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Harut82
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didn't know where to post it so I put it here
do you guys agree with the following?
do you guys agree with the following?
http://encyclopedia.thefreedictionary.com/glassOne common belief is that glass is a super-cooled liquid of practically infinite viscosity when at room temperature. Supporting evidence for this position is that old windows are often thicker at the bottom than at the top. It is then assumed that the glass was once uniform, but has flowed to its new shape.
One possible source of this belief is that when panes of glass were commonly made by glassblowers, the technique that was used was to spin molten glass so as to create a round, mostly flat and even plate (the Crown glass process, described above). This plate was then cut to fit a window. The pieces were not, however, absolutely flat; the edges of the disk would be thicker because of centripetal forces. When actually installed in a window frame, the glass would be placed thicker side down for the sake of stability. Also, the sparkle is greater and the visual effect stronger when the thicker side is down. There is anecdotal evidence that occasionally such glass has been found thinner side down, as would be caused by carelessness at the time of installation.
Writing in the American Journal of Physics, physicist Edgar D. Zanotto states "...the predicted relaxation time for GeO2 at room temperature is 1032 years. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer" (Am. J. Phys, 66(5):392-5, May 1998). In layperson's terms, he wrote that glass at room temperature is very strongly on the solid side of the spectrum from solids to liquids.
Evidence against glass flow
If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more—but this is not observed.
If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then changes in optical telescope mirrors should be observable (by interferometry) in a matter of days—but this also is not observed. Similarly, it should not be possible to see Newton's rings between decade-old fragments of window glass—but this can in fact be quite easily done.
Likewise, precision optical lenses and mirrors used in microscopes and telescopes should gradually deform and lose focus. This is also not observed.