
120 Questioning the Universe: Concepts in Physics
Because of the unique relation of the speed of a wave and its medium, many times
the speed of a wave is quoted without referencing it to some frame. In that case,
what is meant is the speed of the wave relative to its own medium (i.e., the speed as
measured by an observer at rest in the medium). So, if someone states that the speed
of sound is 1,000 ft/s, what is meant is that, relative to the air, the speed of sound is
1,000 ft/s. Of course, if an observer is moving toward the source of the sound at, say,
100 ft/s, then that observer would measure a speed of 1,100 ft/s.
We should note here t ...