A long swell train rolls under a pier. Cosmo picks one crest and looks at the next one behind it: the gap between them looks the same all down the train.
That repeat distance is the wave's second size number, measured along the wave instead of up from the rest line. This lesson names it.
A periodic wave repeats its shape along its length: crest, trough, crest, trough, evenly.
Pick any point on the wave, and find the next point along that looks exactly the same: the next crest after a crest, or the next trough after a trough.
From one crest to the next crest is one wavelength.
From one trough to the next trough is also one wavelength: the same repeat distance, read at a different landmark.
From a crest to the very next trough is only half a wavelength: those two points do not look the same.
Amplitude and wavelength measure different directions: amplitude reaches up from the rest line, wavelength runs along the wave.
In a snapshot of a swell train, one crest sits at the 3 m mark and the next crest at the 8 m mark. Find the wavelength.
The wavelength is the distance between two successive identical points: here, crest to next crest.
8 - 3 = 5
The wavelength is 5 m.
On the same kind of snapshot, Dilys measures from a crest top to the very next trough bottom and gets 2.5 m. Is that the wavelength?
A crest and the next trough are not identical points.
That distance is half a wavelength.
No. The 2.5 m is half a wavelength; crest to the NEXT CREST is the full 5 m.
A snapshot marks three points on a wave: J at a crest top, K at the next crest top, and L at the trough bottom between them. Which pair of points sits one wavelength apart?
In a snapshot of a wave on a creek, one crest sits at the 3 m mark and the next crest at the 9 m mark. Enter the wavelength in m.
Beata says: 'On this snapshot, the distance from one trough bottom to the next trough bottom equals one wavelength.' Is Beata correct?
Which statement defines a wave's wavelength?
A harbor camera's snapshot shows one swell crest at the 1.5 m mark and the next crest at the 5.5 m mark. Enter the wavelength in m.
Dilys measures from a crest top to the very next trough bottom along a wave and calls the distance one wavelength. Which statement about her measurement is correct?