1.7: Energy in Waves
All waves carry energy. We can see the destructive forces waves cause in many ways: earthquakes, ocean waves that cause erosion, and musicians who have hearing loss due to the sound waves that pound the nerve cells in their inner ears. However, we have also learned to harness the energy of waves, such as when physical therapists provide deep-heat ultrasound treatment to muscle strains or when surgeons use laser beams to burn away cancer cells.
Read this text to learn more about energy in waves. The amount of energy in a wave is related to its amplitude. When we talk about the amplitude of a wave, we refer to deviations from the equilibrium of the medium carrying the wave. Large-amplitude earthquakes produce large ground displacements. Loud sounds have higher pressure amplitudes and come from larger amplitude source vibrations than soft sounds. Large ocean breakers churn up the shore more than small ones.
At the level of the wave medium, a wave is a displacement that is resisted by forces that have the dual tendencies of restoring equilibrium and coupling neighboring regions. The speed of the wave also depends on the mass contained in the medium because this implies inertia. Inertia governs the delay with which the energy put in at one end reaches the other end. The medium stores the energy of the wave as the potential energy of the coupling forces and as the kinetic energy of the oscillating mass. Since the mass only oscillates in place, a wave can transport energy over large distances without any mass being transported overall.