Periodic Waves
At the level of the wave medium, a wave is a displacement that is resisted by forces that have the dual tendencies of restoring equilibrium and coupling neighboring regions. The speed of the wave also depends on the mass contained in the medium because this implies inertia. Inertia governs the delay with which the energy put in at one end reaches the other end. The medium stores the energy of the wave as the potential energy of the coupling forces and as the kinetic energy of the oscillating mass. Since the mass only oscillates in place, a wave can transport energy over large distances without any mass being transported overall.
Source: Khan Academy, https://youtu.be/tJW_a6JeXD8
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