While I know the chemists will define glass as a liquid since it lacks a crystalline structure, i.e., a latticework at the atomic level. Furthermore, my chemistry teacher (from yesteryear) would claim windows will run out of their sills in maybe a 100 years. She claims they found windows in old churches that are thicker at the bottom than the top which supports this argument - that glass is a liquid of high viscosity.
What’s the whole story on this? Can we witness “running windows” in our lifetime? Where can I find real-world examples in real-time…all around us? (I don’t think I can wait 100 yrs nor take the kids to some old European church!)
No, the whole window glass flowing downwards is a myth. Glass panes when made back in the day were imperfect pours and ended up being uneven thickness. Workers purposely installed them with the thickest side on the bottom for a uniform look.
I could’ve sworn there was a SD column on this but I can’t find it. Anyway, the section on Wikipedia.
Summary: She was operating under an urban legend. Old glass windows are thicker on the bottom solely because of how they were made. Cooling glass spun like a centrifuge and cut to shape. The thicker part was on the bottom because it’s more structurally sound. See also the info on “amorphous solid.”
100 years is an extremely “optimistic” number for other times I’ve heard this UL.
Nope! Your referenced thread includes a link to a Cecil response where he concludes it is a liquid, and it IS flowing, although very, very, very, very slow:
(NOTE: Read in its entirety) …did I say very, very, very slow?
No, he really DID NOT backtrack. At the very, very end, he concludes IT IS FLOWING! Therefore, it IS a liquid. See ya in a million years when my laptop screen puddles all over its keyboard.
Wow, that’s a really bad article. I presume Cecil never looked through a quarz crystal?
Anyway, regarding the original question in the article, why one can see through glass, Pasta does a great job of clearing up the issue in this post, by rebutting the other common misconception, that the light ‘bounces from atom to atom’.
A recent science program on UK television discussed the issue (Dara O’Briain’s Science Club). It dismissed the glass flow issue but mentioned in passing the question of whether Pitch was a liquid and referenced the oldest known continuing experiment to test this empirically (about 70 years) rather than rationally.
Saying that glass is a liquid is like saying that glass is a conductor. Yes, it has a finite viscosity, just like it has a finite resistivity, but they’re both really, really high, such that it’s almost always fine to approximate them as infinite.
The earth’s crust bends and settles, so, it too is a liquid. Large heavy blocks of so-called ‘solid’ metal will deform over time, so, they’re also really a liquid. The real question is “Is solidity an illusion?”
Neither of these are strictly speaking, true. The technical definition of a liquid is a continuum which has no regular structure, a resistance to shear based slowly on the differential velocity, and is in essentially one state with mechanical properties which are isentropic. Most solids, and especially metallic solids and intermetallic compounds, have both a local and global structure (the local metallic lattice and the larger grain structure), a resistance to shear based upon deflection from the equilibrium state, and are not typically isentropic (although many metals are often treated so for engineering purposes). Deformation of solids is caused by adding energy to the lattice in a manner analogous to compressing a spring, or altering the large scale structure. (Some heat treatment, tempering, diffusion, and other processes can also alter the small scale structure by changing the configuration of the lattice.) Liquids, having no structure, will ‘deform’ (flow) permanently in response to any non-equilibrium loading.
Glass is best characterized as an amorphous solid; that is, it has no large scale structure, and only a very irregular short range structure. It is true that glass and glass-like substances will start flowing under sufficient heat or pressure (which are far greater than anything experienced in typical terrestrial conditions), and the lack of well-defined structure means that unlike solids, there is no well defined line at at which a phase transition occurs; hence why you will see engineers arguing over the “glass transition temperature” of a particular substance with a wide range of temperatures depending on the particular set of mechanical characteristics they may be concerned about and/or the conditions and methods by which which it may be experimentally determined.
“Solidity” at the macroscopic level is generally well-defined insofar as solid objects will fracture or be permanently deformed when stressed excessively, while liquids will flow and reform to match the shape of any container they are poured into. At the molecular and atomic level, solidity is much more vague, and in fact the boundary between a control volume and the area adjacent to it isn’t even well defined, as individual atoms and molecules may separate and recombine continuously.
