Is glass a liquid, or a solid?

Cecil’s column

An article on MSNBC today:

I’m not sure I’d put too much stock in that article, since they repeat the tired myth about medieval window glass showing sings of sagging.

I noticed that.

I think it really comes down to definitions. Cecil says some mathemetician did the calculations to determine that glass would thicken 5% at the base over 10 million years. First of all, lets keep in mind that computer modeling isn’t any where near that good. Whatever calculation she did used many assumptions and fudge factors. I’m not saying it wasn’t a reasonable estimate, but I wouldn’t reference it in a paper. Discover Magazine isn’t exactly the same caliber as Nature. I would take that estimate with a whole shaker of salt.

Strangely, I would call glass a glass. I would define a glass as an amorphous solid. It is different from a crystalline solid and it has some characteristics of a liquid. Still, I think calling glass a liquid reaks of fact dropping to prove your smart. For almost all real world applications, glass behaves like a solid. Plus, calling it a liquid confirms peoples mistaken idea that medeivel windows are sagging.

We address the issue previously.

We address it before that

And numerous times before that, too many to make links for.

ETA: Ok, I’ll add one more time we discussed it.

Glass is a liquid in the same sense that it’s an electrical conductor. Yes, it has a finite viscosity, but it also has a finite resistivity. It’s just that both of them, while finite, are still really, really high. So if you’re going to divide substances into “liquid” and “solid” based on their viscosity, or into “conductors” and “insulators” based on their resistivity, then it makes sense to call glass a solid and an insulator.

It depends on how you define liquid from solid.
Is anything that can be made liquid at a temperature before it combusts considered a liquid?
Is it considered a liquid because it is a liquid at most temperatures we’re likely to deal with it at?
Is it a liquid because more of it’s liquid than solid on this planet right now? Where exactly is the definition?
Perhaps it’s a solid because of the type of crystalline structure after it forms?

That’s like saying that metal is a liquid because it’s liquid at certain temperatures. “Really, really high ones?” “Sometimes … what about mercury?”

What about water - there’s plenty of it in a solid state right now … and what about “rocks” ?
Solid or liquid? I wonder what percentage of the earth is made of solid “rock”-like material, and what is liquid (right now)?

The liquid and solid determinations are made at STP - Standard Temperature and Pressure, which would be 25 °C and 760 mm Hg (298 K, 101.5 kPa), or in some instances at a specifically defined condition. So glass is a solid, albeit an amorphous one, at standard conditions.

Then what is pitch?

That’s kind of a screwball experiment.

How is is screwball?

A “screwball” is a type of pitch.

Hmmm. I’ll accept the whoosh, but I think it’s a stretch.

My chem101 teacher defined states of matter as follows:
A solid is a substance with a definite volume and a definite shape
A liquid is a substance with a definite volume and no definite shape
A gas is a substance with no definite volume and no definite shape

While this may be oversimplifying when you get into higher levels of chemistry and physics, it’s certainly clear enough for an article written for laypeople. Laypeople can recognize that heated, molten glass is certainly a liquid. What they’re addressing is glass at room temperature. So once again, we’re back to the question - does glass at room temperature change shape? Most people say no, or not at rates meaningful within a human lifespan, and so therefore we might as well call it a solid.

Yes, it is liquid at that temperature. Any element which maintains its molecular stability can be made gas, solid or liquid by changing the temperature and/or pressure. (In theory, anyway, I’m not sure if it’s practical to do so for all substances.)

Nothing is always a liquid. You need to be more specific about the substance, temperature and pressure.

Are we talking about water? Water, unlike most things, is found on our planet, without human fiddling, in all three forms. Water isn’t a liquid, water is *sometimes *a liquid. Sometimes it’s a gas and sometimes a solid. In my kitchen, it’s found in all three forms at once.

See above. It has nothing to do with quantity, only the properties of the specific sample in question. “Water is liquid” is a meaningless and false statement. “This sample of water is liquid.” or “Water is liquid between 1 and 99 degrees Centigrade at 1 atm” are meaningful statements.

Metals can be liquid, although each has its own temperature at which it becomes liquid. “Metals” is not a substance, it’s a group of substances which have certain characteristics in common (they are shiny, they conduct electricity, they are generally (but not always) solid at STP and they generally (but not always) have a relatively high melting point when compared to non-metals and metaloids.

“Water” doesn’t tell us enough - we need the temperature and pressure to determine the state. “Rocks” is, again, not a substance. You must be more specific about the substance and the temperature and pressure.

Only if there’s a man on base.

A little over one drop per decade. Wow!

Glass is a liquid?
What, are you going to tell me a tomato is a fruit next?

Yep! But that’s okay, 'cause pineapple isn’t. (Nor does it grow on trees.)

I don’t get it. Nobody ever asks “Is a carrot a vegetable, or a root?”, or “Is lettuce a vegetable, or a leaf?”. But both of those questions have exactly the same structure as “Is a tomato a vegetable, or a fruit?”.

For that matter, nobody ever seems to ask the vegetable/fruit question about peppers, cucumbers, eggplants, green beans, or any of the other fruit vegetables, either. It’s only ever tomatoes.

I’d say that for most, if not all, practical considerations the question of whether or not glass is a liquid is pretty moot.

Except, of course, as a stoner conversation topic:
Stoner A: “Dude, did you know that glass is, like, a liquid?”
Stoner B: “No way, man!”
pause as the topic is briefly forgotten
Stoner A: pours some water into a glass
Stoner B: “Dude…”
Stoner A: “What?”
Stoner B: “You just, like, poured a liquid into another liquid!”
Stoner A: “…Whoa. Far out, man.”
Stoner A: proceeds to take a sip
Stoner B: “I mean, how can you even do that?”
Stoner A: “Do what?”
Stoner B: “Drink one liquid, but not the other!”
astonished silence
Stoner A: “That must be why it’s called ‘drinking a glass of water’!”
Stoner B: “But now… is it half full, or half empty?”
Stoner A: “Oh, just shut up.”

This is totally not based on a conversation I once had with a friend. Don’t take drugs, kids!