Longitudinal Waves
Sound is a longitudinal wave: particles oscillate along the direction of propagation. Regions of compression (high pressure) and rarefaction (low pressure) move forward.
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Longitudinal Waves
Compression–rarefaction animation with direction.
Compressions and rarefactions
In a longitudinal wave, particles move back and forth along the same line as the direction of travel. Where particles are pushed together, we get a compression (high pressure); where they are spread apart, a rarefaction (low pressure). These regions move along the medium, carrying energy.
✔ Key takeaway: Longitudinal wave: compressions (high density) and rarefactions (low density) propagate in the direction of the wave.
Link to simulator: Watch the compression–rarefaction pattern and the direction arrows in the simulator.