Circles in the Water

Energy moves, water doesn’t

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Water particles move in circles as a wave passes; energy travels, water doesn’t.
• The motion dies out by about half a wavelength down.
• Water counts as “deep” when depth exceeds half the wavelength.
• Deep-water period: $T = \sqrt{2\pi\lambda/g}$.

Steps

1. Bobbing, not travelling
2. Deep down
3. Watch the water
4. A quarter-wavelength down
5. Riding out a storm
6. Swell timing