1.3: Oscillations and Energy
There is a continual exchange between kinetic and potential energy during any oscillation, as the system speeds up near equilibrium and slows down before it turns around. This is just as true for a playground swing as for a vibrating tuning fork. Since the concept of energy permeates all of physics from classical mechanics to electromagnetism and beyond, it is useful to describe oscillations in this vocabulary.
The total energy of an oscillation is determined at the moment you get it going. In an ideal simple harmonic oscillation, this total remains constant even as kinetic and potential energy individually change in synchrony with the motion. But, as you know from experience, oscillations do not usually last forever; they peter out because of friction, air resistance, or other forces. In this case, we speak of a damped oscillation instead of a harmonic oscillation.
In terms of energy, damped oscillations cannot maintain a constant balance of kinetic and potential energy because some of the mechanical energy is drained away in the form of thermal energy. This eventually causes the mechanical motion of the oscillator to return to equilibrium and stay there. At that point, all the energy of the oscillation has been converted to microscopic, invisible motion at the molecular level in the surrounding air or the oscillator itself.