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Longitudinal and Transverse

Waves can be categorized as either longitudinal or transverse - it’s all down to how the wave moves. The sound waves produced by a guitar cause air particles to oscillate parallel to the direction of wave propagation. This is an example of a longitudinal wave. In contrast, the waves produced by the rippling surface of a pond cause water particles to oscillate perpendicular to the direction of wave propagation. They are transverse waves.

Depicted is the difference between longitudinal and transverse waves. Two waves are shown, one above the other, both propagating to the right. The first is a longitudinal wave produced by a source that is oscillating from left to right. The positions of the particles in the medium are depicted with blue vertical lines producing a repeating pattern of low and high density regions. A single particle is shown in red oscillating from left to right, parallel to the direction of propagation. The second wave is a transverse wave produced by a source oscillating up and down. The displacement of the particles in the medium forms a sine curve shape with repeating peaks and troughs, depicted by a blue line. The particles oscillate up and down, perpendicular to the direction of propagation. This is highlighted with a red arrow for a single particle. Several other particles are shown in red at their current displacement. The peaks of the transverse wave correspond to the points with maximum density in the longitudinal wave.

Figure 1: Diagram showing the difference between longitudinal and transverse waves.