![]() Table 17.4 Speed of Sound in Various MediaĮarthquakes, essentially sound waves in Earth’s crust, are an interesting example of how the speed of sound depends on the rigidity of the medium. Because liquids and solids are relatively rigid and very difficult to compress, the speed of sound in such media is generally greater than in gases. The speed of sound in air is low, because air is compressible. This observation is analogous to the fact that the frequency of a simple harmonic motion is inversely proportional to the mass of the oscillating object. The greater the density of a medium, the slower the speed of sound. This observation is analogous to the fact that the frequency of a simple harmonic motion is directly proportional to the stiffness of the oscillating object. ![]() The more rigid (or less compressible) the medium, the faster the speed of sound. The speed of sound in a medium is determined by a combination of the medium’s rigidity (or compressibility in gases) and its density. Table 17.4 makes it apparent that the speed of sound varies greatly in different media. ![]() The relationship of the speed of sound, its frequency, and wavelength is the same as for all wavesįigure 17.9 A sound wave emanates from a source vibrating at a frequency f, f, propagates at Similar arguments hold that a large instrument creates long-wavelength sounds. So a small instrument creates short-wavelength sounds. High pitch means small wavelength, and the size of a musical instrument is directly related to the wavelengths of sound it produces. Small instruments, such as a piccolo, typically make high-pitch sounds, while large instruments, such as a tuba, typically make low-pitch sounds. The wavelength of sound is not directly sensed, but indirect evidence is found in the correlation of the size of musical instruments with their pitch. ![]() You can also directly sense the frequency of a sound. The flash of an explosion is seen well before its sound is heard, implying both that sound travels at a finite speed and that it is much slower than light. You can observe direct evidence of the speed of sound while watching a fireworks display. Sound, like all waves, travels at a certain speed and has the properties of frequency and wavelength. Sound travels more slowly than light does. Because S-waves do not pass through the liquid core, two shadow regions are produced ( Figure).Figure 17.8 When a firework explodes, the light energy is perceived before the sound energy. The time between the P- and S-waves is routinely used to determine the distance to their source, the epicenter of the earthquake. The P-wave gets progressively farther ahead of the S-wave as they travel through Earth’s crust. P-waves have speeds of 4 to 7 km/s, and S-waves range in speed from 2 to 5 km/s, both being faster in more rigid material. Both types of earthquake waves travel slower in less rigid material, such as sediments. ![]() For that reason, the speed of longitudinal or pressure waves (P-waves) in earthquakes in granite is significantly higher than the speed of transverse or shear waves (S-waves). The bulk modulus of granite is greater than its shear modulus. Earthquakes produce both longitudinal and transverse waves, and these travel at different speeds. Seismic waves, which are essentially sound waves in Earth’s crust produced by earthquakes, are an interesting example of how the speed of sound depends on the rigidity of the medium. The second shell is farther away, so the light arrives at your eyes noticeably sooner than the sound wave arrives at your ears.Īlthough sound waves in a fluid are longitudinal, sound waves in a solid travel both as longitudinal waves and transverse waves. The first shell is probably very close by, so the speed difference is not noticeable. Sound and light both travel at definite speeds, and the speed of sound is slower than the speed of light. V=\sqrt Differentiating with respect to the density, the equation becomes ![]()
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