Oh rubbish. That may be the way that science works, but it isn’t the way language works. It’s important to realize that words can have both a popular and a technical meaning, and both are equally valid within their own realms. Glass may very well be a liquid to a scientist, and it’s fine to refer to it as such in technical applications. But it is certainly a solid the way that most people understand the word. That’s not ignorance, it’s plain English. It’s fine if scientists wish to take common words and redefine them for technical applications, but to allege that it is “ignorant” to continue to use the word according to its original meaning is pure arrogance.
(And my take on this is as a professional scientist.)
“Ignorance” was a tad on the harsh side, I’ll admit. I took issue with an existential answer to a reasonably cut-and dried question in the assumption that the OP was asking for a call from a scientific viewpoint. Otherwise, wouldn’t it be better suited to IMHO (“Hey! Who here thinks glass is a solid?”) or perhaps GD (“where do we draw the line between true solids, amorphous solids, and liquids, and what do we mean by the word ‘solid,’ anyway?”)?.
I thought GQ was intended for “factual” questions and answers. Shoot bullets through me.
Why is it that the “liquid” designation seems to be only applied to glass? A little superficial Googling and Wikipedia reading tells me that plastics are amorphous solids as well. Should they be considered to be liquid as well? Certain igneous rocks are not crystalline - are they liquid? What about liquid crystal; they have crystalline structure, but they flow. Are they solid?
No you are correct–I was seeking a scientific viewpoint. I can see for myself that glass is a solid as a lay person. But her comment was that her science teacher stated this-so I was going on the base assumption that technically there was something beyond what the common assumption would be.
thank you all for your explanations–I should have done a search :smack:
but you live and learn
thanks again!
The trouble is that the microstructural and (continuum) mechanical definitions have nothing in common. They don’t even address the same question. This is at the root of the “glass is a liquid” business. Glass shares certain microstructural characteristics with other materials that everyone recognizes as liquid. For people who are interested in microstructure, there is value in classifying glass as a liquid (I guess; I’m not a materials scientist.) But the mechanical definition is a lot closer to the layperson’s intuition than the microstructural definition. That’s why people looked at the thickness of old windows and such things - they learned that microstructurally, glass is amorphous like liquids, therefore, they reason, it must flow like a liquid. Only it doesn’t flow. There is a correlation between amorphousness and flow, but there are exceptions. Glass is amorphous but doesn’t flow. Liquid crystals are crystalline, but they do flow.
All of those can melt under the right circumstances. Wood and sulphur would have to be in an absence of oxygen. Dry ice (aka carbon dioxide) would have to be under pressures greater than 1 atmosphere. I don’t think there’s any crystalline solid that doesn’t melt under the right circumstances, whereas amorphous solids never will.
[QUOTE=Hyperelastic
A better way to look at it is from a mechanical point of view. The most common definition of a fluid (which generally comprises what physicists refer to as liquids and gases) is a material whose shape can be changed without affecting the way it responds to subsequent shape changes, i.e., it has no “mechanical memory”. .[/QUOTE]
what about viscoelastic or thixotropic fluids? They certainly have a “memory” !. Sorry, nature is never so cut and dry
You bring up a valid point - this is why I admitted to a loss of clarity when I gave the definitions of fluid and solid.
To go into more detail, elastic fluids do have “memory”, but they do not recognize one configuration as different from another. So it limits the way in which the “memory” can affect the response. The past only affects them in so far as it differs from the present configuration, but that is always changing. This is a subtle issue that I didn’t want to go into. It’s easier, but inaccurate, to just say that fluids don’t have “memory”.
Also, note that we’re talking about mathematically idealized materials here, not real materials. So the problem isn’t with nature, it’s with our inability to unambiguously describe phenomena that are inherently ambiguous.
Hyperelastic*
Also, note that we’re talking about mathematically idealized materials here, not real materials. So** the problem isn’t with nature, it’s with our inability to unambiguously describe phenomena that are inherently ambiguous.***
And our inability to explain all phenomena of the natural world is that we are not taking into account the tenets of Intellgent Design.
(The above is stated as a 100% tongue-in-cheek posting.)
Now you’re getting my point! A lot of things we perceive to be solid have slightly different characteristics than those that we attribute to “pure solids.” Hence my discussion of candies and rocks.
Again, to my understanding, molecules in “solid” crystalline structures have more… reason… to stay put. (Intermolecular bonds) Molecules in amorphous structures lack the bonds between molecules. Said molecules may move so slowly that we consider the overall sample to be “solid,” but molecular movement happens.
Granted, it happens in metals as well. matt mentioned lead as an example, but all metals (which are usually crystalline) can display creep, from the kind of intermolecular bond that’s present.
This is problem related to our definitions. We think in terms of pure characteristics (solids don’t change shape, ever; liquids change their shape easily). I actually like terms like “semi-solid” or “semi-liquid” to describe substances with unusual combinations of characteristics.
Liquid (fluid, inviscid, with minimal viscosity): water, alcohol, oil
Gas (fluid, compressible): air…
Although each term may share characteristics with other terms, no two terms share all charateristics. Of course, most substances here are “pure.” When you want to define things like ice cream or fudge, you would need definitions like “crystalline particles suspended in an amorphous gel or matrix.” Me, I’d rather eat them and call 'em “snacks.”
Incidentally, the term “true solid” seems to be something bizzwire made up. A non-scientific Google search finds only 11,600 hits for the phrase, the first page of which seems to be mostly companies selling refrigerators. “Crystalline solid”, on the other hand, get 88,200 hits while “amorphous solid” gets 31,100 hits. So my take on this is that scientists classify “solids” into two types, “crystalline” and “amorphous”. Glass is an example of the latter type, which makes it … still a solid.
