1.4: Forced Oscillations and Resonance
How do you keep an oscillation going while it loses energy due to friction? You need to replenish the lost energy by doing work. For example, a wristwatch uses the period of a vibrating quartz crystal to keep time, but the crystal can only maintain that vibration with the help of a battery.
When an oscillator receives external energy, that is called a forced oscillation. A surprising effect arises when you try to supply the energy with an external driving force that is itself periodic. The rate that energy can be transferred to a harmonic oscillator maximizes if the periodicity of the driving force matches the period that the oscillator would move if left alone – its natural period.
Read this text which explains how a dramatic increase in the oscillation amplitude as the driving period is adjusted can lead to resonance. Notice the frequency where the driven oscillation occurs. Is it the natural frequency of the oscillator, or is it the frequency with which the external force is applied? If you try the experiment in Figure 16.26, you will see that you control the frequency – not the paddle ball. However, the response of the oscillation amplitude depends dramatically on which frequency you choose.