In order to successfully perform this impressive demonstration of mechanical resonance the natural resonance frequency of the object has to be predetermined . After striking the glass placed in the sound chamber with a rubber mallet the characteristic peak frequency is identified from the FFT computer recording (Data Studio, Beaker Breaker 1). The strobe light is set to slightly above or below ?resonance frequency x 60? flashes/minute. The low volume output from the function generator (which feeds the oscillator through the power amplifier and horn driver) is slowly swept through the frequency region near the expected resonance. When the driving acoustic signal approaches the glass natural resonance frequency, the sudden increase in amplitude of sound generated by the vibrating glass can be observed (Data Studio, Beaker Breaker 2). The astounding oscillations of the object can be noticed also as the strip of paper placed on the glass rim jumps and moves around the rim perimeter. The relative 90 deg phase difference between the driving voltage from signal generator and the sound produced by vibrating glass (microphone output) indicates the exact resonance state. When at resonance a quick jolt of the driving signal (function generator output to half of its max, power amplifier up to ? 15 dB) results in shattering the glass. Caution: exceeding the output signals above the suggested values will result in blowing the security fuse or burning the speaker voice coil. For best outcome the object should be carefully selected (high Q), cleaned right before the demonstration, positioned at a distance of about 0.5 cm from the mouth of the driver and fastened to the jack with thin double stick cellophane tape. The microphone position has to be adjusted to about 1 cm from the glass wall. The stroboscope rate will also require some very subtle adjustment after the resonance is found to assure nice and slow apparent vibration of the object at the beat frequency.

Sound sensor to analog Channel A. Voltage probe (connected to the signal generator output) to analog Channel B.

File 1: Beaker Breaker 1. Used to detect the natural resonance frequency of the object to be shattered. For sound sensor Med Sensitivity (x10) is selected. FFT display (1024 point) with relative amplitude of mic signal vs. frequency (range 0 ? 1200 Hz, can be extended if necessary). Sampling at 2500 samples/sec, automatic stop time at 1 sec. Replace matching measurements selected. Summary window closed. Bold trace. To identify the resonance frequency the X-Y tool is used.

File 2: Beaker Breaker 2. Used to show the phase shift between the driving signal and the sound of the resonating object and to identify precisely the moment of resonance (the instant to increase the power of the driving signal). Simultaneously it allows to observe the increase in amplitude of the sound generated by resonating glass. For both sensors Low Sensitivity (x 1) is selected, no options, sampling at 50000 samples/sec. Two scope displays selected in a tile window arrangement. Summary window closed. Scope 1 shows microphone vs. driving voltage trace in bold, 2 Volts/div for both axes, 0 offset. Trigger on, triggering voltage =0 and rising. Scope 2 displays microphone (5 Volts/div) and driving force (2 Volts/div) vs. time (0.5 ms/div). 0 offset. Trigger on, triggering voltage 0 and rising.

Suggestion

1. Showing circular standing waves on hand driven metal hoops could make a nice introduction to this demo.
2. This presentation can be followed by the teacup standing waves demo (3D40.50).