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[Phys-l] sound waves and beam flexures



Before I embarrass myself: Beam flexure normal modes are not due to traveling sound waves. By definition sound waves are described by a second order partial differential eq., while beam flexures are by a fourth order one, yes????



e.g. banging a beam on it's end (axially) produces a sound compression wave, while banging it perpendicularly to its axis, however supported (e.g. free, free, ends pinned, ends clamped, etc.), causes flexural vibrations. Sound results just as from a vibrating speaker cone, but there is no sound in the cone (if rigid).

bc wanting the truth, praying for agreement.


p.s. for example s and p seismic waves are described by equations of the same form. The difference is the moduli (shear and Young's).