17.1:
Sound Waves
Sound is a mechanical wave generated by the vibration of an object and requires a medium to propagate.
Whereas hearing is the ability to perceive sound waves by detecting the vibrations in the surrounding medium.
Sound waves cause the particles of the medium to vibrate and transport energy through it. Since the wave propagates parallel to the direction of the vibrations, sound waves are referred to as longitudinal waves.
During vibration, the particles move back and forth, resulting in high-pressure and low-pressure regions in the medium known as compressions and rarefactions, respectively.
In space, sound waves cannot travel since there are no particles to vibrate and propagate the sound wave.
Since sound is a pressure wave, it can be modeled similarly to periodic wave equations. When propagating in the air, sound waves can also be modeled in terms of the displacement of air molecules.
17.1:
Sound Waves
Sound waves can be thought of as fluctuations in the pressure of a medium through which they propagate. Since the pressure also makes the medium's particles vibrate along its direction of motion, the waves can be modeled as the displacement of the medium's particles from their mean position.
Sound waves are longitudinal in most fluids because fluids cannot sustain any lateral pressure. In solids, however, shear forces help in propagating the disturbance in the lateral direction as well. Hence, in solids, sound waves are both longitudinal and transverse.
The medium absorbs a fraction of the energy propagated through the sound wave due to its viscosity. In each compression, a fraction of the energy is converted as heat, and in each rarefaction, a smaller amount of this returns to the wave. Hence, with time, a wave propagating through a medium loses its energy as random thermal energy to the surrounding medium.
The human ears collect sound waves in the air and channel them to the brain, which creates the perception of hearing. They are sensitive to a gamut of sound wave frequencies, from about 20 Hz to 20,000 Hz. This range is called the audible range.
This text is adapted from Openstax, University Physics Volume 1, Section 17.1: Sound Waves.