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Speed of sound

  1. Mar 31, 2005 #1
    If I have a glass of water and tap it with a spoon there will be a sound. If I change the speed of sounf by adding something the sound will change. What is the connection between change in speed of sound and the change in sound?

    Does the frequence change then or what?
  2. jcsd
  3. Mar 31, 2005 #2
    The speed of sound isnt changing, the wavelength and frequency are.

    The velocity of any wave is the product of the wavelength and frequency.

    The changei nthe sound you hear is due to a change in the frequency of the wave you hear.
  4. Apr 1, 2005 #3
    When you change the media, the wave that used to pass through that media is distorted. It depends on "something" you add. Also it depends on what you call "change in sound".

    Once we analysed the noise produced by a spoon hitting the fresh & hot cup of coffee. (oh we drunk it so much back then :rofl:)
    the reason of the dump noise was the presence of small particles of coffee/sugar/whatever all over in the cup and the air bubbles in the upper layers. (such things have a name: fine-dyspersated two-phased system!)
    Well, as far as it could be done experimentally, we analized the evaluation of noise's spectrum versus time straight away after the coffee-creation, and even managed to derive certain formulas for induced wave frequencies, which showed a good coincidence with the observed ones!

    So, basically it's difficult to predict what will change in your case, at it really depends on the properties of the matter you put in the glass.
    Even if you poor the same water - there is no guarantee that you'll receive the same sound frequency after hitting the cup: a slight change in water level changes the resonant properties of the whole system (cup+water), so the major range of frequencies outside of the resonance peak will mainly fade out, and the ones you hear most - are resonant frequencies...
  5. Apr 1, 2005 #4
    I created the scenario, so if I say that i change the sound of speed somehow, it IS changed.

    If i pour in something, that neccesarilly doesnt create airbubbles, the density will chnage which will lead to a change in speed of sound.

    My question was that how the chnage in speed of sound affects the pitch of the sound made when you tap the glass, if there is a change in pitch...
  6. Apr 1, 2005 #5
    wooow! how does the speed sound? :rofl:

    google for resonance. i can add nothing more, unless you specify the proper geometry of the system. After that it IS possible even to simulate the process, if the analitycal calculation is impossible
  7. Apr 1, 2005 #6


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    Staff: Mentor

    The speed of the sound in the glass/cup material (solid) and the speed of sound in the liquid do not change. The mode of vibration in the glass/cup vessel will change however. The frequency (pitch) changes (should increase) with the increasing mass as the liquid fills the cup. Also, there is the sound in air, above the liquid in the cup - that does not change either.
  8. Apr 1, 2005 #7
    oh it does. if i understood the problem correctly - the sound you speak about is coming from the body hitting cup. It comes to the observation point (above the cup) by two ways:
    1) scattered wave in the air (does not change)
    2) wave transmitter through the cup (does change)

    so generally the resultant sound changes...
  9. Apr 1, 2005 #8

    The speed of sound DOES change! i have said it three times.. when the density of the fluid is changed the speed of sound WILL change!

    My question, once again, is that how the speed of sound affects the pitch of the sound...
  10. Apr 1, 2005 #9
    If the speed changes, the frequency of the modes will all change. When you tap
    it, you will excite different modes which will all add together and make a different
    sound than the fluid with the other density.

    The frequency, speed, and amplitudes (for a given "tap" of the cup) will all change.
  11. Apr 2, 2005 #10
    thank you Antiphon... that was the sort of answer i was hoping for.. though I'm not sure of what you mean with "the modes"... but the frequency changes to chnage the pitch?
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