Researchers discover correlation between bullet speed and number of cracks in glass

Scientists and researchers at Aix-Marseille University have conducted a study that claims there is a correlation between a bullet's speed and the number of cracks in a glass window where the bullet went through. After shooting at over 100 plexiglass plates, the researchers have concluded that the number of cracks tells us something about how fast the bullet penetrated through.

Whenever a bullet or other blunt object pierces through glass or other brittle material, the energy expands outward over the glass, creating the familiar look of radial cracking patterns formed around the bullet hole. While many people have always believed this to be completely random (and it is to an extent), it turns out that there's actually a method to the madness.

After shooting BBs at plexiglass plates, which were of various thicknesses and strengths (with the BBs traveling at different speeds), the researchers concluded and created a "global scaling law," with the rule of thumb that the number of cracks double for every fourfold increase in a bullet's (or other object's) impact speed.

These findings could be useful to forensic scientists who want to determine the location of a shooter or determine the speed of a vehicle when it got shot at. Of course, it's not something that will give you a definite answer as to how fast a bullet was traveling, but based on the researchers' findings, it's definitely something that can provide forensic investigators with an accurate estimate.

[via io9]

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