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Physics/Glass Pattern Mystery

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Question
A Very Sad Window
A Very Sad Window  
I realize that this question could go in many categories such as forensic science. I did not see that as a choice. I know that when glass breaks it follows patterns based on many things in math and physics. So I am really hoping you can help me =)

I am trying to identify the breaking pattern and probable cause in the picture. The fracture is more than 6ft from the ground on the outside. The window is a single piece of glass. I don't think it looks like a high or low velocity impact nor a thermal fracture. I don't see an impact point or radial lines. I have googled until I can't google anymore, of course nothing has look close to this...lol!!!

This is the best site I could find on the subject but it offers no pictures.

http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/jan2005/stan

Answer
Hello Danielle,

I'm afraid I don't have a good answer for you. I have delayed answering your question expecting inspiration, but none has arrived. My first thought was that a bird might have hit it. But that doesn't agree with the information on the fbi site you included. Perhaps that combined with a manufacturing anomaly could do that. There seems to be some irregularities at the left side of the arc that disagree with the description of how a heat related crack should appear. I zoomed in on your photo but it got too fuzzy to see clearly.

I don't have any expertise on this subject to apply to the problem. So I'm afraid my best answer is "I don't know what caused that."

Steve

Physics

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Steve Johnson

Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

Experience

I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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