127 The Physics of Hearing

If a tree falls in a forest and no one is present to hear it, does it make a sound? This classic philosophical question highlights an important distinction between the physical and perceptual aspects of sound. From a physiological perspective, sound involves the perception of vibrations by the ear and brain. But from a physics standpoint, sound is a mechanical wave—a disturbance that travels through a medium such as air, water, or tissue, regardless of whether it is perceived.

In this sense, even if no living being is present to hear it, a falling tree still creates a disturbance in the surrounding air molecules—producing compressions and rarefactions that propagate outward as sound waves. Thus, the answer depends on your definition: if sound requires perception, then perhaps not; but if sound is defined by its physical characteristics as a wave, then yes, it occurred.

In this chapter, we will focus on both the physics of sound—how sound waves are generated and transmitted—and the biological aspects of hearing—how those waves are detected and interpreted by the auditory system. This dual perspective is especially valuable in fields such as medicine, neuroscience, and audiology, where understanding both the source of a sound and its perception is essential. We will also explore how sound waves are applied in modern medical technologies, such as ultrasound imaging and diagnostic hearing assessments.