Resonance Lab



RESONANCEUM Physics Demo Lab 07/2013ANALYSISNatural frequencyObjects have a preferred oscillation frequency dictated by features such as shape and material. When the wine glass is flicked by a finger, it hums at its natural frequency. When a bell is rung, it reverberates at its natural frequency. When a pendulum is released from a height, it oscillates at its natural frequency. When you accidentally drop a pan and it rings for a moment until you touch it (damping it), it is oscillating at its natural frequency. The natural frequency is a characteristic of the object.AmplitudeThe amplitude of a system’s oscillations depends on the external forces that drive it into motion. A pendulum will swing higher (have a higher amplitude) if released from a greater height since gravity will do more work on it and it will gain more kinetic energy. A bell will ring quietly or loudly depending upon how hard it is hit. And there are other ways to control the amplitude of an oscillation.Amplitude can also be increased by driving a system. A common example of a driven pendulum is a swing. If you release a swing from a height, it will swing high for a time but quickly lose amplitude until it comes to a stop at its equilibrium point. This is fun, but I’m sure you’ve all learned that you can keep the amplitude of the swing high indefinitely if you push the swing at the correct frequency, that is, every time it returns to your position during its motion. This is an example of a driven oscillator.Anytime a system is driven so that the oscillation maintains large amplitude, it is called resonance. Resonance occurs when the driving frequency is equal to the natural frequency of the system. When a system is driven at resonance, the resulting large amplitude oscillation can cause dramatic results. Rigid bells crack, bridges collapse and wine glasses shatter. Objects fail with dramatic flair when the amplitude of a driven oscillation exceeds the system’s structural limits. ................
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