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Q & A: spontaneously shattering glass

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Most recent answer: 05/28/2012
what could cause a glass plate that was sitting untouched on a picnic table to violently shatter into hundreds of tiny pieces? the plate had only a fork on it, and it was about 75 degrees.
- jim chaize (age 60)
rush, ny, usa
You say the "it" was about 75F. Does that mean the air temperature? If the plate itself was in the sun, part of it could have gotten much hotter. Since glass expands when it heats, there could have been big thermal strains between parts at different temperatures.

It's also true that when glass is initially formed big strains can get built in as it cools down and hardens. Sometimes glass with big strains will shatter under rather small extra strain, or just when some tiny surface crack grows enough to get the process started.

I remember when the rear window of my dad's car suddenly shattered, just sitting in the garage. Perhaps thanks to his advanced age (late 80's) he took it with equanimity: "What can you expect when something is that far out of thermal equilibrium?"

Mike W.

(published on 05/28/2012)

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