Wind wave may be written as: where C is speed (in meters per second), g is the acceleration due to gravity, and d is the depth of the water (in meters). The period of a wave remains unchanged regardless of the depth of water through which it is moving. As deep-water waves enter the shallows and feel the bottom, however, their speed is reduced and their crests "bunch up," so their wavelength shortens. As waves travel from deep to shallow water, their shape alters (wave height increases, speed decreases, and length decreases as wave orbits become asymmetrical). This process is called shoaling.
Sound pressure Since formula_18, the amplitude of the specific acoustic impedance is given by Consequently, the amplitude of the particle displacement is related to that of the acoustic velocity and the sound pressure by When measuring the sound pressure created by a sound source, it is important to measure the distance from the object as well, since the sound pressure of a "spherical" sound wave decreases as 1/"r" from the centre of the sphere (and not as 1/"r", like the sound intensity): This relationship is an "inverse-proportional law". If the sound pressure "p" is measured at a distance "r" from the centre