Sound is a form of energy our ears detect, originating from vibrations—rapid back-and-forth movements of an object. You can feel this energy firsthand; placing your hand on a loudspeaker playing music allows you to sense the tremors as the speaker’s surface vibrates to create sound waves.
How Sound Vibrations Are Made and Move
Every sound begins with an object vibrating, whether it is a guitar string, a drum skin, or your own vocal cords. These movements push on the surrounding particles of a medium, like air molecules. This initial push causes those particles to bump into their neighbors, creating a chain reaction of collisions.
This continuous bumping transfers energy through the medium as a wave. Individual particles do not travel with the wave; instead, they oscillate back and forth around their resting positions, passing the energy along. Sound can travel through various mediums—gases, liquids, and solids—because these states of matter have particles that can vibrate.
The speed of sound varies depending on the medium’s density and elasticity. It moves slowest through gases like air, faster through liquids such as water, and fastest through solids. For instance, a distant train might be heard sooner by pressing your ear against the tracks than by listening in the air. Sound cannot travel in a vacuum, like outer space, because no particles are present to transmit energy.
Properties of Sound Vibrations
Sound vibrations possess measurable characteristics that define what we perceive. Two primary properties are amplitude and frequency. Amplitude refers to the size or intensity of the vibration, representing how much the particles in the medium are displaced from their resting positions.
A larger amplitude means a more forceful vibration, which our ears interpret as a louder sound. This property is measured in decibels (dB), with higher decibel values indicating greater sound intensity. For example, a whisper might be around 30 dB, while a rock concert could exceed 100 dB.
Frequency describes the speed of the vibration, specifically how many complete waves pass a given point per second. This characteristic directly relates to the pitch of a sound. Faster vibrations produce higher-pitched sounds, like the high notes on a flute, while slower vibrations result in lower-pitched sounds, similar to the deep rumble of a bass drum. Frequency is measured in Hertz (Hz), where one Hertz equals one vibration per second. The human ear can perceive frequencies ranging from 20 Hz (very low pitch) to 20,000 Hz (very high pitch).
How Humans Hear Vibrations
Hearing sound vibrations involves a complex biological process within the ear. Sound waves first enter the outer ear and travel down the ear canal to the eardrum. When these vibrations reach the eardrum, a thin membrane, they cause it to vibrate.
The eardrum’s vibrations are transferred to three tiny bones in the middle ear: the malleus (hammer), incus (anvil), and stapes (stirrup). These bones amplify the vibrations before passing them to the inner ear. The amplified vibrations then reach the cochlea, a snail-shaped, fluid-filled structure within the inner ear.
Inside the cochlea, the fluid begins to move in response to the vibrations. This fluid movement stimulates thousands of microscopic hair cells lining the cochlea. These hair cells convert the mechanical vibrations into electrical signals. These electrical signals are transmitted along the auditory nerve to the brain, which interprets them as the sounds we hear, from speech to music.