(classical music)
(chalk writing)
- Hi there.
I'm Lauren.
This is Brain Stuff
and here's our question for the day.
Is glass a liquid or a solid?
Now, if you've ever looked
at the window panes in an old building,
you might've noticed
that the glass was ripply
and sort of thicker towards the bottom
and you might have lept gazelle-like
to the logical sounding conclusion
that the glass had flowed
into that shape very slowly
over a period of centuries.
You might've even read
about that in a textbook.
The truth is though that that
glass was always that way.
Okay, so up through the 1800's,
panes of glass were made by hand.
Glass blowers used what's
called the crown process.
In the crown process,
they'd take a bubble of very hot glass
and rotate it fast
so that the centrifugal
force would spin it out
into a large, mostly flat disc.
The disc would be thicker at the edges
and each pane cut from it
was bound to be a little bit lumpy.
Workers tended to install these
with the thicker side down
probably because the slightly larger edge
provided slightly better balance.
So the glass in those
old panes isn't flowing,
at least not that researchers can discern.
They've looked at samples
from over 2,000 years ago
and haven't found tell
tale evidence of flow.
Now, scientifically speaking,
glass is considered an amorphous solid.
That means its' atoms and molecules
are locked into place like a solid
but those molecules
are arranged more
randomly than most solids,
more similar to a liquid.
If you want to get into semantics,
you could sort of call
glass a supercooled liquid.
That's a liquid that's been cooled
to below its melting point carefully
so that it doesn't crystallize
and that's part of making glass
but at that stage,
it's still hundreds of degrees
above room temperature.
It's then cooled until it transitions
into the rigid amorphous solid
that we all know and love.
So you might say that glass
is its own state of matter,
neither a liquid nor a solid.
That should just about
wrap up this question.
If you have any other questions
that you'd like us to answer,
then leave a comment somewhere down there.
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