dean@ruby.berkeley.edu (10/15/86)
My understanding of the difference between a solid and a fluid comes from the engineering principles used in biomechanics. A solid is a material that deforms under load but whose original dimensions are restored when the force is removed (it demonstrates elasticity). A fluid is a material that deforms under load but whose original dimensions are _not_ restored when the force is removed (it demonstrates viscosity). In fluids, but not in solids, the particles within it translate past each other permanently under influence of an external force. An interesting thing about this definition is that it may be time-dependent for real materials: a thick solution of corn starch in water will flow if poured slowly (it's a liquid at that timescale) but shatters if hit with a hammer (in that case it's a solid). There is a continuum of behaviors from a perfectly elastic solid to a perfectly Newtonian fluid. By this definition, glass is a solid at short timescales (bend a glass rod between your hands and it springs back to its original shape) but a liquid at long timescales (large windows flow due to gravity). -Dean (dean@ruby.berkeley.edu) [The opinions expressed herein are mine, but someone else probably believes them, too.]
rpw3@amdcad.UUCP (Rob Warnock) (10/23/86)
In article <1454@jade.BERKELEY.EDU>, dean@ruby.berkeley.edu writes: > An interesting thing about this definition is that it may be time-dependent > for real materials: a thick solution of corn starch in water will flow if > poured slowly (it's a liquid at that timescale) but shatters if hit with a > hammer (in that case it's a solid). There is a continuum of behaviors from > a perfectly elastic solid to a perfectly Newtonian fluid. Conversely, there are materials which are called "thixotropic" (spelling?), which are solids if stressed slowly and liquids if stressed quickly. A good (or should I say, bad) example are certain kinds of mud (or wet ground, as after a long rain) which, when a small earthquake comes, suddenly liquify and bury people. Another example is a kind of heavy stucco paint, which sprays quite tamely through a paint sprayer (liquid), but which as soon as it lands becomes "solid", allowing one to spray extremely thick, built-up layers on a vertical wall. Rob Warnock Consultant {amdcad,sun,fortune}!redwood!rpw3
jmc@riccb.UUCP (Jeff McQuinn ) (10/29/86)
> > Conversely, there are materials which are called "thixotropic" (spelling?), > which are solids if stressed slowly and liquids if stressed quickly. A good > (or should I say, bad) example are certain kinds of mud (or wet ground, as > after a long rain) which, when a small earthquake comes, suddenly liquify > and bury people. Another example is a kind of heavy stucco paint, which > sprays quite tamely through a paint sprayer (liquid), but which as soon as > it lands becomes "solid", allowing one to spray extremely thick, built-up > layers on a vertical wall. > > Rob Warnock > Consultant > {amdcad,sun,fortune}!redwood!rpw3 Finely divided coal exhibits this characteristic also. You can swirl it around in a bucket and it behaves for all the world like a liquid. Incidently; Van Nostrum flatly states that glass is a solid. It sometimes shows properties like those of a super-cooled liquid. Jeff McQuinn just VAXing around
magik@chinet.UUCP (Ben Liberman) (10/31/86)
In article <754@riccb.UUCP> jmc@riccb.UUCP (Jeff McQuinn ) writes: >> >> Conversely, there are materials which are called "thixotropic" (spelling?), >> which are solids if stressed slowly and liquids if stressed quickly. A good > >Incidently; Van Nostrum flatly states that glass is a solid. It sometimes >shows properties like those of a super-cooled liquid. > > Jeff McQuinn just VAXing around This is a second hand story - take it as you will! An old trick, used by experienced glaziers on their apprentices was based on the property of glass to micro-fissure when scrached and then "heal" in short order. The glazier, by way of example, would scribe a complex line on a piece of glass and snap it cleanly in two. He would then hand it to the aprentice to scribe and then take it back to examine it while talking at length of the delicate ART of glass cutting. When handed back to the apprentice for snaping, the piece of glass would break anywhere but where it was supposed to. I have also heard that the large store front windows on the downtown Chicago stores (Marshall Fields, etc.) would be removed and rotated every few decades to prevent breakage because the glass would get thicker at the bottom and thinner at the top. From the rumor mill: ---------------------- Ben Liberman ihnp4!chinet!magik or ihnp4!homebru!magik
alanj@orca.TEK.COM (Alan Jeddeloh) (11/03/86)
In article <703@chinet.UUCP> magik@chinet.UUCP (Ben Liberman) writes: >I have also heard that the large store front windows on the downtown Chicago >stores (Marshall Fields, etc.) would be removed and rotated every few decades >to prevent breakage because the glass would get thicker at the bottom and >thinner at the top. The house I grew up in is now ~75 years old. The large plate glass windows in the living and dining rooms have developed very slight, but noticable, sags. -- -Alan Jeddeloh Tektronix GTD tektronix!orca!alanj
pamp@bcsaic.UUCP (wagener) (11/05/86)
In article <754@riccb.UUCP> jmc@riccb.UUCP (Jeff McQuinn ) writes: >> > >Incidently; Van Nostrum flatly states that glass is a solid. It sometimes >shows properties like those of a super-cooled liquid. > > Jeff McQuinn just VAXing around Glass - "A state of matter intermediate between the close-packed, highly- ordered array of a crystal, and the poorly packed, disordered array of a gas. Most glasses are supercooled liquids, i.e., metastable, but there is no break in the change of properties between metastable and stable states. The distinction between glass and liquid is solely on the basis of viscosity, and is not necessarily related, except indirectly, to the difference between metastable and stable states." (Dictionary of Geologic terms,American Geological Institute,1976,p.188.) "...a mass that cools to a rigid condition without crystalization...." (Websters 9th New Collegiate Dictionary,1984,p.520.) Everything I've consulted (the above are only examples that are available right now) point out that glass is a very highly viscous, supercooled liquid, not what is classically called a solid. Does anyone have a real good definition of a solid? Most of the definitions I've run across for solids define them as crystalline substances, or at least have the properties of an orderly arrangment of basic units. As far as I know glass has no ordering of its elements, hence its classification as an amorphous substance. Anyone have any good references on hand? Just curious, Pam Pincha-Wagener
bs@linus.UUCP (Robert D. Silverman) (11/24/86)
In article <769@bcsaic.UUCP>, pamp@bcsaic.UUCP (wagener) writes: > In article <754@riccb.UUCP> jmc@riccb.UUCP (Jeff McQuinn ) writes: > >> > > > >Incidently; Van Nostrum flatly states that glass is a solid. It sometimes > >shows properties like those of a super-cooled liquid. > > > Everything I've consulted (the above are only examples that are > available right now) point out that glass is a very highly viscous, > supercooled liquid, not what is classically called a solid. > > Pam Pincha-Wagener etc. I was the first to suggest, in response to the query about H-less liquids that glass was in fact a super-cooled liquid. It does flow at room temperature. I received numerous flames, most suggesting that I was not playing with a full deck. I think the many followup discussions have showed that glass can be considered to be a liquid (depending on definition). Please people, before you start flaming fellow posters for something that might be a matter of definition, check it out first. I received a least 10 private letters suggesting that my intelligence was somewhat lacking for posting such an absurdity. Bob Silverman