Posted by Steve Simon on January 14, 2013, 1:55 pm, in reply to "Sound Polarisation"
Good question, and thank you for asking the first one.
In fluids, there is only one polarization of sound -- the longitudinal, or compressional, polarization. For these waves, the motion of the atoms is in the same direction as the direction of the wave. See the cartoon here
http://en.wikipedia.org/wiki/Longitudinal_wave
For solids, however, the motion of the atoms can be perpendicular to the motion of the wave. These are known as transverse waves. See the cartoon here
http://en.wikipedia.org/wiki/Transverse_wave
Since solids are "solid" there is a restoring force (hence a wave) corresponding to this transverse displacement. In fluids, there is no restoring force, just dissipative viscosity, so there is no real transverse wave.
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