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A Few Questions about Resonance

  1. Mar 3, 2013 #1
    Hello, fellow Physicians! Wait, that's not right. . .

    Anyways, I've been teaching myself a little about resonance just for my own ends, and I have a few questions about resonance, specifically in relation to libation holders.

    First of all, WHY does hitting a wine glass produce its resonant frequency?
    Secondly, if I were to break a wine glass, would it have to be crystal rather than glass, or would I just require a higher amplitude of sound to fracture the (glass) wine glass?

    (I apologize if this is in the wrong place. This is my first time here, but I hope to be a repeat visitor)
     
  2. jcsd
  3. Mar 3, 2013 #2

    Drakkith

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    Staff: Mentor

    Any non-resonant frequencies are quickly attenuated I believe.
     
  4. Mar 3, 2013 #3
    When you hit an object, a sound wave travels at its characteristic speed in said object, if you hit the object at one end, the wave will travel all the way to the other and then reflect, then it will travel back and reflect again. It will resonate because it's in the nature of sound waves to do this, as this is exactly what happens when an object is in resonance--that is, the oscillating force is in conjecture with the wave in the object.
     
  5. Mar 4, 2013 #4

    Bobbywhy

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    Gold Member

    Daolothe, Welcome to Physics Forums!

    May I suggest you learn about Mechanical and acoustic resonance? For an introduction, start here:
    http://en.wikipedia.org/wiki/Resonance

    Next, study and learn the details of acoustic resonance:
    Acoustic resonance is the tendency of an acoustic system to absorb more energy when it is forced or driven at a frequency that matches one of its own natural frequencies of vibration (its resonance frequency) than it does at other frequencies.
    Like mechanical resonance, acoustic resonance can result in catastrophic failure of the vibrator. The classic example of this is breaking a wine glass with sound at the precise resonant frequency of the glass; although this is difficult in practice. http://en.wikipedia.org/wiki/Acoustic_resonance

    Now that you’ve learned the physical mechanisms involved, go here and you can learn how to break a wineglass at home:
    http://www.physics.ucla.edu/demoweb...fects_of_sound/breaking_glass_with_sound.html

    Cheers, Bobbywhy
     
  6. Mar 5, 2013 #5
    Any wave in matter travels at a speed that is determined only by the characteristics of the material in which it's traveling, not by how it's produced. See this in sound waves, the speed of sound will not change no matter how loud you produce a sound. This has to do with the fact that waves are produced by the interactions between the individual particles that make up the material.

    Another good example, go find a slinky stretch it out and send a wave down one end by scrunching up one end, and suddenly releasing it. The speed in which that 'slinky wave' propagates, will always be the same, as it has nothing to do with wave production, but on the characteristics of the slinky.

    Hitting a wine glass is creating a matter wave, and just like sound the interactions between the individual glass particles determines the speed of the wave no matter how hard you hit it. The shape of the wine glass factors in for the sound production, but the fact remains that if you hit a glass rod on a table you'd still get a tone. It's simply because the frequency at which air molecules are displaced by the constant speed matter wave is the same wherever you look on the glass.

    Take any different material whose characteristic matter wave speed is different, and you may get sound below or above our hearing range.

    To break the glass, you need a producer of sound that can produce a tone at the glass's resonant frequency, and you need that producer of sound to be able to pump out the intensity needed to stretch the glass itself to it's breaking point. In other words you'd need a sound producer that increases the glass's oscillations faster than the environment can dissipate them. You need a sound producer that's loud, and of the right tone, crystal or not. Crystal is simply easier to shatter than glass. As for which has a more obtainable resonant frequency I'm not sure.

    Hopefully I helped, and hopefully I'm not grossly wrong.
     
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