An example of a wave with both longitudinal
and transverse motion may be found in solids as a Rayleigh surface
wave. The particles in a solid, through which a Rayleigh surface
wave passes, move in elliptical paths, with the major axis of
the ellipse perpendicular to the surface of the solid. As the
depth into the solid increases the "width" of the elliptical
path decreases. Rayleigh waves are different from water waves
in one important way. In a water wave all particles travel in
clockwise circles. However, in a Rayleigh surface wave, particles
at the surface trace out a counter-clockwise ellipse, while particles
at a depth of more than 1/5th of a wavelength trace out clockwise
ellispes. This movie shows a Rayleigh wave travelling from left
to right along the surface of a solid. Two particles are identified
in yellow to illustrate
the counterclockwise-clockwise motion as a function of depth.
Text & movie taken from Professor Dan Russell's Vibration & Waves Animation webpage. Visit this page for many excellent visualization tools for acoustics and vibration.
The (0,3) mode of a circular membrane, shown
at right, has three circular nodes, but no diameter nodes. The
frequency of the (0,3) mode is 3.598 times
the frequency of the (0,1) mode. Like the (0,1) and (0,2) modes,
the (0,3) mode is excited when the membrane is struck at the
center. The sound radiation characteristics of the (0,3) mode
are rather complicated. This mode is excited when the membrane
is struck at the center, and it dies away fairly quickly. As
a result, it contributes to the "thump" sound when
a drum is hit at the center, but does not contribute much to
the musical
pitch of a drum when hit off center.
Text & movie taken from Professor Dan Russell's Vibration & Waves Animation webpage. Visit this page for many excellent visualization tools for acoustics and vibration.
