need a science major:a glass on the table exploded tonight????

boris

Dear Boris
Thank you for showing that link. I went and read it and have a question.
The link is about how internal stresses are created when molten glass is cooled quickly in ice water, purposefully to create surface tension differences. Can internal stresses like that take place after a glass object is formed and already solid/cooled? Such as from a dishwasher's heat? The article says the stress is formed by the ice-toughened skin around the hot center glass molten, creating a tension strong enough to cause it to explode upon receiving a scratch. But there is no toughen-able skin on a factory made glass, at least I dont see how a molecular change can take place AFTER the molten stage without the foregoing being copied to the same affect DURING the manufacture, dishwashers dont get THAT hot. What do you think? (I always hated physics as its so illogical) Thanks for any basic physics common sense you can offer. The glass is so shattered on the thick base, it looks white like rock candy.

 

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milk acid

One more afterthought - could the acid in milk eat away subtly enough in a standing glass to deepen an existing scratch? I find that kinda far fetched, as glasses dont tend to get scratched on their insides, but am trying to figure out how it exploded with nothing touching it, not being handled, etc., stationary for hours. Thanks

 

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From what I can gather from other answers on other fora the stresses are in the glass from manufacture. In most cases this is no problem. In the few other cases scratches from use excerberate(sp) these defects and the glass shatters. I don't think the glass has to be toughened or have other special treatment for this to occur.

When you think of the millions of glasses made it is a wonder that it is not a more common occurance.

Why it shattered at that time...well it was most likely going to shatter at some time and that was it.

 

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Ur probably haunted. looks to me like the devil himself is in your house

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lol. Im only joking. Who knows. MAybe it was vibrations. Maybe a plane flying overhead causing the table/worktop to shake slightly but so little that u couldnt hear it. Plus if u were on the computer u would bve concentrating on something else. Table shakes ever so slightly, glass begins to move and eventually drops off end. Glass is safety glss (IMO).

 

haunted milk?

 

from what direction..

..Did an object thet struck this glass come?,if it was hit from the left,it would fall to the left,was there an open window without a screen nearby,It looks like it was hit near the base with a BB gun,there may be a hole in your screen you haven't noticed yet,but if the windows were closed that would be improbable,did you find anything on the floor in the room later on that you couldn't account for?.

 

from what i know, thers only one acid capable of etching glass. thats hydrofluric acid, which is considerably stronger than milk

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sounds like.........

an udderly frightful experience.

 

are you crazy? nobody knows the limitations of haunted milk! Haunted milk just may be the beginning of the end---for all of us! Wise-up and beware! From now on, it's black coffee for me...

 

ha ha... *pokes Unbalanced* stop with the puns....yer killing me!!

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but, here's my 2 cents worth...ahem...i'd say that the glass had had fissures and cracks that weren't visible to the human eye. and, these fissures finally lost/broke their covalent bonds and, ...well, the rest is history.

 

...as if my "Haunted Milk Theory" isn't viable...

 

Woof!!

Airdog, i'd say it's about as viable as the next guy's theory....

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This reminds me of when I was in high school. My mom was cleaning a pane of glass that went into the glass coffee table. My mom was just holding the pane, when it shattered into hundreds of pieces. Because the glass was tempered, it shattered into a bunch of tiny pieces each about a half centimeter in length. We asked my Grandpa (who used to work as a glazer) if this was common. He responded by saying that it happens quite often.

As far the thoery of tempering through dishwashing, this can not happen. Tempering can only occur at temperatures on the order of 1000 F.

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Certainly higher than the temperatures found in your dishwasher or even your kitchen oven.

The reason the temperature needs to be so high, is that there needs to be enough energy to cause the molecules within the glass the rearrange themselves and create new bonds. When the glass is quenched, this effectively "freezes" the atoms in this higher energy state. The glass as a result is harder and stronger. But on the other hand, the glass becomes more brittle.

Anyway, here's a website I found that talks about tempering glass.

http://www.alumaxbath.com/tech/tgp.htm

Inclusions in glass originate from impurities in th batch or cullet, or are combined from furnace refactories. Common forms of inclusions include aluminous stones, iron stones, and silicon. Nickel sulfide stones are uncommon, microscopic defects in glass, and may cause breakage. Delayed breakage may occur when a nickel sulfide stone is present near the center of the glass thickness.

The tempering process rarely introduces imperfections into glass. The basic glass may contain bubbles, vents, chips, and inclusions which, if accepted or not revealed by inspection before tempering can cause breakage in the initial heating or final quench operations. If inclusions are not eliminated by self destruction during the tempering process, in rare cases they may lead to failure at a later time.

 

*shakes head and puts hand over face* Oh dear!!

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In a room at school once a girl touched a window lightly with her hand and it cracked all the way up. Someone mentioned this earlier. If glass is cold enough to start with the heat from a hand is enough to cause it to crack. This doesnt seem relavent here though as no-one was near the glass of possessed milk. This theory could still be valid. Plus noones replied to my plane theory. In my opinion tiny vibrations caused the table to shake and so the glass fell off the end.Didnt have to be a place. Could have been a pneumatic drill round the corner. Anything. What is the excitement about the glass? Is it because its in little peices?? I think its safety glass.

 

Bringing up temperature change is an interesting subject. The reasons materials fail under fatigue is that the change in stresses eventually causes microcracks in the material to grow and fail. As we all know, changes in temperatures create strains in the material which could cause crack growth. So the glass will go through many temperature cycles (cold milk to hot dishwater) until the material fatigues and eventually shatters. So perhaps the cold milk in the glass was the last fatigue cycle.

As far as your plane theory, it seems implausible. The orignal poster can tell us if the glass was found on the floor or on the table. However, it seems to me that the frequency that could be transmitted to the table from an airplane would have to be low frequency. And it also seems that one would need a higher frequency to cause the table to vibrate enough to move the table.

 

i just think that the all the glass's molecule's covalent bonds broke. snapped. ka-put.

 

But why?

There has to be a catalyst to break those bonds, doesn't there?

 

bottom line: the amount of stress received caused it to break. as redundant as this may sound, the "tensile" strength wasn't strong enough, essentialy. stress=units of force divided by area.

 

That's kind of obvious though, isn't it? I mean, pretty much everything that fails by fracture, the stress was too high.

Do you think the high stress was a singular event, or perhaps an event over time such as slow crack growth due to fatigue?

 

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good lord...i think, just like everthing else in this life, those poor ol' covalent bonds got plum wore out!

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yeah, the pressure of the milk inside the glass probably caught those covalent bonds right at their weakest-linkage(

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) ) the milk was definitely in the right place at the right time, that is, if indeed that is what the milk was planning and hoping for. but, heh....who the heck knows what milk thinks these days! :bugeye: