Kaplan MCAT Physics and Math Review: Created for MCAT 2015 (Kaplan Test Prep) by Kaplan

Author:Kaplan
Language: eng
Format: epub, mobi
Publisher: Kaplan Publishing
Published: 2014-09-09T07:00:00+00:00

RESONANCE

Why are clarinets, pianos, and even half-filled wine glasses considered musical instruments, but not pencils, chairs, or paper? This discrepancy has much to do with the natural (resonant) frequencies of these objects. Any solid object, when hit, struck, rubbed, or disturbed in any way will begin to vibrate. Tapping a pencil on a surface will cause it to vibrate, as will hitting a chair or crumpling a piece of paper. Blowing air pressure between a clarinet reed and a mouthpiece, striking a taut piano string, and creating friction on a wine glass’s surface will also cause vibration. If the natural frequency is within the frequency detection range of the human ear, the sound will be audible. The quality of the sound, called timbre, is determined by the natural frequency or frequencies of the object. Some objects vibrate at a single frequency, producing a pure tone. Other objects vibrate at multiple frequencies that have no relation to one another. These objects produce sounds that we do not find particularly musical, such as tapping a pencil, hitting a chair, or crumpling paper. These sounds are called noise, scientifically. Still other objects vibrate at multiple natural frequencies (a fundamental pitch and multiple overtones) that are related to each other by whole number ratios, producing a richer, more full tone. The human brain perceives these sounds as being more musical, and all nonpercussion instruments produce such overtones. Of note for the MCAT, the frequencies between 20 Hz and 20,000 Hz are generally audible to healthy young adults, and high-frequency hearing generally declines with age.

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