Page:Elementary lectures on electric discharges, waves and impulses, and other transients (Steinmetz 1911).djvu/23

 of a train, or a ship, etc.: here energy can be stored only as mechanical momentum, and the transient thus consists of an increase of the stored energy, during acceleration, or of a decrease, during deceleration. Thus also in a low-voltage electric circuit of negligible capacity, energy can be stored only in the magnetic field, and the transient represents an increase of the stored magnetic energy, during increase of current, or a decrease of the magnetic energy, during a decrease of current.

An instance of the second case is the pendulum, Fig. 6: with the weight at rest in maximum elevation, all the stored energy is potential  energy of gravitation. This energy changes to kinetic mechanical energy until in the lowest position, a, when all the potential gravitational energy has been either converted to kinetic mechanical energy or dissipated. Then, during the rise of the weight, that part of the energy which is not dissipated again changes to potential gravitational energy, at c, then back again to kinetic energy, at a; and in this manner the total stored energy is gradually dissipated, by a series of successive oscillations or changes between potential gravitational and kinetic mechanical