![]() The second harmonic is shown in Figure 2 the third harmonic in Figure 3 and so forth (the whole set of harmonics beyond the first are called the The simplest, called the fundamental (or the first harmonic), appears in Figure 1, which shows the outermost extensions of the string carrying out this vibration. However, its motion can be analyzed into a combination of a large number of simple motions. The string may vibrate in a variety of different ways, depending upon whether it is struck or rubbed to set it in motion, and where on the string the action took place. While these vibrations are not an example of sound, they do illustrate many of the properties of importance in acoustics as well as in the production of sound. To understand some of the fundamentals of sound production and propagation it is instructive to first consider the small vibrations of a stretched string held at both ends under tension. Sound may also be caused by a large disturbance that causes parts of a body to vibrate, such as sounds caused by a falling tree. Some examples are as simple as a string in a violin or piano, or a column of air in an organ pipe or in a clarinet some are as complex as the vocal chords of a human. There are many examples of vibrating bodies producing sounds. The term supersonic refers to bodies moving at speeds greater than the speed of sound, and is not normally involved in the study of acoustics. When the rate of vibration is below the range of human hearing, the sound is termed infrasonic when it is above that range, it is called ultrasonic. However, the only vibrations that are considered sound (or sonic vibrations) are those in which the medium vibrates in the same direction as the sound travels, and for which the vibrations are very small. ![]() Sound may be produced when a material body vibrates it is transmitted only when there is some material body, called the medium, that can carry the vibrations away from the producing body it is received when a third material body, attached to some indicating device, is set into vibratory motion by that intervening medium. The word acoustic was derived from the ancient Greek word akoustikos, meaning able to be heard. Acoustics, sometimes called acoustical physics, is the science that deals with the production, transmission, reception, control, and effects of sound in gases, liquids, and solids.
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