Properties of progressive waves

The properties of a progressive wave -- already established in Class XI, so only briefly recapped here as they will be used repeatedly through this chapter -- are: every particle of the medium executes the SAME type of vibration (simple harmonic motion about its own mean position); all particles share a common amplitude, period and frequency; the PHASE (state of vibration) changes continuously from one particle to the next along the direction of travel; no particle stays permanently at rest, each one only momentarily pausing at its own extreme positions; particles move fastest exactly as they pass through their mean positions; energy is carried along the wave without any net transfer of matter; the wave's own propagation speed through a medium depends only on the properties of that medium; and progressive waves are of the two familiar kinds, transverse and longitudinal, with mechanical waves of BOTH kinds able to propagat …