How does glass crack without breaking?

Question

Scenario 1: You can put pressure on a certain part of a glass frame and you will see white cracks appear. They seem to go all the way through, and yet it remains intact.

Scenario 2: Someone hits a reinforced window with a baseball bat. The cracks appear to go all the way through, and it doesn't break. Why is that?

I suspect it's to do with the molecular structure of glass.

While I'm at it, I'll just illegally bombard you with questions.
1. Exactly what is glass?
2. What makes some glass bulletproof?
3. What is it with high-pitched noises being able to shatter glass?
4. Is it possible to make a noise of such frequency that glass won't just break into smaller fragments, but actually disintegrate? The smaller the fragments, the harder they are to break, right? But could a noise be of such a pitch or force that they break into molecules so small they can't be seen?
5. And of course, my original question. How does glass crack without breaking?

Answer 1

So your later questions first seems best:

#1. I believe its Silicon Dioxide... primarily. Its unlikely to be pure though. There will be other things in there. Oh, and it could be said by many to be a liquid... because it flows... though since it takes centuries to go anywhere, I'm a bit wary of calling it liquid myself.

#2. Its not glass. "Glass" isn't bulletproof. "Bulletproof glass" is only so named because it fulfills the function of glass despite being made of something different. I'd suggest Wikipedia if you want more details on that.

#3. Its a single mass... and it has a particular vibration frequency dependant on its density and volume. If you play that single note... i.e. its vibration frequency... at a high enough volume then the glass will crack or shatter (though the act of cracking it will break it into smaller pieces, which themselves may need different frequencies).

#4. Same frequency as to break it... but just introduce it from nothing immediately to an absolutely obscene volume (think airplanes taking off or volcanoes erupting at point-blank range). That would probably break it pretty bad. Getting it to disintegrate to microscopic pieces though? Thats probably not possible.

#5. Simple. The glass is 3D. The cracks aren't uniform all the way through... They have a three-dimensional structure that holds it together like a jigsaw-puzzle... albeit in many cases rather weakly (hence why some pieces will fall out).
In other words the cracks going -through- the glass (as opposed to across the glass) won't all be parallel, and hence force applied through the glass will be transmitted in different directions dependant on the angle of the interfaces, quite possibly holding it all in place due to pushing in contrary directions simultaneously.


I hope that explains it well enough... though its difficult to express some of it in words.

Answer 2

1. glass is amorphous silicon dioxide. amorphous meaning lacking in structure. yes the silicon and oxygen atoms have lost the macromolecular tetrahedral structure that gives it high melting point and structural integrity. when you melt sand, the entire structure is destroyed, when allowed to cool, the molten sand solidifies fast enough so that the structure does not rebuild, resulting in a SOLID glass with arrangement of atoms much like a liquid. the term is amorphous solid.

2.glass is made bullet proof or bullet resistant by layering the glass with polycarbonate, a type of hard plastic. the lamination keeps the the glass in one piece despite it being already broken to a million parts. this is useful for car windshields so that in the case of accidents, teh shattered windshield does not become shrapnel.

4. breaking glass with sound is possible. you need to play a sound at a frequency close to or equal to the resonant frequency of the glass. then, the sound must be of a large enough volume to actually do damage. the process is self destruction. ie, the glass vibrates so much that it cracks itself. also, the cracking of glass occurs along fault lines at the molecular level. there is no such thing as a perfect glass, so any cracking is seen as a random event. there is no predicting to how many pieces a pane of glass will shatter to when you hit it. as to the question on totally disintegrating the glass with sound, that might be a possibilty in the future especially for weapons development.

5. as mentioned, glass that breaks without collapsing is held in place by an external structure such as a lamination like polycarbonate plastic or polyurethane.

Answer 3

I know the answer to #1. Glass comes from rock and water. That is the natural process anyway, made just like crystal's, after so many years of water streaming over rocks, glass is made. For the history of glass, here is a link for you. It's nice to know someone is interested in something so highly that isnt sex! LOL