Excited pendulum 
This applet deals with the case of a simple pendulum that is excited by a hammer that hits the pendulum ball with a constant frequency (controlled by the user). It is possible to verify that, when the period of the hammer is, for example, approximately equal to the period of the pendulum (without blows), a resonance phenomenon begins.
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Translated for Atractor by Gabriela Chaves, from its original version in Portuguese. Atractor is grateful for her cooperation.
