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Counting cracks in glass gives speed of projectile

published by Science News
May 08, 2013

The number of cracks that emerge in a plate of glass or Plexiglas relates to the speed of the object that broke it, researchers demonstrate April 26 in Physical Review Letters. This simple relationship could prove useful for forensic scientists, archaeologists and even astronomers.

The study's approach is clever, says Alan Zehnder, a mechanical engineer at Cornell University. But he points out that most impacts do not lead to such orderly, star-shaped crack patterns. He also notes that Vandenberghe's materials were on a smaller scale than most everyday examples: The plates in the experiment are much thinner than a typical windowpane, he says, and the steel balls were significantly smaller than rocks that shatter windshields.