This classic demonstration of resonance uses intense sound waves whose frequency is tuned to match the natural frequency of a glass goblet. The glass has a high lead content, which produces the high quality factor, Q, required for this demonstration. The “quality” of the glass can be heard by noting how long it rings after tapping. The natural frequency of the particular goblet to be used is carefully measured before the demonstration to within ~ 0.1 Hz. When driven by the amplifier and speaker, the standing waves excited along the circumference of the goblet take about a second to build to maximum amplitude and break the goblet.

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