I remember learning it was and as a kid it kinda blew my mind but I was intrigued by the thought. the main reasoning was that old glass panes such as the one in my school were thicker toward the bottom over time. Which meant the glass was flowing like a liquid albeit slowly. Now I see that its not considered a liquid? Not sure why I care. I suppose it comes down to a scientists semantics and which side favors his work.
From my understanding is that it is because glass, in the liquid form, is not its true state. Think of water, it is a liquid, yet you can freeze it. I could be wrong, just winging it.
every substance can be a solid, liquid AND a gas. just depends on the environment. so really its inaccurate to say H2O is a liquid. there is no "true state".
They classify substances generally as to its state at generally accepted atmospheric pressure and temperature. There's a scientific standard out there and whatever your substance is at that pressure and temperature is what dictates whether it is a solid liquid etc. Now of course, everything can be everything as tirk put it but there's a standard state for every substance. As far as glass goes, to me, it's a solid. However, I've never seen glass that was thicker at the bottom because it was melting. From what I understand, if a substance has any viscosity at all, it is a liquid. I don't think glass qualifies at the standard pressure and temp.
if you really want to know. put the substance in a closed paint can, heat to 100F, remove lid, invert and measure flow. if it flows more than 2 inches in 3 min it is a liquid. per ASTM 4359-90. i looked it up in the library at work, no free online source found. it doesnt say how to characterize the substance if it falls out of the can and shatters.
