Sounds

Sound is a mechanical wave produced by vibrating objects and propagating through a medium as pressure variations. In gases, liquids, and solids the disturbance travels as longitudinal waves, with regions of compression and rarefaction carried by the particles of the medium. Sound requires a medium to propagate; it does not travel in a vacuum.

The primary physical properties of sound are frequency, amplitude, and timbre. Frequency, measured in hertz, determines pitch; higher frequencies produce higher pitches. Amplitude relates to loudness and is commonly expressed as sound pressure level in decibels. Timbre, or tone color, distinguishes different sound sources even when they share the same pitch and loudness. The speed of sound depends on the medium and its conditions: for air at room temperature it is about 343 meters per second, faster in liquids and even faster in solids. Wavelength is the distance over which the wave’s shape repeats and is the product of speed and period.

Perception of sound involves the auditory system. Humans typically hear from about 20 Hz to 20 kHz, with sensitivity varying across frequencies and decreasing with age. The ear converts mechanical energy into neural signals via the outer ear, middle ear (ossicles), and inner ear (cochlea). The decibel scale measures sound intensity, with weighting curves like A-weighting reflecting human sensitivity. Excessive exposure can cause hearing damage.

Sound interacts with environments through reflection, absorption, diffraction, and interference, producing phenomena such as echoes and reverberation. It can be natural or human-made, including speech, music, noise, and ultrasonic or infrasonic signals. Applications span acoustics, audio engineering, ultrasound imaging, sonar, and architectural design, while health and safety considerations focus on noise control and hearing protection.