AQA A-Level Physics/Forced Vibrations, Damping and Resonance
Forced Vibrations and Resonance- Free vibrations are where the total energy stays the same over time. This means that the amplitude of the vibrations remain the same. This is a theoretical idea because in the real systems the energy is dissipated to the surroundings over time and the amplitude decays to 0. This dissipation is called dampening.
Forced vibrations occur when the object is forced to vibrate at a particular frequency by a periodic input of force. Objects which are free to vibrate will have one or more natural frequencies at which they vibrate. These are the frequencies that the object will vibrate at when left for a time, and they natural reach these frequencies. If an object is being forced to vibrate at its natural frequency, resonance occurs and you will generate very large amplitude vibrations.
The effect of damping on resonance graph: The amplitude of the resonance peak decreases and the peak occurs at a lower frequency. So damping lowers the natural frequency of an object and also decreases the magnitude of the amplitude of the wave.
Phase and resonance: The phase relationship between the driving oscillation and the oscillation of the object being driven is different at different frequencies. -Below resonance they are in phase with each other
-At resonance the phase relationship is 90 degrees
-Above resonance the phase relationship is 180 degrees.