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A recent article, Counting cracks in glass gives speed of projectile (Andrew Grant, Science News, May 1 2013) indicates that the number of cracks in a broken glass can tell you information about the speed of the impact that broke it.

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However, I'm not quite clear on how this is done and what the physics behind this mechanism is. Can someone explain it to me?

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closed as unclear what you're asking by Emilio Pisanty, Waffle's Crazy Peanut, David Z Sep 23 '13 at 16:40

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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The explanation can be found in the author manuscript of the article at this HAL preprint of the original journal article (Phys. Rev. Lett. 110 no. 17 (2013), 174302). It is my understanding that, for larger times, the number of cracks is determined by minimizing the sum of stretching energy and fracture energy.

You can also read the Physics Focus piece that accompanies the journal article.

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