If you have ever been talking on the phone and have idly started to bounce the
phone cord, you have probably noticed that at certain bouncing frequencies the
cord settles into a large amplitude oscillation.
With a little practice you can make oscillation patterns with one, two, three, or
even more places along the cord where the amplitude is zero.
These oscillations are called
standing waves, and they share many properties
with traveling waves.
In fact, one way to think about a standing wave is that it is two traveling waves
of the same frequency, but traveling in opposite directions.
The relation
holds for standing waves, just as it does for traveling waves.
You will need to be careful when you measure the wavelength of a standing
wave, however.
The wavelength is not the distance between the zero amplitude spots; this
distance is only one-half wavelength.
If you were to take a snapshot of the phone cord as it vibrated with
zero amplitude points only at the ends, your picture would clearly
show just a half-period of a sine wave.
So just remember that the distance between zero points in a standing wave
is one-half wavelength, and everything should work out fine (as in Lab 12, for instance).