CoachA snapshot of a periodic wave shows a pattern repeating in space; its spatial period — crest to crest — is the wavelength , in metres. A periodic wave is doubly periodic: period in time at each point, period in space at each instant.
Examples
Example 20.16 (Concert A, in air and underwater)
The concert A of Chapter 8 has wavelength in air and in water: same note, stretched by the faster medium.