|We are studying states of matter. We have a
question about glass. We have discrepant
information from the Internet about whether, at
room temperature, it is a liquid with a very high
viscosity or a solid. Could you please answer
our question: At room temperature, is glass a
solid or a liquid? Thank you very much!
|Question Date: 2003-12-10|
Actually, I believe that both answers are
correct. I think the real question is, "What is
Liquids, solids, and gases are all made up of
atoms. Now you may have learned that in a liquid,
the atoms are all jumbled and tumbled together.
Most solids, on the other hand, are
crystalline, which means that the atoms are
neatly arranged. Think of billiard balls all
stacked tightly together, or maybe the ball and
stick models you may have seen in class.
Now, a glass is somewhere in between. The best
way to think about a glass is to imagine the
liquid and imagine that you can actually see all
of the atoms moving around. Now take a picture.
When you look at the picture, the atoms are frozen
in time and place. This is a glass.
Think of what happens when you freeze a glass
of water. At first, the atoms in the water are
moving around because the water is warm and they
have a lot of energy. As the water cools, the
atoms move more slowly. As they lose energy, the
tend to arrange themselves in the best possible
manner and form ice crystals. However, this takes
time. If you cooled the water so quickly that
the atoms couldn't move to the best locations, you
would have a glass.
This is what it means to say that a glass is
a liquid with a very high viscosity. The atoms
would like to move to a position that has a lower
energy, but they're stuck or frozen in place
I once read a definition that said if you were
to kick a piece of material with you barefoot, and
it hurts, then it's solid. That might be a silly
definition, but it's pretty good. The windows in
your school are glasses. They're solid, too.
Hope this helped.
You are asking a question which is really at
the edge of our current knowledge of physics. In
fact, there is an entire sub-field of physics
designed to answer exactly this question. So, the
short answer to your question is that, according
to a glass expert down the hall from me, nobody
In many solids, the atoms of the material
arrange in a regular pattern called a crystal.
In these materials, there is a sharp transition
between the liquid and the solid, and quite a bit
is known about this transition. In a glass,
something much weirder happens. As you cool the
liquid down, the molecules slow down and start
hitting each other more and more. As this happens,
they begin to get stuck on each other, until
eventually, they are so stuck that they are unable
to flow. This is called "jamming". What
seems to happen is that the time it takes for a
glass to flow gets higher and higher, until
eventually it takes thousands, or hundreds of
thousands, or billions of years. So, does glass
flow? Yes. Is it a liquid or a
solid? It depends on how long you look at
it. I would probably tell you that it was
neither - it's just a glass.
Just to show you how weird glasses can be and
to give you an example of what I mean, there are
materials (such as pitch tar) that can be poured
into a funnel. Every 80 years or so, one drop will
fall from the bottom of a funnel. If you smash it
with a hammer, however, it will shatter.
So over an 80 year period, it is a liquid.
Over the time it takes to smash it with a hammer,
it is a solid.
The last thing I want to say is that I've heard
that stained glass windows in old churches look as
if they have flowed. Apparently, there is still a
big argument about whether that glass has flowed
over a few hundred years or if the glass looks
that way because of how it was made.
This is a good question. The difference
between a crystal and a liquid is that a crystal
has a long range periodic structure that goes on
forever . That is, once the unit cell is
determined, one simply repeats this UNIT CELL
A liquid on the other hand is a DISORDERED
material ... It has only a very short range
structure ; beyond a few atom diameters liquids
are significantly disordered---they possess no
long range structure.
Now, a GLASS is frozen liquid... so
while a glass has the thermal properties (like the
specific heat) of a crystal , it shares the
disorganization at long range with a liquid.
So a glass is a solid ; but it can also be
described as a frozen liquid (of very high
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