A surfer’s kinetic energy comes directly from the waves themselves. Of all the wave forms we will study, it is with water waves that we have the most personal experience. Water waves in large bodies of water, however, have movement that is not due to the natural characteristics of waves. In pure transverse waves—like water waves—the particles of media move perpendicularly to the direction of the energy movement. If we were to create a perfect water wave in a lab, the water molecules themselves would only move up and down, while the energy of the wave would move horizontally toward the sides of the pan. In such a perfect wave, the apparent movement of water toward the side of the pan is an illusion. After completing this chapter, you will understand different types of waves, as well as their properties.
The primary topic of this chapter was wave motion. Mechanical waves are either transverse, like a swinging jump rope, or longitudinal, like a compressed slinky. Both types of waves have a wavelength, frequency, period, and wave velocity, which can be easily calculated. Waves are also subject to the Doppler effect: the apparent frequency of a wave can be lesser or greater than its actual, emitted frequency for an observer moving relative to its source, depending on the two’s relative speed and whether they are approaching or retreating from each other. This effect explains why the pitch of an emergency siren changes as it approaches a listener. Finally, this chapter explained why and how waves are refracted and reflected as they move from one medium to another.