Glass Shattering Experiment I



I decided to set up a speaker to try and shatter a wineglass with sound waves. Opening up the cupboard, I found an old wineglass with thin walls. Perfect.

To obtain the natural frequency of the wineglass I set up an amplifier and microphone, with the output of the amp connected to an oscilloscope. Placing the microphone next to the wineglass, I 'pinged' the wineglass and captured the oscilloscope waveform. The resulting waveform 'rings' at the natural frequency - just what we want!

The natural frequency for this particular wineglass was found to be ~1170 Hz. I entered this value into a frequency synthesizer program and connected a horn speaker to the output of an old 6W amplifier. Crude!

The speaker, glass, and a few other components were enclosed within an air-tight plastic box as obvious protective measures.

Initially setting the volume quite low, I used the same microphone-oscilloscope setup on the other side of the wineglass to check for resonance. At 1170 Hz, the wineglass was vibrating, but not enough. Trailing values from 1160 to 1180 Hz showed that maximum vibration occurred at 1168 Hz. I had found the exact natural frequency.

I plugged this value into the synthesizer and spun all intermediate volume control sliders to max. A video camera was set up outside the 'blast box' to capture some of the action.


Don't forget to turn up the sound! Otherwise you probably won't even know when it breaks...(The noise reduced version enables you to hear the glass shattering more easily, but the raw capture gives an idea of how loud the 1168 Hz tone is).

And here are the results... a poor old shattered wineglass. If you watched the video, you would have seen the little paper bits that jumped off the wineglass before it shattered. Those paper bits indicate magnitude of vibration, and I noticed the glass shattered soon after the vibrations were strong enough to kick the paper off.

Unfortunately, as soon as the glass fractures, it no longer resonates at the same natural frequency and doesn't 'ping' anymore, so there is no further destruction other than the possibility of smashing it on the ground.

A better view of the internal fractures in the glass. The main fracture actually extends almost right around the goblet.

It appears that shattering a wineglass is not such hardwork after all! A quick lashup was able to do the trick. But what if a bigger glass is used with a bigger amp?

Find out in the second experiment.




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