Demos: 1S-25 Resonance Bar Pendula

Resonance and exchange of energy between a pair of coupled pendula is demonstrated. Two identical bars, freely suspended, are coupled by a light spring. If one of the bars is set into oscillation, energy is transferred to the other, causing the latter to increase its amplitude of oscillation while the former decreases its amplitude. Eventually, the situation reverses and the initial conditions reappear.

Directions: With the system starting at rest, pull sideways on one of the bars and release.

Suggestions for Presentation: Since the two bars are identical, focus on the idea that they have the same resonant frequency. Then bring out the concept that energy is most efficiently transmitted when the two systems are in resonance with each other. Ask what will happen when one bar starts to oscillate. Why does the amplitude of one decrease while the other increases?

Applications: Any system that is coupled and the resonant frequencies are near the same.

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