Oscillation and Periodic Motion

Definition of Oscillation—Objects in Periodic Motion

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

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

Oscillators

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 it 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. Quartz and electronic oscillators are used in modern timepieces.

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. Likewise, 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, there are no net forces acting on the object, such as the point in the pendulum swing when it is 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 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 can be described using sine and cosine functions. An example is a weight attached to a spring. When it is at rest, it is in equilibrium. If the weight is drawn down, there is a net restoring force on the mass (potential energy). When it is released, it gains momentum (kinetic energy) and keeps moving beyond the equilibrium point, gaining potential energy again (restoring force) that will drive it in oscillating down again.