A perfectly good glass bottle can be broken by the force exerted by collapsing bubbles. A team of BYU fluid dynamics graduate students took the time to figure out how. Credit: Adapted from BYU video.

Peter has been keeping you apprised of the emergence of the Usable Glass Strength Coalition, a collaboration focused on precompetitive basic research to improve glass properties. The coalition’s inaugural meeting of its board of directors took place just last week, here at ACerS HQ. Peter will report more about the meeting, but with the coalition’s birth as background, this video of a bottle breaking caught my eye.

As a materials scientist, my first thought when a material fails—and perhaps yours, too—is to ask what weakness in the material led to the failure? That might not necessarily be the right question to ask, though.

A paper posted on arXiv.org last October (more like an extended abstract), offers proof that what is in the bottle affects how easy it is to break the bottle.

Apparently, a favorite party trick is to break a glass bottle by filling it with water and then slamming the top with an open hand. Rather dramatically (as the video shows), the bottom of the bottle cracks, and water and glass spew forth. (I have never seen this party trick, evidence that I need to get out more, perhaps.)

The trick does not work with fizzy liquids, nor with an empty bottle, which got a curious group of fluid dynamics graduate students—Jesse Dailey, Ken Langley, Scott Thomson, and Thad Truscott—at Brigham Young University in Provo, Utah asking, why?

The three minute video is fun to watch, with high speed video showing how the bubbles form, and they insert good explanation slides along the way.

Here is a breakdown of what happens.

  • The hand slap exerts a downward acceleration on the bottle, which …
  • Creates a low pressure region in the fluid at the bottom of the bottle, which …
  • Causes bubbles if the low pressure formed is less than the vapor pressure of the fluid. This bubble formation is known in the fluid dynamics world as “cavitation.”
  • The bubbles collapse when the pressure returns to normal, but …
  • The collapse happens ten-times faster than it takes to form the bubbles in the first place, which …
  • Produces instantaneous, concentrated forces much greater than those caused by the initial acceleration with the hand slap.
  • The bottle breaks.

The reason it does not work with fizzy fluids is that the cavities fill with carbon dioxide and float away instead of collapsing.

The group applies rigorous science and experimental techniques to arrive at their conclusions. They use an accelerometer and high speed videography to confirm that the strike to the bottle and the catastrophic crack are not simultaneous. The video clearly shows the burst happening after the bubbles collapse. The team also pulls out some fancy fluid dynamics equations to further explain their conclusions.

So, the point for failure analysis experts and bottling plant engineers to keep in mind is that, sometimes, there really is nothing wrong with the material!