![]() ![]() 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. The greater the density of a medium, the slower the speed of sound. 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. The speed of sound varies greatly depending upon the medium it is traveling through. Through this discussion, develop the concept that the speed of sound is finite and measurable and is much slower than that of light. This phenomenon is also observed during a display of fireworks. Ask them why the sound of thunder is heard much after the lightning is seen during storms. Ask students if they know the speed of sound and if not, ask them to take a guess. Review the fact that sound is a mechanical wave and requires a medium through which it is transmitted. Just as a transverse wave alternates between peaks and troughs, a longitudinal wave alternates between compression and rarefaction. ![]() 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. Review properties of waves-amplitude, period, frequency, velocity and their inter-relations. Review waves and types of waves-mechanical and non-mechanical, transverse and longitudinal, pulse and periodic. (B) investigate and analyze characteristics of waves, including velocity, frequency, amplitude, and wavelength, and calculate using the relationship between wave speed, frequency, and wavelength.In addition, the High School Physics Laboratory Manual addresses content in this section in the lab titled: Waves, as well as the following standards: (F) describe the role of wave characteristics and behaviors in medical and industrial applications.(C) compare characteristics and behaviors of transverse waves, including electromagnetic waves and the electromagnetic spectrum, and characteristics and behaviors of longitudinal waves, including sound waves.(A) examine and describe oscillatory motion and wave propagation in various types of media.The student knows the characteristics and behavior of waves. The learning objectives in this section will help your students master the following standards: ![]()
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