Oscillation and Periodic Motion in Physics

Oscillation repeats itself in a regular cycle

High frequency sine waves on oscilloscope screen
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Oscillation refers to the repeated back and forth movement of something between two positions or states. An oscillation can be a periodic motion that repeats itself in a regular cycle, such as a sine wave—a wave with perpetual motion as in the side-to-side swing of a pendulum, or the up-and-down motion of a spring with a weight. An oscillating movement occurs around an equilibrium point or mean value. It is also known as periodic motion.

A single oscillation is a complete movement, whether up and down or side to side, over a period of time.


An oscillator is a device that exhibits motion around an equilibrium point. In a pendulum clock, there is a change from potential energy to kinetic energy with each swing. At the top of the swing, potential energy is at maximum, and that energy is converted to kinetic energy as it falls and is driven back up the other side. Now again at the top, kinetic energy has dropped to zero, and potential energy is high again, powering the return swing. The frequency of the swing is translated via gears to mark time. A pendulum will lose energy over time to friction if the clock isn't corrected by a spring. Modern timepieces use the vibrations of quartz and electronic oscillators, rather than the movement of pendulums.

Oscillating Motion

An oscillating motion in a mechanical system is swinging side to side. It can be translated into a rotary motion (turning around in a circle) by a peg-and-slot. Rotary motion can be changed to oscillating motion by the same method.

Oscillating Systems

An oscillating system is an object that moves back and forth, repeatedly returning to its initial state after a period of time. At the equilibrium point, no net forces are acting on the object. This is the point in the pendulum swing when it's in a vertical position. A constant force or a restoring force acts on the object to produce the oscillating motion.

Variables of Oscillation

  • Amplitude is the maximum displacement from the equilibrium point. If a pendulum swings one centimeter from the equilibrium point before beginning its return journey, the amplitude of oscillation is one centimeter.
  • Period is the time it takes for a complete round trip by the object, returning to its initial position. If a pendulum starts on the right and takes one second to travel all the way to the left and another second to return to the right, its period is two seconds. ​Period is usually measured in seconds.
  • Frequency is the number of cycles per unit of time. Frequency equals one divided by the period. Frequency is measured in Hertz, or cycles per second.

Simple Harmonic Motion

The motion of a simple harmonic oscillating system—when the restoring force is directly proportional to that of the displacement and acts in the direction opposite to that of displacement—can be described using sine and cosine functions. An example is a weight attached to a spring. When the weight is at rest, it's in equilibrium. If the weight is drawn down, there's a net restoring force on the mass (potential energy). When it's released, it gains momentum (kinetic energy) and keeps moving beyond the equilibrium point, gaining potential energy (restoring force) that will drive it in oscillating down again.

Sources and Further Reading

  • Fitzpatrick, Richard. "Oscillations and Waves: An Introduction," 2nd ed. Boca Raton: CRC Press, 2019. 
  • Mittal, P.K. "Oscillations, Waves and Acoustics." New Delhi, India: I.K. International Publishing House, 2010.
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Jones, Andrew Zimmerman. "Oscillation and Periodic Motion in Physics." ThoughtCo, Aug. 27, 2020, thoughtco.com/oscillation-2698995. Jones, Andrew Zimmerman. (2020, August 27). Oscillation and Periodic Motion in Physics. Retrieved from https://www.thoughtco.com/oscillation-2698995 Jones, Andrew Zimmerman. "Oscillation and Periodic Motion in Physics." ThoughtCo. https://www.thoughtco.com/oscillation-2698995 (accessed March 31, 2023).