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Why does the sound in a glass chnage as your fill it up with water?

  1. May 15, 2005 #1
    why does the sound in a glass chnage as your fill it up with water??????

    Hey everyone, does anyone know why the sound changes in a glass as you fill it up with water???? I think it has something to do with resonance
     
  2. jcsd
  3. May 15, 2005 #2
    Yeah, the water slows down the vibration of the glass.
     
  4. May 15, 2005 #3

    chroot

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    It has nothing per se to do with the glass itself, or any vibrations therein.

    The inside of a drinking glass is a resonant cavity with one open end, much like an organ pipe. As you fill the glass with liquid, the length of the pipe is decreased, and the pitch of the "note" increases.

    - Warren
     
  5. May 15, 2005 #4
    To start with lets remember that sound is vibration transferred by matter.

    When you are adding water to your glass, you are causing particles to vibrate. As you add liquid to the container, the space for these particles to vibrate gets smaller.

    A particle in a smaller space willl produce shorter waves. So, a smore liquid is added, the space become smaller and so the waves become shorrter, increeasing the pitch of the sound you hear.

    Regards,

    Ben
     
  6. May 15, 2005 #5

    chroot

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    BenGoodchild,

    The phenomenon of sound is not caused by particles vibrating. It's caused by waves of compression and rarefaction which propagate through the medium.

    The phenomenon at work here is that of standing waves -- the resonant frequencies of an open-ended pipe are those which allow a (half-)integral number of wavelengths to fit inside the cavity. The closed end has to be a pressure node, while the open end has to be a pressure anti-node.

    - Warren
     
  7. May 15, 2005 #6
    Sound is a series of mechanical compressions and rarefactions or longitudinal waves that successively pass one into another and propagate through materials (medium) that are at least a little compressible (solid, liquid or gas but not vacuum). In sound waves parts of matter (molecules or groups of molecules) move in a direction of the spreading of the disturbance (as opposite to transversal waves). The cause of sound waves is called the source of waves, e.g. a violin string vibrating upon being b

    Sound is a compression waveform created by the vibration of some object. Sound moves through air or other materials. The characteristics of sound are that it has amplitude, wavelength, frequency and velocity. Sound must cause another object to vibrate to be detected.

    Are two definitions of sound. And i believe you ar flawed in your thought and logic - what is causing the waves of compression and rarefaction? If not something vibrating?
    Do they just spontaneously appear?!

    Regards,

    Ben
     
  8. May 15, 2005 #7

    Hurkyl

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    This reminds me of a related quesiton I've had:

    Squeezing a plastic bottle lowers the sound it makes when you blow across the mouth. Why is that?

    (More specifically, when you squeeze the bottle so it deforms, rather than holding onto the bottle which dampens the sound)
     
  9. May 15, 2005 #8

    chroot

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    BenGoodchild,

    Do not post text from other websites here without providing proper credit to the original source.

    I am not arguing with your choice of the word 'vibration,' I am arguing with your choice of the word 'particle.' The sound in a glass results mostly from the vibration of the surface of the liquid. It has nothing to do with the individual particles which make up the liquid (or air).

    - Warren
     
  10. May 15, 2005 #9
    en.wikipedia.org/wiki/Sound is one of the links i cannot find the other!

    If the liquid is vibrating, the particles must themselves be moving. Maybe not vibrating but moving :tongue2: !

    I know I was a bit off there so sorry!!

    Regards,

    Ben
     
  11. May 15, 2005 #10

    Hurkyl

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    Also, the distance through which the individual particles oscillate affects the amplitude (volume). It has little to do with the frequency (pitch).
     
  12. May 15, 2005 #11
    The sound disturbance travels in space. There is energy transport (the disturbance propagates),but there is no net transfer of mass (no convection). Each particle in the fluid moves back and forth about one position. In general, sound waves in any medium can be a mixture of longitudinal and shear waves, depending primarily on the boundary conditions.
    See http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html for animations of longitudinal and shear waves.

    Longitudinal Wave – Simplest type of wave is compressional (or longitudinal wave) where the particle oscillation is in the same direction as the energy transport. The disturbance propagates in the direction of the particle motion. This is the predominant mechanism in fluids and gases because shear stresses are negligible.

    Shear Wave – The particle motion direction is orthogonal (perpendicular) to direction in which the disturbance (and the energy) propagates. In solids, you can have transverse shear and torsional waves. Bending waves (in a beam or plate), and water waves are a mixture of shear and longitudinal waves.

    Taken from www.mne.psu.edu/lamancusa/me458/5_physics.pdf

    Regards,

    Ben
     
  13. May 16, 2005 #12

    Galileo

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    Like Chroot said, the mechanism is like an organ pipe. The filling of the glass or bottle causes standing waves which get shorter as the glass gets fuller.

    The same thing happens when you blow over the opening of a bottle. The fuller the bottle, the higher the pitch.

    Contrast the case you get by rubbing your finger gently along the rim of a wine glass, or by hitting it with a spoon. This sound is produced by the vibration of the glass and has to do with the resonance frequency of the glass. In this case, filling the glass with water will lower the produced pitch, since the glass has to displace more mass.
     
  14. May 16, 2005 #13
    This intrigued me. In an organ pipe the air column is vibrated by a separate stream of air directed at the sharp edge of an opening in the side of the pipe. It is the fluttering of that directed stream back and forth, first to the interior of the pipe, then to the exterior, that causes the pressure differentials in the air sitting in the pipe.

    In the case of the glass, I couldn't see anything regular enough to call a "standing wave". I filled a glass out of the tap just now, and it sounds like random noise, many frequencies, which is the sound of the falling water hitting the water already in the glass. The increasingly shorter glass seems to be acting as a kind of variable Helmholtz resonator, picking out, and resonating to, the frequency contained in the many frequencies of the falling water, that happens to match it's resonant frequency at any given time.

    It seems to be rather like what would happen if you went to a noisy place with a varable length tube ( say a telescope with the lenses removed), put one end of the tube to your ear, and changed the length of the tube. No matter the length of the tube, there would be some sound source out there at the right fequency to make it resonate.

    Does the fact the source of the sound is "random" noise make it something other than a standing wave?
     
    Last edited: May 16, 2005
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