Webster's dictionary defines a wave as shown in Figure
.
The most
important part of this definition is that a wave is a "disturbance or
variation" that travels through a medium. The medium through which the
wave travels may experience some local oscillations as the wave passes, but the
particles in the medium do not travel with the wave. The disturbance may take
any of a number of shapes, from a finite width pulse to an infinitely long sine
wave.
At many sporting events, fans will perform an activity referred to
as the wave. The wave is formed by a group of people jumping up and sitting
back down. Some nearby people see them and they jump up, some people further
away do the same thing and soon there is a wave traveling around the stadium.
The wave, or the action of people jumping up and sitting back down, is the
disturbance, and it travels around the stadium. However, none of the individual
people in the stadium are carried around with the wave as it travels. They all
remain at their seats.
Longitudinal sound waves in the air behave in
much the same way. As the sound wave passes through, the particles in the air
oscillate back and forth from their equilibrium positions but it is the
disturbance that travels, not the individual particles in the medium. The first
interactive activity illustrates this concept.
Transverse waves on a string are another example. The string is displaced up
and down, as the wave travels from left to right, but the string itself does
not experience any net motion. This is shown in the second interactive
activity.