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Lesson: Chapter 4 — Waves and their applications

4.1.1. Transverse waves 2 of 3

Crests and troughs

At any instant a transverse wave has high points and low points. The highest are its crests; the lowest its troughs.

Figure to be added

Figure 4.7 — a cross-section of a water wave at one instant, with crests at A and B and troughs at C and D; small arrows show which way the water particles are moving at that moment.

Crest

The particles at A and B have moved the greatest possible distance upwards. Positions like these are the crests of the wave.

Trough

The particles at C and D have moved the greatest possible distance downwards. Positions like these are the troughs of the wave.

Crests and troughs do not travel with the water

A crest is a position, not a lump of water. The water under a crest moves back down a moment later, and the crest appears one step further along — made of different water.