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Water wave is an example of a 2D wave that propagates along a surface.
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Notice the bob does not travel with the wave. The motion of the wave particles are different from the “motion” of the wave.
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Each medium particle oscillate about its own equilibrium position. Their oscillatory motion result in the propagation of the energy/momentum.
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You have been taught that sound is a wave since primary school. But how do we know that sound is a wave and not a stream of particles?
