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Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

ceramics.org

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Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#61

Post by nemo44x »

smnrchrds wrote: post #58
flatline wrote: post #55

Earlier quoted context omitted.

I mean, the HS teacher that told me this had a masters in Mech E. Or so he claimed, hmm...

He must not have been the top of his class if he had ended up a HS teacher. Which is actually kinda sad. Pay and working conditions for teachers shouldn't be so that being a teacher is regarded as a failure.

Is it regarded as a failure? Teachers in public schools work part time for 25 years and get a scaling pension they “negotiated” with the politicians their union dues elected. I’d call them fantastic winners. Grifters? Sure. But certainly not losers.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#62

Post by ThenAsNow »

pfdietz wrote: post #35
parsecs wrote: post #19

Earlier quoted context omitted.

Or how reentry heating is apparently caused mostly by friction. (Compression of air is the main cause in actuality)

No, actually friction is closer to the truth. It's air running into air at a shock, a process that generates entropy, just as friction does. Compression is a process that is adiabatic, generating no entropy. And in an ideal gas the density increase across a shock reaches a finite limit even as the mach number goes to infinity.

I can't make sense of your claim. Compression could be done adiabatically, or not, but that doesn't mean it's isothermal or somehow inherently adiabatic. In fact, for it to be isothermal would require the transport away of compression heat, which would be decidedly non-adiabatic.

The parent is correct.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#63

Post by ivalm »

smnrchrds wrote: post #58
flatline wrote: post #55

Earlier quoted context omitted.

I mean, the HS teacher that told me this had a masters in Mech E. Or so he claimed, hmm...

He must not have been the top of his class if he had ended up a HS teacher. Which is actually kinda sad. Pay and working conditions for teachers shouldn't be so that being a teacher is regarded as a failure.

You are the one regarding them as failures. I had a variety of teachers in school, some were very educated (PhDs), and simply found a calling in teaching. Not everything is about money, you shouldn’t look down on teachers.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#64

Post by ordu »

nemo44x wrote: post #45
torben-friis wrote: post #3

Earlier quoted context omitted.

What other unsubstantiated claims did she make?

Almost everything we think (including me) is probably trash. We just need to accept we are mostly idiotic. Unless we put the time in to understand something that _maybe_ is somewhat understood by people that have put their lives into it. Truth is (heh) we are all mainly full of shit. We think we know more than we do. We confuse truth for BS constantly. We spend countless breaths debating unfalsifiable opinions as if…

> Almost everything we think (including me) is probably trash. We just need to accept we are mostly idiotic.

I do not like this attitude. Everything is false, because the truth exists only in ideal condition of math. But it doesn't mean that we are all idiotic and know nothing worthy knowing. The trick is to understand the relation between knowledge and the reality, to feel this relation in your guts. It helps to know a lot of falsehoods, and to be smart, even wise and knowledgeable.

> We are all mainly dumb at most things.

I could agree with this, because to really know something one needs to spent all his life researching the topic. And even the life full of the dedicated research might be not enough.

But as I see, to be dumb is not so about having no knowledge, as about having no idea of limits of one's knowledge.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#65

Post by ThenAsNow »

bernulli wrote: post #44
pfdietz wrote: post #35

Earlier quoted context omitted.

No, actually friction is closer to the truth. It's air running into air at a shock, a process that generates entropy, just as friction does. Compression is a process that is adiabatic, generating no entropy. And in an ideal gas the density increase across a shock reaches a finite limit even as the mach number goes to infinity.

I am having trouble seeing how compression in a shock would be isentropic? Care to elaborate? And why passing through a shock (compression) is akin to friction, but not to compression?

Compression due to a shock is not isentropic. Parent is incorrect. This is basic gasdynamics. An accessible reference: Modern Compressible flow, by Anderson.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#66

Post by dragonwriter »

nemo44x wrote: post #61
smnrchrds wrote: post #58

Earlier quoted context omitted.

He must not have been the top of his class if he had ended up a HS teacher. Which is actually kinda sad. Pay and working conditions for teachers shouldn't be so that being a teacher is regarded as a failure.

Is it regarded as a failure? Teachers in public schools work part time for 25 years and get a scaling pension they “negotiated” with the politicians their union dues elected. I’d call them fantastic winners. Grifters? Sure. But certainly not losers.

> Teachers in public schools work part time

Typically full-time and usually year round, though some work seasonally for about 3/4 year (but still full-time), with commensurately reduced annual pay.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#67

Post by bernulli »

pfdietz wrote: post #53
bernulli wrote: post #44

Earlier quoted context omitted.

I am having trouble seeing how compression in a shock would be isentropic? Care to elaborate? And why passing through a shock (compression) is akin to friction, but not to compression?

Because compression, as normally considered, does not generate entropy. It causes gas to become hotter because the temperature has to be higher for entropy to remain constant, as the volume is reduced. This is a reversible process. But shocks are inherently irreversible. But as my last sentence said, as the mach number goes to infinity the density increase across the shock is finite. Therefore, compression cannot be…

I have never seen compression to be considered inherently reversible, certainly not in the aerospace or hypersonics/reentry communities. I assume you come from a different background?

Care to explain your second argument? Even when the density reaches a limit, the change in pressure over the shock does not, so you can pump in energy arbitrarily (of course your gas would dissociate at some point). The total pressure loss can be complete if your initial Mach number is high enough.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#68

Post by GuB-42 »

nikisweeting wrote: post #2

Finally! I always knew my 7th grade science teacher was full of shit on that one, she was so adamant about some things that turned out to be wrong. This one was maybe more excusable because it was common to teach at the time. Maybe it ended up making us better students in the end because we learned to fact-check our teachers, and not to be adamant about things we only think are true (though I'm still guilty of that m…

That's the reason why I love the internet. Things are so easy to fact check now, at least compared to the way it was before.

Many people talk about the problem of "fake news". What they may not realize is that falsehood have always existed, but we now have unprecedented tools to debunk them.

When I was a kid, I learned loads and loads of bullshit, the glass thing was one of it. The problem was, how could I know it was wrong? Obviously, I didn't know enough about material science to figure it out by myself, and I didn't know any material scientist. Books were mostly useless for that purpose, searching for the answers would have taken days at best, and I didn't have that much time to debunk something that insignificant. Now just searching "glass thicker at the bottom" on the web yields exactly what I need.

In fact, I am quite sure, there is much less bullshit going on today, but it looks like there is more because that these are so much easier to figure out.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#69

Post by nemo44x »

ordu wrote: post #64
nemo44x wrote: post #45

Earlier quoted context omitted.

Almost everything we think (including me) is probably trash. We just need to accept we are mostly idiotic. Unless we put the time in to understand something that _maybe_ is somewhat understood by people that have put their lives into it. Truth is (heh) we are all mainly full of shit. We think we know more than we do. We confuse truth for BS constantly. We spend countless breaths debating unfalsifiable opinions as if…

> Almost everything we think (including me) is probably trash. We just need to accept we are mostly idiotic. I do not like this attitude. Everything is false, because the truth exists only in ideal condition of math. But it doesn't mean that we are all idiotic and know nothing worthy knowing. The trick is to understand the relation between knowledge and the reality, to feel this relation in your guts. It helps to kno…

No - truth doesn’t only exist in an ideal condition of math. I mean, yes maybe literally in some ways, maybe. But not really. Math doesn’t prove the sky is blue on a sunny day.

My main point is that of falsifiability. You don’t need math to make a falsifiable argument. However, much of our discourse can’t even meet this basic qualification.

Re: Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

#70

Post by aoki »

ars wrote: post #56
nikisweeting wrote: post #2

Finally! I always knew my 7th grade science teacher was full of shit on that one, she was so adamant about some things that turned out to be wrong. This one was maybe more excusable because it was common to teach at the time. Maybe it ended up making us better students in the end because we learned to fact-check our teachers, and not to be adamant about things we only think are true (though I'm still guilty of that m…

The article says the glass does actually have a viscosity, so maybe she was not quite that wrong - just about the magnitude. I think glass has a viscosity, but other solids do not, but will creep. I hope my understanding is correct - if not, can anyone help explain?

I believe you are correct. I had to shorten the title, and removed “observable” because the word “medieval” already refers to the science class meme that the viscous flow is at human history timescale (as opposed to ~1 nm/10^7 years).
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