 The wave account is, of course, endorsed by modern acoustics. Sounds are construed as mechanical vibrations transmitted by an elastic medium. They are thus described as longitudinal waves, defined by their frequency and amplitude. A vibrating object (the sound source, such as a moving vocal chord or a vibrating tuning fork) creates a disturbance in the surrounding medium (say, air, or water). Each particle of the medium is set in back-and-forth motion at a given frequency and with a given amplitude, and the motion propagates to neighboring particles at the same frequency, undergoing an energy loss that entails a decrease in amplitude. Seen macroscopically, the propagation of sound is the propagation of a compression in the medium followed by a depression, that is, the propagation of a wave. The behavior of each particle is described by a sinusoid that maps the cyclical pattern of compressions and depressions against time. A cycle is the complete path of the sinusoid from crease to crease, at the end of which the particle is back to its starting position. Amplitude is the distance between creases and valleys in the sinusoid, period is the distance between a crease and its successor, and frequency is the number of cycles per time unit.