This is an experiment to find the resonant frequency of a pendulum. The string is 25 cm long: it is easy to calculate its natural frequency (about 1 Hz). First, the pendulum oscillates freely. With a chronometer, you can measure its frequency (1 Hz). Then a vibrator cause a forced oscillation. The oscillator's frequency is varied from 0.7 Hz to 1.3 Hz. The amplitude reach its maximum value at 1 Hz.
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