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The atmosphere exerts pressure on all objects in it. When a vibrating body moves in air, it creates slight disturbances of the AMBIENT atmospheric pressure. The AMPLITUDE of these pressure variations is called the sound pressure variation, whereas the effective pressure variation is 0.707 the maximum value. The oscillating variations in sound pressure (called the WAVEFORM of the sound) PROPAGATE in the form of a SOUND WAVE.
If two TONEs are about 15 Hertz or less apart, INTERFERENCE will result from their similar though not exactly identical frequencies. Gradually they will move out of PHASE until at 180
Sound at frequencies above the audible range, namely above 20 kHz, audible only to various non-human species. Because of its very short WAVELENGTH in the megahertz range, ultrasound is used as a safe alternative to X-ray photography in medical diagnosis. Ultrasound scanning is sometimes called sonography.
In music, an adjective referring to HARMONY and its principles. In ACOUSTICS, when a vibrating object, such as a string, is set in motion, it vibrates both as a whole, with a FREQUENCY called the FUNDAMENTAL, and, with lesser intensity, in sections as well. If these smaller lengths are integer fractions (1/2, 1/3, 1/4, ...) of the total length of the string, their frequencies of OSCILLATION are called harmonics, and are integer multiples of the fundamental.