Moving waves can be described by their frequency, or number of waves
per second, as well as by their wavelength. If a train of waves
is moving past a stationary observer at a frequency of (nu)
complete cycles, or waves per second, and if each of these has a
(lambda) centimeters per cycle, then the wave must be moving at
a speed of
= v cm per second.
This is illustrated with boxcars and with orange light on this page
and the next.