From Frank Fahy
Andy Howse suggests that sea waves lose energy because they have to lift the water against the force of gravity (8 August, p 25).
All mechanical waves involve an interaction between the inertia of the supporting medium and the restoring force particular to that wave; in this case, by the rise of the water surface. Waves transport energy through motion (kinetic) and energy of work done against the restoring force (potential).
At any one position, energy is continuously exchanged between these two forms as the wave passes. The storage (not loss) of potential energy as the sea surface rises is essential for wave motion to occur.
In deep water, wave energy is dissipated into heat by viscous stresses as the waves interact and water mixes, and to a small degree by turbulence in the white tops. In shallow water, energy is predominantly dissipated into heat by the friction between the wave motion and the seabed. When a wave breaks, energy is further dissipated by the viscous stresses in the turbulent flow and by work done in disturbing the seabed.
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King's Somborne, Hampshire, UK
