What is Propagation speed? — Physics

Definition 20.5 High School Physics · Chapter 20 — Mechanical Waves

The propagation speed of a wave is the distance covered by the disturbance divided by the time taken: $v = d/t$ . It is the speed of the traveling shape, not of the medium.

A rope pulse photographed twice: the crest moved 2.4\, m in 0.30\, s, so v = 8.0\, m/ s — the shape travels, the rope stays. — A rope pulse photographed twice: the crest moved $2.4\,\mathrm{m}$ in $0.30\,\mathrm{s}$ , so $v = 8.0\,\mathrm{m}/\mathrm{s}$ — the shape travels, the rope stays.

Examples

Example 20.8 (Sound speeds)

Sound travels at $340\,\mathrm{m}/\mathrm{s}$ in air, $1500\,\mathrm{m}/\mathrm{s}$ in water, $5900\,\mathrm{m}/\mathrm{s}$ in steel — the stiffer, the faster. Hence the western-movie ear on the rail: steel announces the train first.

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