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Sound is a mechanical wave generated by vibrating objects that requires a medium to propagate, while hearing is the ability to perceive sound waves by detecting vibrations in the surrounding medium. The human ears collect sound waves and channel them to the brain, which creates the perception of hearing. Hearing sensitivity ranges from about 20 Hz to 20,000 Hz, known as the audible range.

Sound waves are longitudinal because they propagate parallel to the direction of particle vibrations. As particles move back and forth, they create high-pressure regions called compressions and low-pressure regions called rarefactions. Since sound is a pressure wave, it can be modeled as displacement of medium particles from their mean position.

During vibration, particles of the medium move back and forth, creating alternating regions of high and low pressure. Compressions are high-pressure regions where particles are pushed together, while rarefactions are low-pressure regions where particles spread apart. These pressure fluctuations propagate through the medium as the sound wave travels.

Sound waves cannot travel through space because there are no particles present to vibrate and propagate the wave. Since sound is a mechanical wave that requires a medium to transport energy, the absence of particles in the vacuum of space prevents sound propagation entirely.

In fluids, sound waves are purely longitudinal because fluids cannot sustain lateral pressure. In solids, however, shear forces enable propagation in the lateral direction as well, making sound waves both longitudinal and transverse. This fundamental difference arises from the structural properties of each medium type.

As sound waves propagate, the medium absorbs a fraction of the energy due to its viscosity. During each compression, energy converts to heat, and during rarefaction, only a smaller amount returns to the wave. Over time, the wave loses energy as random thermal energy to the surrounding medium.

Sound waves can be modeled using periodic wave equations since they are pressure waves. When propagating in air, sound waves can also be modeled in terms of displacement of air molecules from their equilibrium positions. Both approaches—pressure fluctuation and particle displacement—provide valid mathematical representations of sound wave behavior.