Orbital motion of water particles
Topic: Movements of Ocean Water: Waves, Tides and Currents · NCERT: Class 11, Ch 13 "Movements of Ocean Water"
Meaning
When a wave passes, the water does not travel along with it. Each water particle moves in a small circle, called an orbit. As the crest comes, the water goes up and forward. As the crest passes, it goes down and back, ending close to where it started. This is why a wave carries energy, not water. The circles get smaller with depth and die out, so deep water stays still even under big waves.
Example
A fishing boat anchored off the Kerala coast simply rises and falls as waves pass under it. It does not get carried towards the shore, because the water under it only moves in circles.
Don't confuse with
- Ocean current: a real flow of water from one place to another along a set path. In orbital motion, the water only goes round in place.