Demos: 1S-40 Forced Oscillations (Resonance)

Three matched pairs of coupled pendula illustrate the phenomenon of resonance coupling.

Directions: The bar B, being suspended by strings from the upper stationary bar, causes the energy to be passed from one pendulum to another. For example, if you pull back Pendulum 3 and let it go, soon the Pendulum 6 will begin to swing, and as its amplitude grows, the amplitude of Pendulum 3 diminishes. The same will happen with pairs 2-7, 1-8 and 4-5. Other pendula will start to move also, but their motions are quickly damped out because of the phase differences.

Suggestions for Presentation: After suggesting that the pendula are coupled, ask what will happen to the others if, say, Pendulum 3 is pulled back and released. Why does only Pendulum 6 respond?

Applications: Coupled resonant systems.

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