ear, just like the pulse on the clothesline.
     
  12. Sep 8, 2004 #11

    mee

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    I think it is probably more correct to say that to easily produce a sustained note one can use occillation. One can also produce a sustained note by rolling a steel clyinder across a plane for example perhaps.
     
  13. Sep 9, 2004 #12

    Mk

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    Sound is a distubance in any medium.

    I heard sound travels more swiftly through steel than air. Is that because the steel has less area to move around, and transfers the sound quicker?
     
  14. Sep 9, 2004 #13
    when you strike our one hand on the other the air between them escape quickly creating low pressure area there. After this stage the air moves to the area of low pressure hence a wave is formed, a sound wave.
     
  15. Sep 9, 2004 #14

    Tide

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    The speed of sound in a solid is determined essentially by its stiffness (Young's modulus) as well as the density of the material.

    [tex]v = {\sqrt {\frac {Y}{\rho}}[/tex]
     
  16. Sep 13, 2004 #15

    DaveC426913

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    Yes, and in an idealized thought experiment representing sound, you'll get that.

    But you don't get it from clapping hands. There is *always* reverberation.
     
  17. Sep 13, 2004 #16
    Some more adept will get the idea, if said the billiard balls as they crack, might have idealizied this to a ping, and what have we describe of the quantum world?

    Anyone one know what I am comparing?

    Leave it to the brights minds to not ever loose their train of thought.

    From one challenge, to another :smile:
     
    Last edited: Sep 13, 2004
  18. Sep 13, 2004 #17

    LURCH

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    I love this thread! Leave it to the scientific mind to ask, "What is the sound of two hands clapping?" !
    I think this is the very heart of the question. If the air pressure against your eardrum starts out at one pressure (about 14 psi), and goes to a higher pressure, then returns to the original pressure, does this not constitute a single oscilation?
     
  19. Sep 13, 2004 #18

    Chi Meson

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    Oscillation is usually defines as a regularly repeating, or periodic vibratory motion. One could argue over the semantics, but I for one am happy with this definition. :)
     
  20. Sep 13, 2004 #19

    Tide

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    Yes, and the air molecules that transmit the sound do just that! They oscillate even if it isn't forever. By analogy, a damped harmonic oscillator is still an oscillator.
     
  21. Sep 14, 2004 #20

    Chi Meson

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    I get your point. But (again IMO) if the nature of something is to perpetually exhibit critically damped oscillation (as with a sound pulse through air) I would prefer not yto think of it as an "oscillation."

    I hope we all understand that this is really nit-picking of the highest order. For some reason it's fun.
     
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