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B What's the best way to visualize a soundwave? and more.

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  1. Apr 12, 2016 #1
    Hey, I have been searching the web, and have some unanswered questions regarding waves:
    1) I understand that you measure a sound wave's wavelength between two crests / areas of maximum compressions. Why do these compression areas occur? I thought the wave just moves on until it fades out.
    2) I've seen descriptions of soundwave as a sinus function - why does it take that form, and not a linear one, for example?
    3) Why when you drop a single drop of water (or a pebble) into a pond, it creates several concentric rings, and not one?
    Thanks
     
  2. jcsd
  3. Apr 12, 2016 #2

    sophiecentaur

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    1. The object that moves, generating the sound wave will push the air this way and that way, producing the compressions and rarefactions.
    2. Only a sinusoidal vibration produces a sinusoidal sound wave. Musical instruments produce waves that are far from sinusoidal. I guess the reason for your thinking that sine waves are necessarily is the simplified diagrams shown in some text books. Complicated waveforms can be broken down into sinusoidal components.
    3. The answer to this is not simple and it's based on the Maths of what happens to the water that your pebble has displaced. It is possible to generate a single pulse on the surface of water but it requires a different mechanism to excite it (pushing a piston down into the water with the appropriate motion will do it).
     
  4. Apr 12, 2016 #3

    BvU

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    What's the best way to visualize a soundwave?

    Google ! ("sound wave" or "sound wave diagram")

    1) Because there is someting that moves back and forth (*) at the source of the sound
    (*) or creates rapid pressure fluctyations in another way, e.g. like vocal chords or organ pipes do
    The wave propagates in all directions. It fades out mainly because at twice the distance there is 4 times the area to vibrate.

    2) if something vibrates, the simplest case is that the restoring force is proportional to the deviation from equillibrium. That gives rise to sinus-like motion like with a vibrating spring/mass

    3) Look carefully. You see a disruption of equilibrium. it spreads out but it also bounces back a few times.

    Hee, sophie beat me. I hope we agree in general... :)
     
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