Damping

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• When some of the energy is removed from a standing wave, the result will be a decrease in the amplitude of the oscillations.
• With light damping, the frequency of the oscillations remains relatively unchanged even as amplitude dececeases with time.
• While light damping has minimal     impact on frequency, if the oscillator has heavy damping, the oscillator will move more slowly, extending the period of oscillation and returning to the equilibrium position more quickly.
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• If an oscillator is critically damped, it will quickly  return to the equilibrium position without ever passing it. This is useful in situation where   oscillations would normally occur, but we don’t  want them to, such as in shock absorbers.
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Forced Oscillations

• A forced oscillation is when an outside, periodic force acts on a system. The effect of this regularly applied force can be dramatically different.
• If you push a swing it will move away and  back toward you with it’s natural period. If you then apply the force again at the end   of its cycle, you are creating a forced oscillation at the natural or resonant frequency of the swing. 
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• Now consider if you pushed the swing when it was ¾ of the way through its cycle. What would be the effect?
• Forced oscillations at the resonant frequency of the oscillator can dramatically increase the   amplitude of the vibrations. This is how you can shatter a wine glass with sound!
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• Forced oscillations not at the resonant frequency of the oscillator will cause vibrations, but will have limited amplitude.