We are surrounded by oscillations-motions that repeat themselves. There are swinging chandeliers. boats bobbing at anchor. and the surging pistons in the engines of cars. There are oscillating guitar strings, drums, bells, iaphragms in telephones and speaker systems, and quartz crystals in ristwatches. Less evident are the oscillations of the air molecules that transmit the sensation of sound. the oscillations of the atoms in a solid that convey the sensation of temperature. and the oscillations of the electrons in the antennas of radio and TV transmitters that convey information. Oscillations in the real world are usually damped; that is, the motion dies out gradually, transferring mechanical energy to thermal nergy by the action of frictional forces. Although we cannot totally liminate such loss of mechanical energy, we can replenish the energy from some source. As an example. you know that by swinging your legs or torso you can “pump” a swing to maintain or increase the oscillations. In doing this. you transfer biochemical energy to mechanical energy of the scillating system.