Damping

When you have an old car (like many of you sixth-formers), one thing that makes it fail its MOT will be worn shock absorbers.  The latter components actually more correctly called dampers.  The springs take the shocks of falling into a pot-hole in the road.

If you are driving you old car along a road where the bumps happen to coincide with the natural frequency of the suspension, you will find your car bouncing with increasing amplitude, so that it might leave the road altogether.  Then you come to the bend...

Good dampers prevent that.

The amplitude of resonant oscillations can be reduced by damping.

• Light damping reduces oscillations slowly.

• Heavy damping reduces oscillations quickly.

• Critical damping stops the oscillation within one cycle.

The graph above shows light damping. 

Over-damped systems do not oscillate.  They take a long time to return to the equilibrium position.  An example is the return spring on a door.  The graph looks like this

  The graph below shows the effect on amplitude of damping.  The resonant frequency changes slightly.