Sound is a mechanical wave that moves via a medium. The energy of these waves generates an oscillation of pressure that move through matters and not via vacuum. It means: solid, fluid, gas or plasma. Sound waves that are audible by humans, consists of wave frequencies inside the range of normal hearing when they have sufficiently strong energy.
These waves can be detected by specific transducers that are linked to the appropriate sound systems.
In healthy humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz. As other values in medicine, such as heart rate, respirations, blood pressure, height and weight, these limits are not definite.
The upper limit generally decreases with age and ear pathology. Tinnitus sufferers usually have hearing loss, especially in the high frequencies. Human culture includes technology that is destructive to the human ear, such as loud speakers, cell phones, explosive and noisy engines.
The mechanical vibrations can be sensed as sound and have the capacity to pass via the 4 forms of materials: solid, liquid, gas and plasma, but not through vacuum.
Sound is delivered through every material that is made of molecules, such as gases, fluids solids and plasma as longitudinal waves, also called compression waves.
When sound energy is propagating via solids, however, it can be in 2 forms: (1) Longitudinal waves. (2) Transverse waves.
When the sound waves have alternating pressure deviations from the point of equilibrium pressure these are longitudinal sound waves or compression waves. At every point of equilibrium the pressure goes up (compression) and down (rarefaction).
Transverse waves are waves of alternating right and left deviations, called: shear stress. The movement is at right angle to the direction of propagation.
The mechanism of oscillation is based on the shift of the matter in the medium. It is repeatedly transposed by a sound wave, and thus oscillates. The energetic state of the sound wave when it moves back and forth is between the potential energy of the extra compression when we deal with longitudinal waves, or potential energy of lateral displacement strain when transverse waves are the issue.
In the middle, it is the kinetic energy of the matter and the kinetic energy of the oscillations of the medium.
Real (versus ideal) sound waves are complex matter waves. It is possible to apply on them the Fourier Transformation in order to receive a series of sinusoidal waves. When the aim is to understand the principle, an over simplified model can be used.
Mathematical algorithm provides a model for over simplified situation: propagation of sinusoidal plane waves. It includes 7 parameters: (1) Frequency, or its inverse. (2) Period. (3) Wavenumber. (4) Amplitude. (5) Intensity. (6) Speed. (7) Direction.
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