It is said that glass in old churches is thicker at the bottom than at the top because glass is a liquid, And so over centuries it has flowed towards the bottom. This is not true. In Medieval times panes of glass were often made by the Crown glass process. A lump of molten glass was rolled, blown (Like we do in runescape ), expanded, flattened and finally spun into a disc before being cut into panes. The sheets were thicker towards the edge of the disc and were usually installed with the heavier side at the bottom. Other styles of forming glass panes have been used but it is only the relatively recent float glass processes which have produced good quality flat sheets of glass.

To answer the question we have to understand its thermodynamic and material properties.

Thermodynamics Of Glass

There is still much about the molecular physics and thermodynamics of glass that is not well understood, but scientist can give a general account of what is thought to be the case.

Many solids have a crystalline structure on microscopic scales. The molecules are arranged in a regular lattice. As the solid is heated the molecules vibrate about their position in the lattice until, at the melting point, the crystal breaks down and the molecules start to flow. There is a sharp distinction between the solid and the liquid state, that is separated by a first order phase transition, i.e. a discontinuous change in the properties of the material such as density. Freezing is marked by a release of heat known as the heat of fusion.


^^Molecular Arrangement in A Crystal

A liquid has viscosity, a measure of its resistance to flow. The viscosity of water at room temperature is about 0.01 poises. A thick oil might have a viscosity of about 1.0 poise. As a liquid is cooled its viscosity normally increases, but viscosity also has a tendency to prevent crystallisation. Usually when a liquid is cooled to below its melting point, crystals form and it solidifies; but sometimes it can become supercooled and remain liquid below its melting point because there are no nucleation sites to initiate the crystallisation. If the viscosity rises enough as it is cooled further, it may never crystallise. The viscosity rises rapidly and continuously, forming a thick syrup and eventually an amorphous solid. The molecules then have a disordered arrangement, but sufficient cohesion to maintain some rigidity. In this state it is often called an amorphous solid or glass


^^Molecular Arrangement In Glass

Some people claim that glass is actually a supercooled liquid because there is no first order phase transition as it cools. In fact, there is a second order transition between the supercooled liquid state and the glass state, so a distinction can still be drawn. The transition is not as dramatic as the phase change that takes you from liquid to crystalline solids. There is no discontinuous change of density and no latent heat of fusion. The transition can be detected as a marked change in the thermal expansivity and heat capacity of the material.

The temperature at which the glass transition takes place can vary according to how slowly the material cools. If it cools slowly it has longer to relax, the transition occurs at a lower temperature and the glass formed is more dense. If it cools very slowly it will crystallise, so there is a minimum limit to the glass transition temperature.


^^Density As A Function of Temperature In The Phases of "Glassy" Materials

A liquid to crystal transition is a thermodynamic one; i.e. the crystal is energetically more favourable than the liquid when below the melting point. The glass transition is purely kinetic: i.e. the disordered "Glassy" state does not have enough kinetic energy to overcome the potential energy barriers required for movement of the molecules past one another. The molecules of the glass take on a fixed but disordered arrangement. Glasses and supercooled liquids are both metastable phases rather than true thermodynamic phases like crystalline solids. In principle, a glass could undergo a spontaneous transition to a crystalline solid at any time. Sometimes old glass devitrifies in this way if it has impurities.

The situation at the level of molecular physics can be summarised by saying that there are three main types of molecular arrangement:

crystalline solids: molecules are ordered in a regular lattice
fluids: molecules are disordered and are not rigidly bound.
glasses: molecules are disordered but are rigidly bound.
[Just to illustrate that no such classification could ever be complete, recently scientists have succeeded in making quasi-crystals that are quasi-periodic. They do not fit into the above scheme and are sometimes described as being halfway between crystals and glass.]

It would be convenient if we could conclude that glassy materials changed from being a supercooled liquid to an amorphous solid at the glass transition, but this is very difficult to justify. Polymerised materials such as rubber show a clear glass transition at low temperatures but are normally considered to be solid in both the glass and rubber conditions.

It is sometimes said that glass is therefore neither a liquid nor a solid. It has a distinctly different structure with properties of both liquids and solids. Not everyone agrees with this terminology.

While there is no way you can put your hand in glass like you can into water glass is Supercooled.

So what do you think glass is?

roflmao

was this hardcore ripped, or do you just have no life

I think my brain just exploded.

^^Without Glass we couldnt live, No windows, no computer screen and much much more



^^ Not really, Some of it was from my grade 9 science class, and the diagrams and some information was the information i gave to teacher for the leason xD



^^Rofl, I am still looking for opinions or someones corrections.

No offence, but I really don't think anyone is going to spend their time reading all of that


I could be wrong though

Oh ----, sorry, didn't see it was in Homework and help, thought you were posting for the sake of it, lmao.

What exactly do you want answering? I'd give a go at helping you but from the post, it doesn't seem at all clear what the actual question is.

"What do you think glass is?" is a but vague IMO.

Without glass, society would still advance, we would just find another substitute for it.

^^ Well i know in grade 10 advanced science I need to make a poll of if people think glass is a solid or liquid, plus its just interesting to see what people think, But what is there to replace glass -.-?

http://math.ucr.edu/home/baez/physics/Gene...lass/glass.html :\

also its a solid that was a liquid

^^^lol it was a liquid and still is, because it is supercooled.

Substitute for glass? Plastic?

Glass is an amorphous solid. It has the properties of a supercooled liquid but is generally classified as a solid at room temperature.

By the way, the common misconception that old windows are thicker at the bottom because glass slowly flows over the centuries has been proved false. In the early 20th century window glass was produced by being poured onto a cooling table and let cool, then cut into sheets. The glass would be thicker at the location of the pour, which would be in the center of the large sheet which was then cut into smaller window sized pieces.

Some other points to prove that idea wrong:

-Some glassblowers produced glass by spinning molten glass to create a round, mostly flat and even plate. However, centrifugal forces resulting from the spinning would make the outside edge of the circular plate thicker. When the plate was cut into pieces and installed in a window the thicker side was placed down for stability and supposedly visual sparkle. However, some pieces have been found thin side down as a result of carelessness.

-If glass flows at such a rate that the naked eye can observe differences in thickness after a few centuries then the changes that should result in huge optical telescope mirrors should be observable by interferometry in a matter of days. Interferometry is insanely complicated but basically is used in telescopes and if the mirrors flowed at all it would cause problems.



Edit: Forget basically my entire post. I just noticed you said just about everything that I did so it looks like I just parroted you.

Molten glass: liquid
Glass: solid -.-

But i thought glass came from sand. all you needed to do was super heat it. at least thats what bill nye the science guy and tv said to me.

no life =D i say solid. heard of this be4 =)

That's why they call molten glass "Molten", cuz it's just liquid glass. Would we call rocks liquid, because at one point, they too were liquid?

Just something to think about. Bash away.

Glass is fire and sand.
Where is my prize?

Plastic is all i can say.

And i hope you didnt write that whole post yourself

I saw glass exists. What else do you need to know? It's there, we use it.


Not completely true.
We have plastics, and, also, primitive humans survived well enough without it.

*Sigh*, didn't you read?


I already knew glass did this, but I still find it interesting.

did you have a brain fart....

Glass is definitely a liquid IMO - an extremely viscous one. You can tell by looking at old windows because they are fat at the bottom and thin at the top.

I'd hope that after a year this homework assignment may have been handed in.

Closed.