![]() Since there is a slight distance in position between the two ears of an animal, the sound may return to one of the ears with a bit of a delay, which also provides information about the position of the object. This gives information about the direction, size and shape of the object. Figure 14.9 shows a bat using echolocation to sense distances.Įcholocating animals identify an object by comparing the relative intensity of the sound waves returning to each ear to figure out the angle at which the sound waves were reflected. Since the speed of sound in air is constant, the time it takes for the sound to travel to the object and back gives the animal a sense of the distance between itself and the object. They locate an object (or obstacle) by emitting a sound and then sensing the reflected sound waves. It is used by animals such as bats, dolphins and whales, and is also imitated by humans in SONAR-Sound Navigation and Ranging-and echolocation technology.īats, dolphins and whales use echolocation to navigate and find food in their environment. The time for the echo to return is directly proportional to the distance.Įcholocation is the use of reflected sound waves to locate and identify objects. Since v = f λ v = f λ, the higher the speed of a sound, the greater its wavelength for a given frequency.įigure 14.9 A bat uses sound echoes to find its way about and to catch prey. If v changes and f remains the same, then the wavelength λ λ must change. However, the frequency usually remains the same because it is like a driven oscillation and maintains the frequency of the original source. The speed of sound can change when sound travels from one medium to another. Therefore, the relationship between f and λ λ is inverse: The higher the frequency, the shorter the wavelength of a sound wave. ![]() ![]() Recall that v = f λ v = f λ, and in a given medium under fixed temperature and humidity, v is constant. But the music from all instruments arrives in cadence independent of distance, and so all frequencies must travel at nearly the same speed. If this were not the case, and high-frequency sounds traveled faster, for example, then the farther you were from a band in a football stadium, the more the sound from the low-pitch instruments would lag behind the high-pitch ones. One of the more important properties of sound is that its speed is nearly independent of frequency. Just as a transverse wave alternates between peaks and troughs, a longitudinal wave alternates between compression and rarefaction.įigure 14.7 A sound wave emanates from a source vibrating at a frequency f, propagates at v, and has a wavelength λ λ. From this figure, you can see that the compression of a longitudinal wave is analogous to the peak of a transverse wave, and the rarefaction of a longitudinal wave is analogous to the trough of a transverse wave. ![]() Figure 14.4 shows a graph of gauge pressure versus distance from the vibrating string. But some of the energy is also absorbed by objects, such as the eardrum in Figure 14.5, and some of the energy is converted to thermal energy in the air. The amplitude of a sound wave decreases with distance from its source, because the energy of the wave is spread over a larger and larger area. For ordinary, everyday sounds, pressures vary only slightly from average atmospheric pressure. Gauge pressure is the pressure relative to atmospheric pressure it is positive for pressures above atmospheric pressure, and negative for pressures below it. The graph shows gauge pressure (P gauge) versus distance x from the source. You may recall from the chapter on waves that areas of compression and rarefaction in longitudinal waves (such as sound) are analogous to crests and troughs in transverse waves.įigure 14.4 After many vibrations, there is a series of compressions and rarefactions that have been transmitted from the string as a sound wave. Some of the energy is lost in the form of thermal energy transferred to the air. The pressure disturbance moves through the air as longitudinal waves with the same frequency as the string. regions are compressions, and the low pressure regions are rarefactions. This creates slightly higher and lower pressures. As the string oscillates back and forth, part of the string’s energy goes into compressing and expanding the surrounding air. Some sound waves can be characterized as periodic waves, which means that the atoms that make up the matter experience simple harmonic motion.Ī vibrating string produces a sound wave as illustrated in Figure 14.2, Figure 14.3, and Figure 14.4. A disturbance is anything that is moved from its state of equilibrium. More specifically, sound is defined to be a disturbance of matter that is transmitted from its source outward.
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