Longitudinal Wave
A longitudinal wave is a wave in which the oscillation of the medium occurs parallel to the direction of wave propagation, creating alternating regions of compression (high pressure) and rarefaction (low pressure). Sound waves in air are the most common example. Because the medium must be compressed and expanded, longitudinal waves require a material medium and cannot travel through a vacuum.
Properties of Longitudinal Waves
| Property | Description | Example Value |
|---|---|---|
| Direction of oscillation | Parallel to propagation | — |
| Regions formed | Compressions and rarefactions | — |
| Medium required | Yes (mechanical wave) | — |
| Speed in air (20 °C) | ~340 m/s | 340 m/s |
| Speed in water | ~1480 m/s | 1480 m/s |
| Speed in steel | ~5960 m/s | 5960 m/s |
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Related Terms
Transverse Wave
A transverse wave is a wave in which the oscillation of the medium is perpendicular (at right angles) to the direction of wave propagation. Light waves, water surface waves, and waves on a stretched string are classic examples. Transverse waves can exhibit polarisation — a property where the oscillations are confined to a single plane — which is impossible in longitudinal waves.
Wave
A wave is a disturbance that transfers energy through a medium or through space without permanently displacing the medium itself. Waves are fundamental to how energy propagates in nature, from ocean ripples to light traveling across the universe. They are characterised by properties such as wavelength, frequency, amplitude, and speed, and underpin technologies ranging from radio communication to medical ultrasound.
Frequency
Frequency is the number of complete wave cycles that pass a fixed point per unit time, measured in hertz (Hz), where 1 Hz equals one cycle per second. It determines the pitch of a sound (higher frequency = higher pitch) and the colour of light (higher frequency = more energetic, bluer light). Frequency is inversely proportional to the wave period: f = 1/T.
From Latin "longitudo" (length), from "longus" (long). The term reflects that the wave's particle motion is along the length (direction) of propagation.