For now, the main thing we need to know is that sine waves are connected to circular motion. To see the connection, imagine a point moving around a circle at a constant speed. If we track its up-and-down position as a function of time, the point traces out a sine wave. And because circles are intimately connected to cycles, sine waves come up wherever cyclic phenomena occur, from the cycle of the seasons to the vibrations of a tuning fork to the sixty-cycle hum of fluorescent lights and power lines.
