The Long Journey of a Wave
All scenes › Chapter 2 Water turns in place
Only the shape moves on
What travels is not the water but the shape of the wave and its energy
View in 3DThe shape moves on, the water stays
The yellow marker follows the crest of the wave. The crest keeps moving to the right at about 45 km/h. Meanwhile the red dot goes around once and comes back to where it started. What moves forward is not the water but the rolling shape, and the energy that makes that shape.
Why?Hold one end of a blanket and shake it up and down: a ripple runs all the way to the other end. Yet the cloth never flies out of your hands. Ocean waves work the same way.
Learn moreStrictly speaking, the water stays “almost” in place. With every turn it is nudged forward a little (Stokes drift). For a 3 m wave, that is about 0.9 m per passing wave, while the crest travels 100 m. This is one reason things floating on the sea slowly drift along.
- Speed of the crest
- 45 km/h
- Crest speed
- 12.5 m/s (45 km/h)
- How far the water is nudged per wave
- about 0.9 m
calculated from the textbook equations for water waves (linear wave theory)
View this scene in 3D →Read more
More in the series
The numbers come from the textbook equations for water waves (linear wave theory, the dispersion relation and shoaling). In the 3D view, wave heights are drawn larger; the seabed slope and the shape of breaking waves are rough sketches.