RESONANCE: “The property whereby any vibratory system responds with maximum amplitude to an applied force having the frequency equal to its own.” In english, this means that any solid object that is struck with a sound wave of equal sound wave vibrations will amplitude the given tone. This would explain the reason why some singers are able to break wine glasses with their voice. The vibrations build up enough to shatter the glass. This is called RESONANCE. Resonance can be observed on a tube with one end open. Musical tones can be produces by vibrating columns of air. When air is blown across the top of the open end of a tube, a wave compression passes along the tube. When it reaches the closed end, it is reflected.
The molecules of reflected air meet the molecules of oncoming air forming a node at the closed end. When the air reaches the open end, the reflected compression wave becomes a rarefaction. It bounces back through the tube to the closed end, where it is reflected. The wave has now completed a single cycle. It has passed through the tube four times making the closed tube, one fourth the length of a sound wave. By a continuous sound frequency, standing waves are produced in the tube. This creates a pure tone. We can use this knowledge of one fourth wavelength to create our own demonstration. It does not only have to be done using wind, but can also be demonstrated using tuning forks. If the frequency of the tuning forks is known, then v=f(wavelength) can find you the length of your air column. Using a tuning fork of frequency 512 c/s, and the speed of sound is 332+0.6T m/s, temperature being, 22 degrees, substitute into the formula. Calculate 1/4 wavelength V=f(wavelength) wavelength=V/f =345.2 (m/s) / 512 (c/s) =0.674 m/c 1/4 wave. =0.674 (m/c) / 4 = 0.168 m/c Therefore the pure tone of a tuning fork with frequency 512 c/s in a temperature of 22 degrees would be 16.8 cm. The pure tone is C. If this was done with other tuning forks with frequencies of 480, 426.7, 384, 341.3, 320, 288, and 256 c/s then a scale in the key of C would be produced.
There are many applications of this in nature. One example of this would be the human voice. Our vocal chords create sound waves with a given frequency, just like the tuning fork. One of the first applications of the wind instrument was done in ancient Greece where the pipes of pan were created. Pipes of hollow reeds were bound together, all of different length. When Pan, the god of fields, blew across his pipes, the tones of a musical scale were heard. Later reproductions of the same type were created and musical instruments are heard all over the world thanks to the law of resonation.
Granet, Charles; Sound and Hearing; Abelard-Schuman, Toronto; 1965 Freeman, Ira M.; Sound and Ultrasonics; Random House; New york; 1968 Freeman, Ira M.; Physics Made Simple; Doubleday, New York; 1965 Jones, G.R.; Acoustics; English Univ. Press; London; 1967 White, Harvey E; Physics and Music; Saunders College, Philadelphia; 1980 Funk and Wagnall; Standard Desk Dictionary; Harper Row, USA; 1985
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