Longitudinal versus transverse waves

Problem

Distinguish between longitudinal and transverse waves, with a familiar example of each. Can a taut string support both? What about a steel rod?

Solution

Transverse wave. The particles of the medium oscillate perpendicular to the direction of propagation. Familiar example: the wave on a taut string when plucked; light (an electromagnetic wave) is also transverse.

Longitudinal wave. The particles oscillate parallel to the direction of propagation, creating zones of compression and rarefaction. Familiar example: sound in air.

Taut string. Mainly supports transverse waves (tension provides the transverse restoring force). It does not appreciably transmit longitudinal compression waves, because the string simply tightens/slackens.

Steel rod. Being a solid with stiffness under both compression and shear, it supports both: longitudinal waves (compression) and transverse waves (shear). This is why in earthquakes solids propagate both P waves (longitudinal) and S waves (transverse).

$\ev{\text{Long.: oscillations } \parallel \text{ propagation (sound). Transv.: } \perp \text{ (string). String} \to \text{transverse only; steel} \to \text{both.}}$

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Topics: Onde Concepts: Onda armonica Skills: Analisi di casi limite e fantafisica