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Every wave -- whatever its type -- can be described by a common set of quantities: amplitude (A), the largest displacement any particle of the medium undergoes from its rest position; wavelength (λ), the distance between two successive particles that are in exactly the same phase of vibration; period (T), the time for one particle to complete a full vibration; frequency (n = 1/T), the number of vibrations per second; and wave velocity (v), the distance the disturbance itself advances per unit time. Because a wave covers exactly one wavelength in exactly one period, these combine into the single most-used relation of wave motion, $v=n\lambda$. …