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Is glass a solid or merely an extremely slow-moving liquid?

news.emory.edu — Physicist opens new window on glass puzzle.

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  • petsheep, on 10/10/2007, -12/+5great article
    • SillyRabbits, on 10/10/2007, -1/+34Not really. It's pointless to argue solid/liquid. They aren't scientifically precise and it's just semantics. When scientists talk about the distinction they refer to whether the material has a long or short range order, or the viscosity, etc. Arguing solid/liquid is like trying to explain the flavor of coffee just using the terms bitter and sweet. This looks like another example of a researcher making the material easier for the author to understand and the author missed what was really neat about the research (which in this case seems to be whether glasses have a sort of quasi-long or medium range order - but I can't tell from what the author wrote).
      • physphd, on 10/10/2007, -2/+4"In thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another. The distinguishing characteristic of a phase transition is an abrupt sudden change in one or more physical properties, in particular the heat capacity, with a small change in a thermodynamic variable such as the temperature.

        In the English vernacular, the term is most commonly used to describe transitions between solid, liquid and gaseous states of matter, in rare cases including plasma."

        http://en.wikipedia.org/wiki/Phase_transition
        • GMorgan, on 10/10/2007, -0/+1Phase transitions are mostly shown by apparent loss/gain of heat. There is a latent heat value associated with each state transfer. If you carefully measure the temperature changes you will see the temperature gauge sit still as you pump heat into it, this is indicative of a state change. Of course this is overly simple because there are things like microstates, there are something like 8 different types of ice.
        • 10001, on 10/10/2007, -1/+5^^ 8 types of ice:

          dry ice, ice cubes, ice cream, black ice, shaved ice, ice berg, ice tea, ice age
      • 10001, on 10/10/2007, -5/+1wikipedia != truth

        wikipedia is a neologism... those are apparently not welcome in wikipedia

      • NerdyNinja, on 10/10/2007, -0/+3Sure it's scientifically precise. There's clear jumps in the amount of energy it takes to move from one state to another. Now the REAL question they should be asking is what the hell state yogurt is in!
      • theOster, on 10/10/2007, -0/+1i thougth the main distinction in this topic was "liquid" vs. "fluid". i always thought glass was a fluid (though solid).
    • defectDS, on 10/10/2007, -0/+4I brought up this same question in my chemistry class a few years ago and I was scoffed at by the teacher and the whole class. Was it really that stupid of a question?
      • yosempai, on 10/10/2007, -0/+5My highschool science teacher taught me about this. Freshman year.
        • Travisty2012, on 10/10/2007, -0/+2Same here. I was taught early on that glass was an "amorphous solid."
    • kibiz0r, on 10/10/2007, -1/+12Does it bother anyone else when people make comments that just say "great article"? I thought that's what the "digg it" button was for...
      • alecks, on 10/10/2007, -0/+9I agree with what you're saying. You get my proverbial "thumbs up"!
    • Mimorox, on 10/10/2007, -1/+1http://en.wikipedia.org/wiki/Glass#Glass_as_a_liquid
    • bdit1200, on 10/10/2007, -1/+3pic, or it didn't happen...
  • theholotrope, on 10/10/2007, -13/+51"Physicist opens new window on glass puzzle."

    Are you taking English 101?
    • CasinoJack, on 10/10/2007, -2/+47Dugg for the awful pun.
      • zip000, on 10/10/2007, -11/+4Maybe I missed it, but I don't see a pun there.
        • AnarchyReigns, on 10/10/2007, -1/+4Windows are made of glass...
        • rabidg00se, on 10/10/2007, -0/+13zip, you're a real pane.
        • zip000, on 10/10/2007, -8/+2Windows are made of glass, but that doesn't make that a pun.

          Some pun examples: (most from wikipedia for convenience)

          Q: What instrument do fish like to play? A: A bass guitar
          One of these new shoes isn't right.

          See, its about substitution of a homonym or even just a similar sounding word. Windows being made of glass doesn't a pun make.

          (I know I'm being pedantic)
        • zip000, on 10/10/2007, -0/+1Thanks rabidg00se, that is a terrific pun :-)
    • mrfish, on 10/10/2007, -0/+1Description says it all.... *sigh*
  • Terr01, on 10/10/2007, -11/+5Side note: One of the arguments for "glass as liquid" has to do with stained-glass windows, and their glass pieces being thicker on the bottom than on the top. Of course, this could be for purely structural or intial manufacturing reasons rather than a symptom of age.
    • geekchic, on 10/10/2007, -4/+5You might want to read up on the "pitch drop experiment" then, which shows that "solids" can behave like slow moving liquids. There is a version of the experiment for glass being carried out, but I can't recall which university is doing it.
      • rajun50, on 10/10/2007, -0/+1University of Queensland
      • asteron, on 10/10/2007, -1/+4Pitch is a liquid. The flask of glass that the pitch is in for the pitch drop experiment is a solid. Why would they put a liquid in another liquid?

        I don't believe that there is any equivalent experiment for glass being currently being carried out that has observed any flow at room temperature.
      • Terr01, on 10/10/2007, -0/+2Demonstrating that there are extremely-viscious liquids is not per se an argument that a given material is liquid and not solid.
    • SillyRabbits, on 10/10/2007, -3/+10Old windows have never been an "argument" for glass as liquid. It is well known that the thickness difference was due to manufacturing techniques and there are many examples where the windows are installed with the thick part at the top. Besides, it is in no way, shape, or form a scientific test. It can also be easily calculated that, based on the viscosity of the window glass, that is will literally take several million years to see the degree of flow required for the observed thickness variation.
      • alexforcefive, on 10/10/2007, -0/+4"Old windows have never been an "argument" for glass as liquid"

        Tell that to my old chemistry teacher. British education system FTL :(
      • deadmann, on 10/10/2007, -0/+1Well, I learned something.
      • Terr01, on 10/10/2007, -0/+1I want to clarify: I do not agree with the "old windows theory". I was just bringing it up.
    • Sparhawk2k, on 10/10/2007, -0/+1We have a stained glass window that was propped up wrong (only a couple pieces added in the middle to raise it up to fit in the window) but it has since bended down around those pieces where it wasn't directly supported. It's rather funny looking.
    • masgrada, on 10/10/2007, -3/+2If you get old barn and house window pane glass you'll notice that on the bottom is always thicker than the top.
      • SkippyDoorknob, on 10/10/2007, -1/+6Because it was installed with the thicker part at the bottom in order to be more stable. It used to be very hard to make glass at a consistant thickness.
    • Bdog2g2, on 10/10/2007, -2/+1There have been reports of glass vases and cups uncovered in archaeological that where "squished" because of the material, usually part of a structure, pressed down on them. The pressure from the above material hastened the "flow" of the glass. Any material with a regular crystalline structure (short of modern materials) would have simply sheared or broken away.
    • bbardlbradd, on 10/10/2007, -1/+3I have a 47 Oldsmobile 88 Dynamic Cruiser... with original glass, and the windows on it are thicker at the bottom and there are bubbles in the glass near the bottom... why is this? Also, there's a place were a screw was missing in the rail that holds the passenger side window up, and now, in the glass there's an outward jutting lump of glass that nearly plugs that hole... any Ideas? (This isn't the same on the driver side window where the screw is in place.)
      • Ibox, on 10/10/2007, -2/+2You live in a very hot climate?
      • asteron, on 10/10/2007, -2/+3They didn't have as high quality glass in 1947. That glass is the same as when it was installed.
        • bbardlbradd, on 10/10/2007, -0/+1How does that explain the bulge of glass in place of the missing screw?
      • bbardlbradd, on 10/10/2007, -0/+1Well, yes and no. I live in Bakersfield Ca. but the car spent most of it's life in LA and the Fresno area. So... 112+ in summer, around 40 in winter... on average. Is that hot?
      • bbardlbradd, on 10/10/2007, -0/+1Oh SNAPS... I have undeniable proof that it's NOT the quality of the glass... I took it on a 160 mile trip last year, the points in the distributer went out, It died on the freeway, I left it there, got a ride to a pay phone, called someone, came back... and the passenger window was cracked... I don't know how it happened b/c I was parked next to a big empty field at night with the passenger window facing towards the field... so it couldn't have been a rock...

        But, I was cleaning it the other day, not thinking about the whole glass thing, I looked over at the crack in the glass (a vertical fault that runs from the bottom center of the window up, then about half way, splits off into two cracks, like a Y). I found a bunch of bubbles running along crack in the glass... all the way up. There isn't one spot along the entire fault that isn't followed by a series of bubbles, I'll post a link of a picture someday... but it looks like this post is dead.
  • Philluminati, on 10/10/2007, -41/+5This is a stupid article. It's always been common knowledge that glass is a liquid. That's why the windows are thicker at the bottom than at the top in old churches!
    • SillyRabbits, on 10/10/2007, -6/+11Ummm, NO! True, glass has a viscosity, but that's not why old windows are thicker at the bottom. I wish people would stop repeating this.
      • jackhole, on 10/10/2007, -2/+21To clarify: the old glass used in those churches was formed by blowing molten glass into an orb, then spinning the glass into a disc. The disc was then cut into panes. This centripetal process accounts for the ostensibly liquid "ripples" seen in old glass panes, along with the uneven glass thickness. After cutting the panes, the glazers obviously and sensibly arranged the panes so that the larger end would be pointing down. Glass does not "flow" downwards, it was made that way.
      • Apokalyps2547, on 10/10/2007, -2/+7More on what jackhole said:
        Some glazers DIDN'T put the thicker side down, and in some churches, the thicker side is on TOP because of it!
      • unin5pired, on 10/10/2007, -0/+0Actually, by definition the viscosity of a glass is undefined. Glasses do not have a viscosity in the same sense as a traditional fluid.
    • Philluminati, on 10/10/2007, -3/+4so basically glass has viscosity....a quality of liquids, but it still isn't a liquid?
      • ChemEng, on 10/10/2007, -2/+6*sigh*
        Its not worth the space pointing out the errors in this argument.
      • Bdog2g2, on 10/10/2007, -0/+7its an amorphous solid, meaning it does not have a true regular crystalline structure. Basically the crystals are heterogenous in size and will not lock into place with others in a regular pattern.
      • smackhero, on 10/10/2007, -0/+2from what i can gather, it seems that glass doesn't form crystal lattices like other solids, but it also doesn't sit comfortably in confined spaces the way liquids do. it's sort of a grey area, so researchers are trying to determine whether there is a hidden structure that explains glass' physical properties.

        however, your example of glass windows in old churches is incorrect as others have already explained. it would be impossible for glass to demonstrate such obvious liquid qualities in such a short time.
      • asteron, on 10/10/2007, -0/+1Alluminum has a viscosity.

        Glass actually has a higher one.
    • norman619, on 10/10/2007, -5/+3The definition of a liquid:

      Liquid: The state of matter in which a substance exhibits a characteristic readiness to flow, little or no tendency to disperse, and relatively high incompressibility.

      This pretty much describes glass. Glass is a very slow moving liquid.
      • jackhole, on 10/10/2007, -0/+1That also perfectly describes a handful of soft ferrite shavings, among other things. That doesn't make ferrites liquid.
      • asteron, on 10/10/2007, -1/+3Glass does not flow at room temperature. Thus your definition will characterize it as a solid.
    • tehpwnrate, on 10/10/2007, -0/+1Glass never undergoes the transition to a frozen or solid form. As water ice is heated, it stops at 0* C and hangs there while you continue to put energy in--this is the ice melting--and then once it's a liquid, it keeps heating up again. Glass just keeps on heating, as it has never become a "solid" and thus never has to transition to a liquid. It acts like a solid, but over time there IS evidence of it being a liquid.
      • asteron, on 10/10/2007, -0/+1What evidence? All experiments say otherwise.
    • johney5, on 10/10/2007, -0/+0lol, your kidding? hes kidding, right?
  • Error601, on 10/10/2007, -3/+3That wouldn't be a good test anyway, since you can distort any solid with force. It's either going to change shape or come apart. The coins in your pocket are a good example of how the metal was forced to flow.

    • jmkiii, on 10/10/2007, -0/+2Only if it is brittle. If it is malleable, you can manipulate it's shape with force.
    • asteron, on 10/10/2007, -0/+7From wikipedia

      "A myth does exist that glass rods and tubes can bend under their own weight over time. To test this, in the 1920s, Robert John Rayleigh, son of the Nobel Prize winner John William Rayleigh, conducted an experiment on a 1 metre (~39 in) long, 5 millimetre (~3/16 in) thick glass rod, which was supported horizontally on two pins with a 300 gram (~0.66 lb) weight in the middle. Apart from the initial bending of 28 millimetre (~1.1 in), the position of the weight did not change until the end of the experiment, which lasted for 7 years. At the same time, another man, a worker of General Electric named K. D. Spenser, conducted a similar experiment independently. Two months after Rayleigh, he published his own results which also disproved the myth. Spenser suggested that the myth was composed before the 1920s, when the tubes were made by hand, and naturally some of them were curved to begin with. Over time the straight tubes were taken away, and only the curved ones remained. Some people probably thought it was the glass flowing."
  • str3ama, on 10/10/2007, -18/+3I heard long ago that it was a slow moving liquid, but this can be easily disproven, since if I put a glass jar in a tray and just leave it there - if I were to come back in a million years (assuming nothing happens to the jar and tray), the glass will still be glass and not a pool of liquid.
    • Cerialthriller, on 10/10/2007, -1/+9i dont know about the timeline, but eventually over a long enough timeline, the theory is that the glass will not hold the original shape, even if only fractions off, even in a completely erosion free environment
      • yojiffyskippy, on 10/10/2007, -0/+2I'm going to do this experiment starting today. Set a reminder on you calendar to check back in August 10th, 1002007.
    • IanCal, on 10/10/2007, -2/+19"but this can be easily disproven, since if I put a glass jar in a tray and just leave it there - if I were to come back in a million years (assuming nothing happens to the jar and tray), the glass will still be glass and not a pool of liquid."
      It can be easily disproven by assuming it's not true? Good circular reasoning there
    • IanCal, on 10/10/2007, -11/+3"but this can be easily disproven, since if I put a glass jar in a tray and just leave it there - if I were to come back in a million years (assuming nothing happens to the jar and tray), the glass will still be glass and not a pool of liquid."
      It can be easily disproven by assuming it's not true? Good circular reasoning there
    • nodonoug, on 10/10/2007, -1/+4Can you cite an experiment proving this?
    • Cykaos, on 10/10/2007, -1/+5Haha.. How is it easily disproven? Have you actually put a glass jar in a tray and then left it there for a million years? I would thinking running an experiment over a million years would be very hard to prove or disprove.
    • smackhero, on 10/10/2007, -1/+4oh yea, just put a glass jar in a tray and come back in a million years--that experiment would be _so easy_ to conduct. why didn't those scientists think of this before?

      you sound like a creationist matter-of-factly spouting off unscientific theories and assumptions about things they're completely ignorant about. how do you _know_ what the end result of such a experiment would be?

      luckily real scientists don't just come up with unscientific experiments that are absolutely impossible to conduct, make up the results to said experiments based purely on what they imagine would happen as if it were simply common sense, and then smugly act as though they've just soundly proven a scientific fact.

      you're an absolute idiot. did you even bother reading the article before commenting or do you just like babbling nonsense like a retard?
  • Cerialthriller, on 10/10/2007, -16/+10I learned in chemistry years ago that glass was a super-cooled liquid. Its easy to see in very old windows that they get wavy and it looks like water running down a window at an incredibly slow rate.
    • altgeeky1, on 10/10/2007, -0/+5>Its easy to see in very old windows that they get wavy and it looks like water running down a window at an incredibly slow rate.
      No, that's different: you are referring to "leaded glass". Pre-modern glass contained lead - that and production methods caused the 'wave' effect you see.
      You can see the same effect in antique stained glass.
      http://en.wikipedia.org/wiki/Lead_glass

      Now I am not commenting one way or the other on the article... just your 'it's very easy to see..' comment.
    • Davedave, on 10/10/2007, -2/+9gee, couldn't be because old methods of glass manufacturing resulted in less precise panes? or that people were smart enough to put the thicker side of a piece of glass downward for stabiliy... and the glass artifacts we have from thousands of years ago that have somehow NOT melted into a puddle over the time are just a fluke.

      your chemistry teacher was a moron.
      • Viper323, on 10/10/2007, -1/+1Thanks for typing up exactly what I wanted to say :D
      • Subliminational, on 10/10/2007, -3/+1That's no reason for such a mean spirited response! You can tell someone they're incorrect without being so caustic.
      • Cerialthriller, on 10/10/2007, -2/+1where did i say anything about it being thicker? Old glass many times looks like running water frozen in place, which were not like that when installed. Please quote where i mention the thickness of the glass anywhere
        • LonesomeFighter, on 10/10/2007, -0/+1it was another person before you. Davedave just decided to comment on multiple people's retardation in one comment.
    • Richman777, on 10/10/2007, -1/+8As with so many other people who have posted this, your chem teacher was wrong. That was due to manufacturing. Dear god, read the comments.
    • Tgg161, on 10/10/2007, -1/+8Myth myth myth. I can't believe people are digging the window 'evidence'.
      http://math.ucr.edu/home/baez/physics/General/Glass/glass.html
  • weekapaug81, on 10/10/2007, -12/+16yeah thanks 8th grade science class circa 1992.
    • smackhero, on 10/10/2007, -0/+7let me guess, your science teacher misinformed you about glass window panes in old churches like the other 20 morons have already commented above?
  • jontymisra, on 10/10/2007, -8/+1This isnt something new, learnt about this back in India over 5 years ago.
  • snarkleclackers, on 10/10/2007, -9/+3Anybody else catch that pun? "Physicist opens new *window* on glass puzzle". Eh? Eh? I don't think it counts though, because he failed to mention that it was either intentional or unintentional. Minus 5 points.
    • snarkleclackers, on 10/10/2007, -0/+0Damn. I can't believe I didn't notice that that joke had already been made. And to think, I'm always getting really ticked at the people who make the same joke twice... Minus 5 points.
      • MK0094, on 10/10/2007, -0/+0I hate you both. minus infinity points.
        • snarkleclackers, on 10/10/2007, -0/+0"you both" is the same person.
  • Bando, on 10/10/2007, -1/+3http://72.14.253.104/search?q=cache:wGOw7NiszuAJ:www.emory.edu/EMORY_REPORT/erarchive/2007/July/July%252023/S%26RWeek.htm+glass+solid+or+liquid+emory&hl=en&ct=clnk&cd=1&gl=us&client=firefox-a
  • bsolidgold, on 10/10/2007, -15/+10Slow moving liquid.

    Moving on...
    • briguymaine, on 10/10/2007, -2/+5Glad I'm not the only one who knew this. Isn't this basic info?
      In college, one of my roommates said that hot water would freeze faster than cold water, huh?
    • gwhardyiv, on 10/10/2007, -0/+4Did you even bother to read the article? The headline totally misses the point.
  • flukierdonut, on 10/10/2007, -5/+4yeah ok this is not anything new at all
  • superbad, on 10/10/2007, -3/+6Glass obviously exists in a solid/slow-moving liquid duality.
    • 10001, on 10/10/2007, -1/+11you should have stopped after the third word
  • binaryis4lovers, on 10/10/2007, -11/+6This is so stupid. I've known this since middle school.
  • Bipedal, on 10/10/2007, -5/+24The reason older glass is thicker at the bottom is because of the way sheets of glass used to be made. They would put the molten glob of glass on a sort of spinning disc and let it flatten out. this caused the edges to be thicker, so they put those on the bottom for strength. There are even examples of things like churches and older buildings where the windows were put in upside-down, so the thick part is at the top. Distorted glass isn't a good way to prove the 'liquid' bit of the argument.
    • smackhero, on 10/10/2007, -0/+8and yet there are at least 20 morons in this discussion saying how they learned that glass is liquid in grade school, repeating that fallacious argument.

      even if you simply "knew" that glass is a slow moving liquid--which is still a debated grey area--these scientists are researching the yet unknown reason why it exhibits these physical characteristics. unless you have the answers, don't be a smart ass.
      • NJank, on 10/10/2007, -0/+2and if there are 20 digg morons, how many more people in the world are misinformed. dear god, the humanity...
    • PhilH, on 10/10/2007, -0/+1Bipedal is right. I heard this exact explanation on Q.I. once, and we all know that Stephen Fry is never wrong.
  • JJsays, on 10/10/2007, -9/+2How dose light travel at the speed of light?
  • myranttoyou, on 10/10/2007, -15/+6I did not RTFA, but as a degree holder in physics you learn it is a fluid right away. This is not new info.

    Fluid = Anything that flows. Glass does flow slowly.

    Look at very old windows, the bottom thickness is larger than the top. This is less obvious in newer construction, but it still holds.
    • Tgg161, on 10/10/2007, -2/+9You learned wrong! Windows are not 'thicker on the bottom' -- it's a myth.
      http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

      You may call glass 'liquid' if you want, since it has molecular structure different from most solids, but stop perpetuating the window myth as 'proof'.
      • myranttoyou, on 10/10/2007, -7/+2A link will not disprove what I've seen in person. I've seen glass in this state.

        Also, one fact does not preclude another.

        Being a fluid does cause this, how much is up to bored physicists to determine.
      • noisey, on 10/10/2007, -4/+2great link. I learned a long time ago that glass wasn't a liquid. But the idea is so cool many people still spread that myth.
        • Subliminational, on 10/10/2007, -0/+1in the link however it says that either a liquid or solid interpretation can be justified
    • DeeprBlue, on 10/10/2007, -2/+7Degree holder in physics, my ass.
    • catalysis, on 10/10/2007, -2/+7No, it doesn't hold. That is a myth which has been thoroughly debunked.
    • Richman777, on 10/10/2007, -1/+5I guess being a Physics major they didn't teach you that this is Chemistry. You'll argue that it has to do with physics but molecular structures is all chemistry. Go watch some planets rotate.

      Also the whole bottom is thicker than at the top has been debunked a LONG LONG LONG time ago and is attributed to manufacturing processes of the time. Stop citing that as proof.
    • Frothy, on 10/10/2007, -1/+6Physics degree revoked! The thickness of very old windows are proof of nothing except the method of their manufacture.
      http://www.sciencenews.org/pages/sn_arc98/5_30_98/fob3.htm
      • FrothyA, on 10/10/2007, -0/+0Whoa! Another Frothy! But I'm older!
    • Cykaos, on 10/10/2007, -1/+7as a degree holder in physics you should know that the thickness of glass windows over a few hundred years has nothing to do with glass being a liquid but more to do with manufacturing style.
      • Richman777, on 10/10/2007, -0/+3Or the fact that it has nothing at all to do with physics.
    • mstoneburner, on 10/10/2007, -1/+4Did you get your degree out of gum ball machine?
    • smackhero, on 10/10/2007, -1/+3wow, where did you get your degree from? cuz i sure as hell don't want my kids to study there. read the comment above, and the 20 other comments explaining why that example is absolute nonsense.

      stop being a troll and RTFA before you comment.
    • unin5pired, on 10/10/2007, -0/+1As a degree holder in physics at a respected university who actually does materials research, I assure you that 1- you didn't learn to properly read a scientific article, and 2- you clearly had a rotten education.
  • mrgodai, on 10/10/2007, -0/+2http://www.eurekalert.org/pub_releases/2007-08/eu-epo080907.php
  • kuwan, on 10/10/2007, -3/+47I'll smack you on the head with a glass bottle and you can tell me whether it's a solid or a liquid.
  • over9, on 10/10/2007, -8/+7will a plane on a treadmill take off?
    • EXreaction, on 10/10/2007, -1/+11Is there anyone stupid enough to believe it wouldn't?
      • GMorgan, on 10/10/2007, -3/+2Well it depends on the apparent velocity between the air and the wing surfaces. The real question is if the effect of the treadmill dragging the air is enough to generate the lift required for take off.
        • Subliminational, on 10/10/2007, -1/+1exactly, its the relative velocity of the air as seen by the plane's wings (or the wings as seen by the air!) that matters
      • AdamFromMyspace, on 10/10/2007, -5/+3You guys are retarded. Plans aren't propelled by their wheels, but by the turbines in their wings.. it would fly off the front of the treadmill.
    • kelpdip, on 10/10/2007, -1/+11What about a plane on a stairmaster?
    • 10001, on 10/10/2007, -0/+1only in a forest
    • grimjestor, on 10/10/2007, -5/+3if your hypothetical treadmill was always able to exactly match the plane's ground speed, it would never take off, because there would be no air flow around the wings to provide lift...
      • Ramble, on 10/10/2007, -2/+2Naw. For your argument to work the wheels would have to be providing power to the ground. That is not how an aircraft works. The engines on the wing force air out of the back that pushes it forward.
    • Ibox, on 10/10/2007, -5/+3No, there wouldn't be enough lift.
    • postitnote, on 10/10/2007, -3/+2If you believe that a water plane can take off, then you should believe a regular plane can take off on a treadmill.
    • puddleboy, on 10/10/2007, -2/+1grimjestor / lbox:

      The plane would certainly be able to take off.

      Think of it like this: Let's say I have a toy car with a string on the front of it. I can pull this car around on the ground with the string. I then set the car on a treadmill. I hold on to the string so the car is pulled back by the treadmill. Eventually, the whole system is stationary except for the wheels and the treadmill: I am holding the string, the string is attached to the car, the car wheels are spinning and the treadmill is moving.

      Would it be much more difficult for me to pull the car forward with the string since is is on this treadmill? No, not much at all.

      The plane situation is very similar. Instead of 'pulling' the plane, we are pushing it (jets against the air). The wheels are there to remove friction only, not to push the plane forward. The plane would move forward very similarly to the way it would move forward if it were on a stationary runway (with just a slight increase in friction) and would take off normally, though I suppose a plane taking off on a treadmill runway could rarely be classified as normal.

      -Puddleboy
      • Ibox, on 10/10/2007, -0/+1the wheel motion of the wheels have nothing to do with anything, the reason an air plane goes along a runway is to get up enough speed "through the air" to generate the required lift to take off. you would get no lift sitting still on a treadmill. If anyone donsent believe me then why don't they put huge treadmills on aircraft carriers?

        -IBOX
      • Ibox, on 10/10/2007, -0/+1Sorry Puddles, just realized my retardation... the plane would still move forward, Its amazing how a couple beers clear things up.
    • UlicBelouve, on 10/10/2007, -0/+1No, it wouldn’t. There are four forces at work here: Lift, Weight, Thrust, and Drag. Due to Bernoulli's Principle, lift is created as the airflow is deflected by an airfoil or other body. The force created by this acceleration of the fluid creates an opposing force to weight. The engines on the wings provide thrust, not lift. This thrust contributes to airflow, which through Bernoulli's Principle creates lift, but only when it is moving through the air.

      By your theory, a plane that is chocked (wedges keeping the wheels in place) would suddenly take off when the propellers are geared up as part of the pre-flight checklist. It generates a lot of thrust, but since no airflow, no lift. You won’t get a kite to take off if it is not moving through the air either. It needs airflow for lift. (Kites also follow Bernoulli's Principle)

      My brother has a pilot's license, and my father is a commercial airline pilot.

      I can’t see how the people who are giving the correct answer are being dugg down.
      • puddleboy, on 10/10/2007, -0/+1The point you are missing is that even though the treadmill is going the opposite direction of the plane, the plane will still move forward.

        The wheels are not creating the thrust here. If the treadmill matches the ground speed of the plane perfectly, the wheels will spin 2x the groundspeed of the plane. If it were a motorcar, the motorcar would move 0 mph relative to the non-treadmill ground because the wheels are what create the forward motion. The wheels on a plane do NOT create forward motion and are present only to reduce friction between the plane and the ground.
    • kelpdip, on 10/10/2007, -0/+2Wrong UB.
      Let's switch your scenario around for a second. Plane is chocked, wheels stay stationary. Instead of the treadmill you will have the AIR blow past it, wind-tunnel style. The plane would take off without moving forward then because lift is a function of AIRspeed.
      The only issue with a treadmill takeoff is that the wheels would be trying to roll faster than the plane's takeoff airspeed, which they might not be designed for.
    • kelpdip, on 10/10/2007, -0/+2Wait, i see what is going on here, there are 2 different physics problems being discussed.
      Giant treadmill:
      A plane would be able to take off from a runway-sized treadmill because ground speed has no effect on aerodynamics and the engines are fighting aero drag, not wheel drag.
      Plane-sized treadmill:
      Won't work, need the wind to move across the wings, not the ground beneath the wheels.
      My mistake UB.
  • MBHoy, on 10/10/2007, -3/+3*chases a stray window*
  • nesibus, on 10/10/2007, -4/+2let me know when this slow moving liquid of shattered glass on the floor....combines all back together into a puddle.
    • SkippyDoorknob, on 10/10/2007, -0/+3It will combine back together, but only if you say "hasta la vista, baby" before shattering it.
  • popstop785, on 10/10/2007, -5/+0Glass is a liquid.
  • DaJokerInU, on 10/10/2007, -1/+15I'm pretty sure that glass is an amorphous solid.

    http://en.wikipedia.org/wiki/Amorphous
    • Travisty2012, on 10/10/2007, -0/+2According to my high school physics / chemistry teachers...it is. That's what I was taught in high school anyway...
      • nmathew, on 10/10/2007, -0/+2According to my advanced statistical mechanics course in grad school it is as well.
    • 10001, on 10/10/2007, -0/+1that lack of certitude is aptly attributed to wikipedia
    • davidrools, on 10/10/2007, -0/+1thank you, dajokerlnU. There is so much retarded information on this thread. material science texts confirm your high school studies, Tavisty. Amorphous solid ftw. end of discussion.
      • SillyRabbits, on 10/10/2007, -0/+1A general material science text doesn't cover glasses in enough detail to address what they are discussing in this research. Like most of what they teach in material science, it's only a part of the story and generally only applies to idealized cases. In real systems things become much more difficult.
  • monomyth, on 10/10/2007, -8/+2this is something kids in the 3rd world countries learn in school.
  • OutThisLife, on 10/10/2007, -0/+22Is this host dead or merely an extremely slow-moving server?
    • Telxon, on 10/10/2007, -2/+2Slow like glass....
      • stupergenius, on 10/10/2007, -1/+1Haha, oh now that is comedy. That belongs in a Family Guy episode. Dugg^2.
  • LordSlashstab55, on 10/10/2007, -9/+0of course it's a slow moving liquid, just look at old windows, they bubble down, and appear distorted
    • norman619, on 10/10/2007, -0/+2Not appear distorted. They ARE distorted.
  • SaII, on 10/10/2007, -6/+2I bet that glass liquid'll be really hot
  • Richman777, on 10/10/2007, -6/+3For everyone saying "DUH" to this, we already know that it is in fact a slow-moving liquid. The article clearly states that when it is cooled, it never forms a lattice structure. This article simply reinforces that. You can never have too much proof.
    • DeeprBlue, on 10/10/2007, -0/+4Just because it doesn't form a lattice structure doesn't mean that it's a slow-moving liquid. Glass challenges the notion that you need to have crystalline structure to have a solid. Hence why it's an amorphous solid. And if you bothered to read the article, they test to see how small one can make glass before it no longer exhibits characteristics of a solid.
  • madtaco, on 10/10/2007, -3/+9FTA: "Weeks has devoted his career to probing the mysteries of "squishy" substances"....."they include everyday substances such as toothpaste, peanut butter, shaving cream, plastic and glass"

    Wife: "How was work today, honey?"
    Weeks: "Not bad, the peanut butter and shaving cream are proving to be a little trickier than we had first thought."
    Wife: "You want some nachos?"
  • mijoe, on 10/10/2007, -9/+1This guy has spent his career to stumble upon the long known fact that glass is an amorphous solid? (http://en.wikipedia.org/wiki/Amorphous) You can see this process when visiting old forts... there are small gaps at the top if the glass panes in the frames sometimes, since the glass is slowly creeping down...
    • asteron, on 10/10/2007, -1/+4Or it was installed like that or the metal hinges in the frame are rusting.
    • unin5pired, on 10/10/2007, -0/+1The relevance of the article is not that glasses are amorphous.
    • kazem, on 10/10/2007, -0/+1Try reading the article. And try knowing a little about a subject before you open your mouth to talk about it. Have you ever thought that studying material properties might be important if we plan on making more advanced materials?
  • triad203, on 10/10/2007, -2/+16"Is glass a solid or merely an extremely slow-moving liquid?"

    Yes.
  • edrainkona, on 10/10/2007, -4/+1I don't know, but glass is broken when it is dropped from a height.
  • tacklebox, on 10/10/2007, -3/+7Its been proven a solid. The theory of old glass being wavy therefore its a liquid, has 100% to do with the way they used to make glass, not with any "flowage" of glass molecules.
  • katieisafighter, on 10/10/2007, -1/+0seriously, my 5th grade science teacher will be glad to hear this. perhaps they could use the term amorphous until a better defintion comes along.
  • ghindo, on 10/10/2007, -1/+5Why does this remind me of discussions on 4chan?

    Wood is a liquid.

    http://img514.imageshack.us/img514/2200/woodisaliquidyv7.png
  • norman619, on 10/10/2007, -7/+1This is old news. Glass is a very slow moving liquid. If you look at old windows you will find that the glass is thicker at the bottom than on top. Not by design. The glass slowly flowed to the bottom.
    • asteron, on 10/10/2007, -0/+2Glass does not flow in any sense. Think about the perfect glass they find in egyptian tombs. Have you ever seen a puddle of glass?

      A myth does exist that glass rods and tubes can bend under their own weight over time. To test this, in the 1920s, Robert John Rayleigh, son of the Nobel Prize winner John William Rayleigh, conducted an experiment on a 1 metre (~39 in) long, 5 millimetre (~3/16 in) thick glass rod, which was supported horizontally on two pins with a 300 gram (~0.66 lb) weight in the middle. Apart from the initial bending of 28 millimetre (~1.1 in), the position of the weight did not change until the end of the experiment, which lasted for 7 years. At the same time, another man, a worker of General Electric named K. D. Spenser, conducted a similar experiment independently. Two months after Rayleigh, he published his own results which also disproved the myth. Spenser suggested that the myth was composed before the 1920s, when the tubes were made by hand, and naturally some of them were curved to begin with. Over time the straight tubes were taken away, and only the curved ones remained. Some people probably thought it was the glass flowing.
  • DeeprBlue, on 10/10/2007, -1/+6Wow. Digg is becoming ugly. If people even bother to read the article, it really has nothing to do with "solving" the puzzle of glass being a liquid or a solid. It's a very interesting read, because they explain their technique of examining how glass becomes "glassy" since the phase change isn't obvious. Instead, most of the commenters here are preoccupied with showing off their knowledge when really, no one asked their "expert" opinion on the subject.
  • jacekw, on 10/10/2007, -4/+2Buried for a stupid title and description. I think I learned in... oh say... sixth grade.. that glass had some sort of duality to it. Wavy glass has nothing to do with it either. If it were a liquid, you would see the top thin and the bottom thicker... not waves.
  • h3x1lu2, on 10/10/2007, -7/+0holy crackers...have you people never heard of super cooled liquids before? they teach you this stuff in a basic high-school chemistry or physics class these days.
    • DeeprBlue, on 10/10/2007, -0/+3Yeah, and it's all been debunked. A supercooled liquid is a liquid that has been cooled below its freezing point but still retains all the same properties it had as a liquid. Glass is NOT one of them. It's an amorphous solid.
  • rhodesman, on 10/10/2007, -7/+0um dude yeah I learned about this is High School.
  • jackspratmich, on 10/10/2007, -1/+7Seriously guys, please educate yourself before commenting on these things. Glass in the old days was made by stretching the molten material then cooled. When you stretch liquid glass it ends up being distorted, because you cannot do it uniformly. Current technology uses liquid tin which the molten material is pulled over very slowly allowing the glass to be uniformly thick and flat on both sides. Go to a glass manufacturing plant and take a tour. It is quite amazing. As far as glass being a liqud or solid according to physics, I don't know, but no glass changes it's shape over time naturally. The windows in old churches looks exactly like it did when it was made aside from some normal wear over time.
    • Andysan, on 10/10/2007, -0/+1Good post. Most other comments prove that U.S. science education is in big trouble.
  • jiminizer, on 10/10/2007, -3/+1errrr i remember this coming up when we stuudied solids liquids and gasses in year 6 (UK) or what i'd immagine you call 6th grade (about age 11 anyway) buried as lame,
    • noahhoward, on 10/10/2007, -0/+1It's fitfh grade in the states, they start at K then 1, 2, 3, 4...
  • SlowOnTheUptake, on 10/10/2007, -0/+3Here's an example of a highly viscous, slow-moving liquid: http://en.wikipedia.org/wiki/Pitch_drop_experiment
  • noahhoward, on 10/10/2007, -0/+5It was an Amorphous Solid 5 years ago when I started my physics degree.
    • nmathew, on 10/10/2007, -0/+1As it was when I started my physical chem Ph.D. program, which was also 5 years ago. Do'h!
  • AaronCSU, on 10/10/2007, -1/+16Engineering grad student here, this is an old debate.
    Glass is an amorphous solid. That means it has no crystal structure. It also has no precise melting point. You may often seen a melting point given for glass but this is simply a temperature where the glass flows easily. As you lower the temperature it will simply become more and more viscous until it is essentially a solid. A crystalline solid has a distinct melting point where the crystal structure suddenly breaks down. The question is does glass ever actually become solid, or does it still flow, just very slowly.

    Many people point to old windows that are thicker on the bottom as proof of glass flowing. As I understand it this has been well debunked. Old panes of glass do not have uniform thickness due to manufacturing methods used then and you will very often see panes that are thicker on the top. Plus if glass flowed quickly enough that a piece of it just 100-150 years old displayed measurable deformation there would be no debate, that would be an easy to measure viscosity. Plus tempered glass would not be possible. I will not get into a discussion of how tempered glass works but suffice to say it would not function for decades, as it currently does, if the glass was flowing at that rate.

    My best assessment is that, for all intents and purposes, glass is a solid. It has no measurable deformation over centuries. While its' viscosity may not be infinite it has to be so high that one could assume it is infinite. Of course I am an engineer, we always look at things this way, physicists may not like this answer.
    • AaronCSU, on 10/10/2007, -0/+2Just to add some more data to this. Romans were making glass objects 2000 years ago. The Portland Vase was made in the first century and doesn't show any signs of "flow" There are stained glass windows that date back to the 10th or 11th century. Some people claim they show signs of deformation, but there is actually nothing about them that would indicate they have flowed, like forming into or around depressions in their frames, etc. This should just add more evidence that glass does not show evidence of flow on timescales of several centuries, or millenia even.
  • akatherder, on 10/10/2007, -3/+1I always knew my high school chemistry teacher was ***** me! I'll admit that I don't grasp the difference between glass and ice (for example) at a molecular level. I just can't rationalize glass being a liquid based on its physical properties. You can't shatter a liquid. I don't feel like I'm drinking a liquid out of another liquid when I am having a pint/bottle of beer.
    • hokieaudi, on 10/10/2007, -0/+3The difference is how the individual atoms which make up the material are arranged. In water ice the arrangement of hydrogen and oxygen atoms is very well defined and can be measured with a high degree of precision. Knowing the position of one water molecule you may calculate the position of other molecules based on the way in which the solid structure repeats itself. Glass is an amorphous material, meaning it was no regular crystalline structure. This amorphous condition exists even at very low temperatures (when glass is solid). This lack of crystalline structure as Aaron correctly points out above is one of the definitions of a liquid which is why this thought experiment is so interesting.
    • asteron, on 10/10/2007, -0/+2Glass is amorphous like a liquid's molecular structure but does not flow. The definition that best suits it is an amorphous solid.
  • HanSolo69, on 10/10/2007, -3/+3anyone ever heard of an amorphous solid? because..you know..that's what glass is....and they've known that for a loooong time.
  • 9a3eedi, on 10/10/2007, -1/+4I say it's soliquid
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