Glass is Solid, Not Liquid: Urban Legend Debunked

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Discussion Overview

The discussion revolves around the classification of glass as either a solid or a liquid, exploring the definitions and properties that contribute to this debate. Participants examine historical beliefs, scientific definitions, and the physical behavior of glass over time, with references to both theoretical and practical implications.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that glass is a solid, noting that it retains its shape and does not flow over short timescales.
  • Others argue that glass can be considered a highly viscous liquid or an amorphous solid, depending on the definitions used.
  • A participant mentions that the bottom of old glass panes is thicker due to historical manufacturing processes, suggesting this is a myth about glass flowing over time.
  • There is a discussion about the nature of liquids and solids, with some participants questioning whether the definition of a liquid as something that takes the shape of its container is sufficient.
  • Some contributions reference the glass transition and the behavior of materials under stress, indicating that glass can deform slowly under certain conditions.
  • Participants discuss the implications of viscosity and the potential for glass to flow over extremely long timescales, with some suggesting that this is a semantic issue rather than a strict classification problem.
  • References to experiments and historical examples are made to illustrate points about the properties of glass and its classification.

Areas of Agreement / Disagreement

Participants express differing views on whether glass should be classified as a solid or a liquid, with no consensus reached. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

The definitions of liquid and solid are noted to be loose and dependent on context, with some participants highlighting the limitations of these definitions in relation to glass and other materials.

Who May Find This Useful

This discussion may be of interest to those studying materials science, physics, or engineering, as well as anyone curious about the properties of glass and the nature of states of matter.

jobyts
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Since my high school days, I learned that glass is a liquid. (Science naive students thought glass is solid, and the smarty pants knew it was actually a liquid:) Yesterday, while I was telling this interesting fact to my daughter, my wife argued that glass is solid. I googled to explain them why glass is a liquid, but apparently science web sites points out that "glass is liquid" is an urban legend. Seems like I was wrong all these years. I thought of posting this here because some people here might be thinking glass is a liquid.
 
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How you define "liquid" is the important question to ask. Depending on your definition, it can be either a liquid or solid.

If you had a 100 year old glass pane, and you measured the top and bottom, you'd find that the bottom would be slightly thicker.
 
jobyts said:
I googled to explain them why glass is a liquid, but apparently science web sites points out that "glass is liquid" is an urban legend. Seems like I was wrong all these years.

Idk, jobyts. Looks like the jokes on you...:redface:
 
Astrum said:
If you had a 100 year old glass pane, and you measured the top and bottom, you'd find that the bottom would be slightly thicker.
That's what all the web sites say as a myth. They designed the glass pane bottom thicker for stability.

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html
 
liquids take the shape of their container. Glass doesn't.
 
Physics_UG said:
liquids take the shape of their container. Glass doesn't.

Is water liquid at zero gravity?
 
jobyts said:
That's what all the web sites say as a myth. They designed the glass pane bottom thicker for stability.

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

It might be a myth, I've never tried it myself :-p, but it claims on the bottom exactly what I mentioned in my first post.

In terms of molecular dynamics and thermodynamics it is possible to justify various different views that it is a highly viscous liquid, an amorphous solid, or simply that glass is another state of matter that is neither liquid nor solid. The difference is semantic
 
jobyts said:
Is water liquid at zero gravity?

Are you serious? Tell me you haven't seen the NASA videos with the guys sucking liquid water/juice balls out of mid-air on the space station, etc.. Those are liquids, it's just the surface tension that makes them look like balls. As Physics_UG pointed out, you can see the balls morph as if they would take the shape of their container.
 
We had a long, long thread about this a few years back. For all intents and purposes, glass is a solid. It won't flow over the course of a few hundred years. However, by some strict technical definition, according to former mentor, Gokul90210, it is often classified as a liquid. You might see some flow over billions of years.
 
  • #10
DiracPool said:
Are you serious? Tell me you haven't seen the NASA videos with the guys sucking liquid water/juice balls out of mid-air on the space station, etc.. Those are liquids, it's just the surface tension that makes them look like balls. As Physics_UG pointed out, you can see the balls morph as if they would take the shape of their container.

Can you please point me to a video? Searching with the keywords (guys sucking liquid water/juice balls) you mentioned points me to weird videos :)

Unless there is an external force (gravity or something else) to overcome the surface tension, any matter would retain its shape. In this case, before the sucking action by the astronauts , was the water ball liquid or solid? Given enough force, most (if not all) solids could become liquids.

As mentioned before (by Astrum), the definition of liquid/solid is a loose one, and assumes normal forces acting upon them. (as Earth's surface gravity). A definition for liquids as it takes-the-shape-of-container is not complete. With that definition, a freely falling rain drop (with no other external forces on it) is not a liquid.
 
  • #11
jobyts said:
Can you please point me to a video? Searching with the keywords (guys sucking liquid water/juice balls) you mentioned points me to weird videos :).

How about this one?

https://www.youtube.com/watch?v=4o1lr9LxODc
 
  • #12
DiracPool said:
How about this one?

Thanks Dirac :)
 
  • #13
Or this one:

https://www.youtube.com/watch?v=s63JXdsL5LU
 
  • #14
This is related:

http://en.wikipedia.org/wiki/Pitch_drop_experiment

It is a matter of viscosity. Very high viscosity makes us think about tar as of a solid, yet given enough time it flows. I am not sure if the glass will flow at the room temperature - at least not in typical timescales, at least not all glass types - but the same reasoning applies.

Basically we are trying to apply separate names to a continuous reality that doesn't care about our definitions.
 
  • #15
jobyts said:
Is water liquid at zero gravity?

It depends on its temperature, just like when it is on earth.
 
  • #16
jobyts said:
Since my high school days, I learned that glass is a liquid. (Science naive students thought glass is solid, and the smarty pants knew it was actually a liquid:) Yesterday, while I was telling this interesting fact to my daughter, my wife argued that glass is solid. I googled to explain them why glass is a liquid, but apparently science web sites points out that "glass is liquid" is an urban legend. Seems like I was wrong all these years. I thought of posting this here because some people here might be thinking glass is a liquid.
It's an amorphous solid. Generally it retains it's shape. Under pressure/stress, glass and ceramics (e.g., concrete) will deform/creep very slowly.
 
  • #17
Materials that are commonly referred to as 'glass' are disordered solids. Glassy materials include colloids, foams, emulsions, granular materials, and are characterized by dramatic changes to macroscopic properties (viscosity) without corresponding changes to microscopic properties (structure) as the 'glass transition' is approached.

The nature of the glass transition is not completely understood.
 
  • #18
jobyts said:
Is water liquid at zero gravity?
Er, that question implies you are talking about water floating in a ball in the middle of the space station, not in a container. But how do you think it got there!
 
  • #19
jobyts said:
That's what all the web sites say as a myth. They designed the glass pane bottom thicker for stability.

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

To add to this, I live close to Strawbery Banke (not a typo), where some of the oldest original windows in the country are still in use. The process that made glass windows in the 1600s left one side thicker than the other (unintentionally), window installers would simply place the thicker side on the bottom for stability. The taper itself, however, was not intentional just a byproduct of the spinning that was done to make the pane as smooth as possible. The best windows were considered to be the ones that had the least taper to them and were, therefore, more distortion free.
 
  • #20
Glass is neither solid nor liquid. It's all an illuminati plot.
 
  • #21
Astronuc said:
It's an amorphous solid. Generally it retains it's shape. Under pressure/stress, glass and ceramics (e.g., concrete) will deform/creep very slowly.

yup, just like the crust of the Earth does. Ductile deformation.
tho if "pushed" too hard and fast we will see brittle deformation mode, fracturing/shattering, just as with glass

Dave
 
  • #22
It's good that glass in ultra-precise optical instruments doesn't "run" very much.

Which brings to mind that 100 year-old glass that was ground and polished to extreme accuracy could be remeasured to see if anything changed. If no change, stick it on a shelf for a couple hundred years and check it again...
 
  • #23
Oldfart said:
It's good that glass in ultra-precise optical instruments doesn't "run" very much.

Which brings to mind that 100 year-old glass that was ground and polished to extreme accuracy could be remeasured to see if anything changed. If no change, stick it on a shelf for a couple hundred years and check it again...

true, but I suspect the effect would be only really noticeable on much larger and thinner sheets of glass, rather than on say ... lenses etc an inch or so thick and maybe a few inches in diameter


Dave
 
  • #24
Last week a Phys. Rev. Lett. was published revealing more about the nature of glass and bringing it closer to solids. Here is a link for the highlight of the article:

http://physics.aps.org/articles/v6/60
 
  • #25
davenn said:
true, but I suspect the effect would be only really noticeable on much larger and thinner sheets of glass, rather than on say ... lenses etc an inch or so thick and maybe a few inches in diameter


Dave

Prehistoric obsidian cutting implements are still sharp- is >10k years enough time for you?
 
  • #26
Try http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.uAlberta.ca/~bderksen/florin.html
 
Last edited by a moderator:
  • #27
From my Themrodynamics book (by Engel), "Glasses are liquids of such high viscosity that they cannot achieve equilibrium on the timescale of a human lifetime."

It's not a very good book, though, so I probably wouldn't take his word for it.
 

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