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Flying circus of physics

Pub trick --- musical wineglass (do you need a gift idea for the season?)

Monday, December 01, 2014

Pub trick -- musical wineglass (do you need a gift idea for the season?)
Jearl Walker
December 2014  For the holidays, I gave myself a gift, a musical wineglass from Uncommon Goods.

The wineglass has thin walls so that when I rub a wet finger around the rim, I can easily cause the wall to oscillate, which sends out a sound wave. The frequency of the oscillations (and thus of the sound waves) depends on the depth of wine or any other liquid in the glass. In general, adding more wine makes the oscillations more sluggish and thus lowers the frequency.

Of course, other thin-walled wineglasses will do the same but the delight of this particular wineglass is that marks have been put on the wall showing me what the wine level should be in order to get a particular note. For example, in my photograph, I have added enough liquid (stout, not wine, for me) to the level marked G# so that the oscillations produce a G-sharp note.

Here is a link to a video produced by Uncommon Goods to demonstrate their wineglass musical capabilities. Jingle Bells

From The Flying Circus of Physics book, here is my explanation for the physics of a musical wineglass. As your finger rubs against the rim, the finger and rim are continually undergoing sticking and slipping. During the sticking phase, the rim is pulled very slightly in the direction of your finger’s motion, distorting the rim’s shape. During the slipping phase, the rim breaks free of your finger and attempts to regain its original shape, but it ends up oscillating. The strongest oscillation is said to be resonance, in which the rim oscillates as shown in the overhead view of this figure:

Here is a slow-motion video showing the rim oscillations being driven acoustically by intense sound waves instead of a rubbing finger. Eventually the oscillations are large enough to break the glass.

In playing a wine glass, the oscillation pattern follows your finger around the rim, producing a pulsation to the sound (it comes and goes with a frequency of a few hertz, depending on the speed of the finger on the rim). The frequency at which the rim pushes on the air and the frequency that you hear are roughly proportional to the rim thickness and inversely proportional to the square of the glass’s radius at the open end. Thus, generally the frequency is higher for a thicker rim and smaller radius. If you add liquid to the glass, you lower the resonant frequency because the liquid’s mass decreases the rate at which the glass wall can oscillate.

Some musicians are skilled at playing music on an array of glasses containing various levels of liquid. Here is my favorite example:

Dots · through ··· indicate level of difficulty
Journal reference style: author, journal, volume, pages (date)
Book reference style: author, title, publisher, date, pages
· Schufle, J. A., “Answer: Chinese brass water-spouting bowl,” Isis, 72, No. 261, 86-88 (1981)
·· Apfel, R. E., “Whispering waves in a wineglass,” American Journal of Physics, 53, 1070-1073 (1985)
··· Rayleigh, Lord (J. W. Strutt), The Theory of Sound, volume 1, 2nd edition, 1894, reprinted by Dover in 1945, pages 383-389
··· French, A. P., “In vino veritas: a study of wineglass acoustics,” American Journal of Physics, 51, 688-694 (1983)
· Meyer, V., and K. J. Allen, “Benjamin Franklin and the glass Armonica,” Endeavour, 12, No. 4, 185-188 (1988)
·· Rossing, T. D., “Wine glasses, bell modes, and Lord Rayleigh,” Physics Teacher, 28, 582-585 (December 1990)
· Fischer, R. M., (letter) “Polished performance,” Science News, 142, 115 and 124 (24 August 1991)
· Rueckner, W., D. Goodale, D. Rosenberg, S. Steel, and D. Tavilla, “Lecture demonstration of wineglass resonances,” American Journal of Physics, 61, No. 2, 184-186 (February 1993)
·· Rossing, T. D., “Acoustics of the glass harmonica,” Journal of the Acoustical Society of American, 95, No. 2, 1106-1111 (February 1994)
··· Hsieh, D. Y., “Water waves in an elastic vessel,” Acta Mechanica Sinica (English Series), 13, No. 4, 289-303 (November 1997)
· Sample, I., “The maddening truth about martini glasses,” New Scientist, 168, No. 2265, 20 (18 November 2000)
· Planinsic, G., “More fun with singing wineglasses,” Physics Teacher, 38, 41-42 (January 2000)
· Bermer, B., “Resonant wineglasses and Ping-Pong Balls,” Physics Teacher, 38, 269-270 (May 2000)
··· Chen, K-W., C-K. Wang, C-L. Lu, and Y-Y. Chen, “Variations on a theme by a singing wineglass,” Europhysics Letters, 70, No. 3, 334-340 (1 May 2005)
··· Chen, Y.-Y., “Why does water change the pitch of a singing wineglass the way it does?” American Journal of Physics, 73, No. 11, 1045-1049 (November 2005)
··· Jundt, G., A. Radu, E. Fort, J. Duda, H. Vach, and N. Fletcher, “Vibrational modes of partly filled wine glasses,” Journal of the Acoustical Society of America, 119, No. 6, 3793-3798 (June 2006)
· Uchida, K., and K. Kishi, “Vibrational analysis of glass harp and its tone control,” Acoustical Science and Technology, 28, No. 6, 424-430 (2007)
··· Joubert, S. V., T. H. Fay, and E. L. Voges, “A storm in a wineglass,” American Journal of Physics, 75, No. 5, 647-651 (July 2007)
··· Courtols, M., B. Gulrao, and E. Fort, “Turning the pitch of a wine glass by playing with the liquid inside,” European Journal of Physics, 29, 303-312 (2008)
· Arane, T., A. K. R. Musalem, and M. Fridman, “Coupling between two singing wineglasses,” American Journal of Physics, 77, No. 11, 1066-1067 (November 2009)

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