Ljud

Ljud is the Swedish word for sound. In physics, sound is a mechanical wave that propagates through a medium as alternating regions of compression and rarefaction caused by a vibrating source. For a sound to be produced, there must be a vibrating body and a medium such as air, water, or solid material.

Sound waves are characterized by frequency, amplitude, and waveform. Frequency, measured in hertz, correlates with pitch; amplitude relates to loudness; the waveform determines timbre, which gives instruments and voices their distinctive color. The speed of sound depends on the medium and temperature; typical speeds are about 343 m/s in air, 1480 m/s in water, and higher in solids.

Humans perceive sound through the ear, where mechanical vibrations are transformed into neural impulses. The outer ear collects sound, the middle ear amplifies it, and the inner ear's cochlea encodes frequency and amplitude via hair cells. The auditory nerve transmits information to the brain, enabling perception of pitch, loudness, and timbre.

Sound levels are measured in decibels, using references such as 20 micropascals for SPL in air. The typical human hearing range is about 20 Hz to 20 kHz. Phenomena such as reflection, refraction, diffraction, and the Doppler effect influence how sound is heard in different environments.

Ljud has broad applications in music, speech, communication, and technology. Acoustic design reduces unwanted noise and improves intelligibility. Ultrasound uses higher frequencies for imaging and industrial inspection, while underwater acoustics supports sonar and navigation. In ecology, sound plays a key role in animal communication and habitat sensing.