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The Pitch Drop Experiment

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cr1t
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« on: April 09, 2013, 14:16:08 PM »

http://smp.uq.edu.au/content/pitch-drop-experiment

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BoogieMonster
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« Reply #1 on: April 09, 2013, 14:48:55 PM »

That's a "cool" experiment, reminds me of a common misconception: Glass does not flow over the centuries, it behaves like a solid.

I can't count the number of times I've had to point this out to the chagrin of bystanders at parties. (Aside: I'm not always that popular at parties.)

I usually try to mitigate shooting down their cool "long time" fact by providing my own: There's a project to build a 10,000 year clock.



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brianvds
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« Reply #2 on: April 09, 2013, 15:53:10 PM »

That's a "cool" experiment, reminds me of a common misconception: Glass does not flow over the centuries, it behaves like a solid.

I can't count the number of times I've had to point this out to the chagrin of bystanders at parties. (Aside: I'm not always that popular at parties.)

I seem to remember having seen, at a flea market, old bottles from garbage dumps that were deformed in all manner of ways, as if the steady pressure from garbage above them had slowly deformed them. Perhaps heat in the dump slightly melted them?

Also, in some ares one can see sedimentary rocks that were presumably originally straight layers, deformed into wavy forms without much in the way of cracking. Rock consists pretty much of the same stuff as glass.

So if glass cannot flow, I have to wonder how I explain the above two observations?

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BoogieMonster
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« Reply #3 on: April 09, 2013, 17:14:04 PM »

I seem to remember having seen, at a flea market, old bottles from garbage dumps that were deformed in all manner of ways, as if the steady pressure from garbage above them had slowly deformed them. Perhaps heat in the dump slightly melted them?


Or perhaps heat from the seller's blowtorch...

Quote
Also, in some ares one can see sedimentary rocks that were presumably originally straight layers, deformed into wavy forms without much in the way of cracking. Rock consists pretty much of the same stuff as glass.


I have no frikkin clue, but solids can bend. Moreover I wonder if it couldn't be formed by a process similar to bimetals, where layers of different material expand and contract to different degrees in response to the same amount of heat, producing a bend.
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Mefiante
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« Reply #4 on: April 09, 2013, 19:37:32 PM »

I have no frikkin clue, but solids can bend. Moreover I wonder if it couldn't be formed by a process similar to bimetals, where layers of different material expand and contract to different degrees in response to the same amount of heat, producing a bend.
Rocks usually deform in response to stresses from a variety of tectonic forces.  Folded and warped strata often show signs of cracking but the cracks were filled by subsequent geological activity.  In other cases, metamorphic processes (heat, pressure) change the rock’s properties, including its mechanical ones, and these rocks can behave visco-plastically and deform without cracking if the deformation is sufficiently gradual.



As to the question of what the material phase nature of glass is, the situation is, as ever, hardly as black-and-white as we’d like it to be.
Conclusion

There is no clear answer to the question “Is glass solid or liquid?”.  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.  In terms of its material properties we can do little better.  There is no clear definition of the distinction between solids and highly viscous liquids.  All such phases or states of matter are idealisations of real material properties.  Nevertheless, from a more common sense point of view, glass should be considered a solid since it is rigid according to everyday experience.

'Luthon64
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Rigil Kent
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« Reply #5 on: April 10, 2013, 07:41:39 AM »

visco-plastically
Mmmm....



Surprisingly, the handsome Rigil attended the party after all, and on arrival the flustered hostess tentatively and visco-plastically draped herself around his broad shoulders in welcoming embrace.


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Mefiante
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« Reply #6 on: April 10, 2013, 08:02:50 AM »

… the flustered hostess … visco-plastically draped herself around his broad shoulders in welcoming embrace.
Kent must be a patient man to tolerate such creepy sliding behaviour by a springy non-linear dashpot. Wink

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Rigil Kent
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« Reply #7 on: April 10, 2013, 09:58:11 AM »

Kent must be a patient man
It was sheer stress, I kid you not. Cheesy
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