simple harmonic motion

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mathematics, physics oscillating motion (as of a pendulum) in which the acceleration of the oscillator has an equal magnitude but opposite direction to the displacement of it from the equilibrium position

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun periodic motion in which the restoring force is proportional to the displacement