How high a frequency does it take to break a wine glass?

Stian Mork

 

Stian Mork &
Eirin Holmstrøm

The other day Stian was asked “how high a frequency does it take to break a wineglass?”, and he didn’t have an answer, but this question piqued his curiosity. So, together we turned to SOLIDWORKS Simulation and took a closer look at the different tools they provide to see if one of them could help us find out just how high the sound had to be to break the glass.

Sound and frequency

Before we start analyzing, we need to understand exactly what it is that makes the wine glass break. As you may know sound consists of waves of energy. At different sound levels we also have different frequencies. Frequency = the number of oscillations in a sound wave per second.

In the same manner all structures have their own resonant frequencies. This means that structures have certain frequencies that make them fluctuate in the same manner that a sound wave fluctuates. An example from real life is the Tacoma Narrows Bridge, also known as Galloping Gertie. When designing the bridge, they had forgotten to take into account that the structure itself could start to resonate due to the gusts of wind that hit it, and this had catastrophic consequences.

What actually makes the glass break is the fact that it starts to oscillate together with the frequency of the sound wave that hits the glass, in the same way the Tacoma Narrows Bridge did when hit by the wind. This means it’s not just a matter of how loud the sound is (above 100db), but more importantly what frequency the sound has (low><high).

A 3D scan of the wine glass

We wanted to run a frequency analysis in SOLIDWORKS Simulation Professional in order to find out what sound we needed to “overload” the wine glass within order to break it. In order to do that we needed to make a 3D model of the wine glass. We had one of our colleagues do a 3D scan where the glass got transformed from a physical model to a 3D model, and of course we made sure to use a glass that was guaranteed to break.

Frequency analysis in SOLIDWORKS Simulation

We opened the scanned 3D model in SOLIDWORKS.
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From the list of studies, we chose “Frequency study”. By using the frequency study found in SOLIDWORKS Simulation Professional we can easily find frequencies for both parts and assemblies.
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We chose glass as type of material (retrieved from the standard database in SOLIDWORKS),
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and fixed the bottom of the wine glass to an imaginary table. This means that we would also have to somehow lock the bottom of the glass 100% tightly to a table when making a physical test for the two tests to coincide.
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After having studied just how the wine glass moves before it breaks, we concluded that what we were looking for was the first frequency that causes the upper part of the glass to fluctuate in a diagonal manner.

Glassbreak(Youtube_Marty33)
YouTube: Wine glass resonance in slow motion

All structures have an infinite number of resonant frequencies, but since we were unsure where the frequency shown in the video above occurs, we decided to try out the ten lowest resonant frequencies of the wine glass.
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We discovered that the oscillations that occurred at the lowest frequencies were due to the glass oscillating sideways around the trunk, but this was not the frequency we were looking for and that would cause the glass to break.
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At frequency mode 4 (500Hz) exciting things started to happen. When animating the vibration here, we saw that this coincides with the video shown before. In other words, if we create a sound frequency of 500Hz together with a sound level of over 100dB, then this glass will in theory break and the myth thus confirmed.
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Frequency analysis, like the one used in this example, is part of SOLIDWORKS Simulation Professional. On our product pages you can find more information about the different solutions we can provide within SOLIDWORKS Simulation and find more information on how they enable you to test your product.

If you have any questions concerning Simulation don’t hesitate to ask, you’re always more than welcome to reach out – we’re just a click away.