Page 193 - Schaum's Outline of Theory and Problems of Applied Physics

CHAPTER 15

Waves and Sound

WAVES

A wave is, in general, a disturbance that moves through a medium. (An exception is an electromagnetic wave,
which can travel through a vacuum. Examples are light and radio waves.) A wave carries energy, but there is no
transport of matter. In a periodic wave, pulses of the same kind follow one another in regular succession.
In a transverse wave, the particles of the medium move back and forth perpendicular to the direction of the
wave. Waves that travel down a stretched string when one end is shaken are transverse (Fig.15-1).

Fig. 15-1

In a longitudinal wave, the particles of the medium move back and forth in the same direction as the wave.
Waves that travel down a coil spring when one end is pulled out and released are longitudinal (Fig. 15-2). Sound
waves are also longitudinal.

Fig. 15-2

Water waves are a combination of longitudinal and transverse waves. Each particle near the surface moves
in a circular orbit, as shown in Fig. 15-3, so that a succession of crests and troughs occurs. At a crest, the surface
water moves in the direction of the wave; at a trough, it moves in the opposite direction. As in all types of wave
motion, there is no net movement of matter from one place to another.
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