An Overview of Glass

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An Overview of Glass

Glass is a very odd substance, is it a solid or a liquid? There are

many reasons why it can be considered either of the two, but still

most people are unsure of its state. Glass may be a state of matter

that is neither solid nor liquid.

A liquid has viscosity, which is a measure of its resistance to flow.

So water may move very quickly because it has a high viscosity, but

oil has a high viscosity so it moves slower. If something were to have

a very high viscosity then it may seem like a solid but it would be an

amorphous solid. An amorphous solid is a liquid that looks like a

solid but doesn't have crystals so it just sits there for a long time

and slowly moves.

A solid has viscoplasticity, which is the resistance to flow under

plastic deformation. If you were to punch plastic with your hand it

would deform then go back to shape, but if you were to hit it with a

steel pipe there would be a dent in the plastic and it wouldn't go

back to its original form. So the viscoplasticity is like how much of

a force you have to put on it until there is a deformation. Some

materials don't flow but creep these materials are known as plasticity

materials. The only way they can be deformed is to be held under

stress (pressure) for a constant amount of time.

Since as far as we can tell both those things hold true for glass so

those aren't good ways to establish a for sure state of matter for

glass. Another way to decide where glass is a liquid or solid is to

say there is a minimum amount of shear stress required to permanently

deform it then it's a solid. There are materials which have some

limited flow known as viscoelasticity. The material will deform

elastically under stress. If the stress is held for a long time the

deformation becomes permanent even if the stress was small.

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