Chapter 12— THE GOVERNING FUNDAMENTALS OF METEOROLOGY 



Source 



WAVES 



Any object that moves rapidly to and fro, or 

 vibrates and thus disturbs the medium around 

 it, may become a sound source. Bells, radio 

 loudspeaker diaphragms, and stringed instru- 

 ments are familiar sound sources. 



Medium 



Sound waves are passed along by particles 

 of the material through which they travel. The 

 elasticity of the medium determines the ease, 

 distance, and speed of sound transmission. The 

 greater the elasticity, the greater the speed of 

 sound. The speed of sound in water is about 

 four times that in air, for example; in steel, 

 it is about 15 times greater than in air. 



Detector 



The detector acts as the receiver of the 

 sound wave. Because it does not surround the 

 source of the sound wave, the detector absorbs 

 only part of the wave's energy, thereby usually 

 requiring an amplifier to boost the signal's 

 energy • to permit reception of weak signals. 



Waves may be classified by types as trans- 

 verse and longitudinal. A transverse wave is 

 one wherein the particles of the medium through 

 which the wave is passing move at right angles 

 to the wave's direction. In a longitudinal wave, 

 the particles move back and forth along the 

 wave's direction of travel, resulting in com- 

 pression and rarefaction of the wave. An 

 example of a transverse wave is a water wave. 

 An example of a longitudinal wave is a sound 

 wave. Both types can be illustrated with a 

 spring as shown in figure 12-22. 



Characteristics of transverse and longitudi- 

 nal waves are illustrated in figure 12-23. 



In the figure, the circles show the equilib- 

 rium positions of the particles in the medium; 

 the dots show their displaced positions; the 

 arrows indicate the displacement of the 

 particles from their equilibrium positions. Note 

 that in the transverse wave, the particles move 

 at right angles to the direction of wave move- 

 ment; in the longitudinal wave, the particles 

 move parallel to the direction of wave move- 

 ment. Wavelength, which was defined earlier 

 in the chapter, is illustrated by the distance 

 between positions a and b. Amplitude, which is 



CREST 



TRANSVERSE WAVES IN A SPRING 



COMPRESSION RAREFACTION 



-A- 



LONGITUDINAL WAVES IN A SPRING 



Figure 12-22. — Comparison of transverse and longitudinal waves. 



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