My High School chemistry teacher told us 20+ years ago that glass was a liquid and cited the flowing windowpane story as conclusive evidence. I was skeptical then, and after reading all of these posts and links, I know he was as full of crap as I always thought he was.
Anyway, it seems settled that Cecil admitted he was incorrect, or at least did not fully research the topic before answering. In my wanderings, I found this site: http://www.ualberta.ca/~bderksen/florin.html#intro
which seems to have collected many of the critical references.
I’ve been trying to find information on an in-between state of matter which I think is called a rheoid (something like that). It is described as having properties of a liquid and a solid (such as large masses of glacial ice). Anybody else heard of this?
The term “plastic” usually refers to how a material behaves as it is stretched. Plastic deformation means that if you apply a stretching force, the material will stretch more or less linearly with the force (Hooke’s law), and then suddenly start stretching in a screwy, non-linear manner. The alternative, as most materials behave, is that after the linear regime over, and the maximum tensile strength is exceeded, the material will break rather than stretch any more.
So, for example, a piece of bubble gum is plastic, since you can pull and pull and it keeps stretching, but a piece of glass is not plastic, since it will just snap when you pull on it too hard.
I thought plastic refered to being moldable as in clay. Even metal goes through that state as it cools. Ah yes I remember welding class.
In chemistry class we used to bend glass tubes by holding them over the bunsen burner till they turned plastic Sometimes we would stretch them to a thread.
Not quite. In this sense, plastic deformation refers to deformation that is not recoverable. Elastic deformation is deformation that is recoverable. What does that mean? If you pull something in that linear region of the stress/strain curve, then release the pull, it will return to it’s original shape. (Stress is internal load, strain is deformation.) Plastic deformation is the unlinear odd stuff at the end, where it deforms and does not return to original shape.
Either plastic or elastic behavior can apply up to the tensile strength, depending on the material. That gets into ductility, which is the amount of “give” in the material, and whether it is very brittle (glass) or very ductile (silly putty).
Metals typically have a fairly large elastic (linear) region, then hit the yield strength where they start deforming plastically, and finally an ultimate (tensile) strength where they fail (break). They can have different traits on ductility (steel vs. copper). Plastics are materials that have very small or no elastic deformation region, but have deformation that is not recoverable. The strength of the material is a property of the material independent of whether it is plastic or elastic.
Thanks, I was also going to include that in my post, but forgot. I realized it later, but by the time I checked back you had already made this (excellent) post.
Some years ago, in my wanderings through various and eclectic scientific journals and cool articles, I found a piece where this had been demonstrated. Apparently, someone had obtained a chunk of intact window glass from colonial times out of a building which had survived and measured the thickness of the piece from the top to the bottom.
Back then, plate, or window glass was poured out onto a slab, allowed to ‘settle’ and then placed through the gradual cooling process without being pressed – which gave it the not all that clear appearance. There was a measurable difference between the top of the glass and the bottom – which was THICKER. Not by much – we’re talking fractions of fractions of an inch here, but enough all across the bottom length to compensate for any naturally occurring irregularities of the glass and to demonstrate that the glass, over a couple of hundred years, had ‘flown’ downward.
Rainbow, please read the other threads that have been linked to here. For the last time, glass is not a liquid. It is an amorphous solid. This cannot be made any clearer.
Excuse me for entering late, but I couldn’t resist.
So according to one guys calculations glass will flow in 10 million years. It’s possible, but how reliable are those calculations over 10 million years.
Even if that is the case, it is only true for one type of glass cooled at one particular rate. As a glass is cooled, it develops crystalline and non-crystalline domains. The faster the glass is cooled, the less time it will have to develop crystalline domains. This will effect the rate at which any glass will flow.
Someone said that the solid at the bottom of the honey container was precipitated sugar. That is wrong. It is crystallized sugar. Since honey is in an of itself that sugar, there is no solution for it to precipitate from. Actually, honey makes a perfect demonstration for difference in cooling rates of glasses. If you stick honey in the refrigerator it will not crystallize, but will form a glass.
Glass is not a plastic, but plastic can be a glass. That is what happened to the O-rings on the space shuttle Challenger when the temperature got below the glass transition state.
Have any Dopers seen window glass installed in houses or other structures in the New World, or anywhere else, in the 17th Century? (item: Harvard was founded in 1636.) According to Isaac Asimov in Building Blocks of the Universe, a compound in window glass changes over time, so that the window takes on what Asimov (who lived in New England for many years) called a “delicate violet tinge”; he said such windows are prized these days as antiques. Having never been farther east than Beech Grove, Indiana (and not having even been there since 1965), I cannot personally vouch for this.
From The Teachers an Pupils Cyclopedia Gray Publishing Co 1911
The melted material …is dipped by workmen with an iron tube, called a blowpipe…
Sheet glass is made by taking the melted material from the pot ,when it is blown and
whirled until it assumes a cylindrical form. The ends are then cut off ,the cylinder is then
cut longitudinally, and the sheet is heated, pressed and rubbed until it is flattened out.
Plate glass is made by pouring the melted material upon a table, which has a marginal
edge equal to the thickness of the glass. It is then flattened out by a roller passed over the
table, resting on the edges, and thus secures equal thickness throughout.
I remember sitting in grade school looking out the window wondering how that elongated
bubble got in that glass.
This book mentions neither Supercooled liquid or amourphous solid. Niether does a 1951
encyclopedia I’ve got.
have a nice day
“And thats all I’ve got to say about that” Forrest Gump
Yes, my freshman physics teacher told us that windows in old buildings are thicker at the bottom because the glass flows. And I believed it.
Then three or four years ago, I came across the alt.folklore.urban threads on glss flw, did some reading, and came across rigorous-seeming calculations that showed that if glass were to flow perceptibly, it would take so long that our 15-billion-year-old universe would seem like a blink in time.
Now I learn that there is an article in Discover which says that a window pane could get 5% thicker in 10 million years. Granted, this is a long time compared to human scales, but if true, we should be able to detect flow of smaller distances in our lifetimes.
I’m not a materials scientist, but here’s my thoughts - I’d appreciate someone fixing up my estimates. First, I’d guess that a standard-size old window pane is maybe 30cm square. For it to get 5% thicker, I’d guess that some molecules have moved 2 or 3 cm. This gives a rate of 2 or 3 nanometers per year.
When I was younger, I recall reading an article about polishing a large telescope lens to an accuracy of around a millionth of an inch, or about 40 nm. So you should be able to detect a change in 20 years or so. It’s been longer ago than that since I read the article.
So my back-of-the-bar-napkin calculations lead me to believe that if Discover’s calculations were correct, flow would have been observed. I don’t believe it, but I haven’t read the article either.
Remember that hers was a back of the envelope estimate (ok, not “remember” 'cus you didn’t read the article). She specifically said something along the lines of it being undectable in human terms.
First problem is that you’re thinking of a window getting wider not thicker. The thickness of a pane of window glass is probably less than a centimeter. So that throws off all your calculations by quite a bit right there.
The problem there is that it’s not a window and gravity is working on it differently (not all pulling down) and that because it’s so finely polished, other problems can occur that would block any notice if the glass did flow (which I’m still not convinced it does even as little as she claims).
have a nice day