(Updated on 17/3/2013, Tues):
a. A body oscillating freely at its natural frequency but with decreasing amplitude is said to experience damping:
b. Damping occurs in an oscillating system when the system loses energy resulting in the decrease in amplitude but not the frequency of the oscillation.
c. Examples: A pendulum swinging freely or a loaded spring oscillating freely in a non-vacuum environment will see the amplitude of its swing or oscillation gradually decreases (while the frequency remains unchanged) until the swinging or oscillation stops.
d. When damping occurs, energy is lost in 2 possible ways:
i. To overcome frictional forces or air resistance – External damping;
ii. Due to the extension or compression of the vibrating particles – Internal damping.
e. To overcome damping, external force must be applied (thus energy is supplied) to keep the amplitude from decreasing. Such an oscillation is called forced oscillation.