A child sits on a swing in a playground. The swing is pulled back and released, and the child oscillates back and forth in simple harmonic motion. Explain what is meant by simple harmonic motion and describe how the amplitude and time period of the swing's oscillation change over time as air resistance acts on the system.

Simple harmonic motion is the motion of an object that oscillates repeatedly through an equilibrium position, with a restoring force that is proportional to the displacement and directed towards that equilibrium.

In the swing the restoring force is the component of gravity pulling the child back towards the lowest point.

Because air resistance dissipates energy, the amplitude of the swing gradually decreases over time.

The time period, which depends mainly on the length of the swing and gravity, remains essentially unchanged as the amplitude shrinks.

Thus the total mechanical energy of the system decreases (converted to heat), but the period stays constant.