FORCED OSCILLATIONS

• Forced oscillations is when an object is force to vibrate to vibrate by another object that it is directly or indirectly in contact with. e.g. two pendulums suspended from a common string support.
• Free oscillations are not subjected to anydamping
• Resonance is the point at which energy is transfered from the forcing object to the object forced to vibrate with maximum efficiency.

GRAPHICAL ANALYSIS

amplitude		Free (undamped) oscillation, resonance occurs at natural frequency, amplitude increase for ever at resonance if energy is continually supplied. Light damping, resonance slightly below natural frequency. Heavy damping resonance below natural frequency.
	driving frequency

Note:

• Resonance has to be avoided, in machines to avoid excessive wear, when armys march over bridges (they break step).
• Resonance is useful in electric tuning circuits, in microwave ovens.