Simple harmonic motion is a motion that is distinguished by a direct relationship between the period of a wave and its displacement. In other words, the amount of energy put into a wave to initiate the wave is directly proportional to the displacement of the wave from its resting position. A good example of this is a pendulum, which is a weight suspended at the end of a length of rope, string, or some other attaching medium. Whatever height from the rest position you raise the weighted part of the pendulum, it will swing to an almost equivalent height across from what would be the rest position. This can also be demonstrated with a jump rope, or length of rope tied to a door knob, or some other fixed physical attribute. Stretch the rope out to its rest position, raise your hand with the rope end and snap it downward suddenly. The motion will create a simple harmonic wave that will travel the length of the rope to the door knob. More energy will create a larger wave, less energy will create a smaller wave.