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B Harmonics on the soda bottle

  1. Nov 28, 2017 #1
    I saw a question
    "If you blow across the open end of a soda bottle and produce a tone of 250 Hz, what will be the frequency of the next harmonic heard if you blow much harder?"
    the answer is 750 Hz
    but I'm curious about "if you blow much harder" part, is it really depends on how much harder you blow or something else?
  2. jcsd
  3. Nov 29, 2017 #2


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    Do the experiment and you'll be the expert !
  4. Nov 29, 2017 #3
    When you run the experiment check how the frequency changes. Jumping an octave is what I'd expect (from 250 Hz to 500 Hz).
  5. Nov 29, 2017 #4


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    I think the point is that it is closed at one end and open at the other; there is a node at the closed end and an antinode at the open end, so it goes from 1/2 wavelength to 3/2 wavelength.
  6. Nov 29, 2017 #5
    Didn't give that any thought. I believe you have the right of it.
  7. Nov 29, 2017 #6
    isn't that about the speed of sound, if it is right how it much harder blowing effect on it. What is the logic here can anyone explain?
  8. Nov 29, 2017 #7
    The speed of sound is near 750 MPH, 750 Hz is oscillations per second...
  9. Nov 29, 2017 #8


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    Think about the speeds of the molecules which are needed for each harmonic mode.
  10. Nov 29, 2017 #9


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    I think this is pretty complicated, since a bottle like that is an example of a Helmholtz resonator. The column of air in the neck of the bottle is acting like the piston, and the air in the main portion of the bottle is acting like the spring. The basic linear theory is pretty simple - it is explained in basic sophomore level physics texts (eg Electromagnetic Vibrations, Waves and Radiation by Bekefi and Barrett). The harmonics are not as easy for me to understand. A quick google search did find an article that may be of interest:

  11. Dec 4, 2017 #10
    thank you
    the video on the page clearly shows which harmonic occurs depend on the speed of air that we blow. I cant reach the article it requires purchase the article but video was enough for me
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