http://www.ck12.org Chapter 12. Waves and Energy Transfer
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.