Science question : Does the viscosity......

OK, checked out a few links and it would seem that, at best, scientists are in dispute over whether glass is really a liquid or a solid.

The disputes would seem to be semantic ones over what exactly constitutes a liquid or a solid. Glass however is structurally, fundamentally different to other solids.

Also, it would seem that the "ancient window panes are thicker at the bottom" thing has never been subjected to any rigourous analysis and may just be due to ancient glass making methods.

In everyday terms glass is clearly a solid. It has no everyday observable liquid properties but I guess the debate has persisted because it's a nice one to throw into the pub conversation

Michael.

 

A thread about interesting water facts, now that makes a change :bookworm: . We still don't know the reason for Voodoo's interest though do we? Come on Voodoo, spill the beans!

 

No reason in particular . I think of stuff like that all the time but this time it wasn't toooooooo nerdy to ask :shame: .

Another good one was; "Why do all drinks, such as coke, foam up when you pour them but carbonated water does not ?"

I came to conclusion that it was down to the viscosity of the water (no sugar etc) and surface tension.

Anyone else care to add to that one :MILD: ?

Oh, and cheers for the interesting reponses.

 

Voodoo, you might like this page:

http://www.guardian.co.uk/notesandqueries/

...people ask questions like yours and other people write in with answers. Started in The Guardian a few years ago

Michael.

 

Might it not just be that drinks like coke have far more disolved CO2 than carbonated water?

 

Cheers Michael .

I remember that the Daily Mail used to have a similar type of section.
Only decent bit of that paper worth reading !

:duck:

 

Just spotted this thread and puts on chemist's hat.

Glass actually ocupies a half-way house between solid and liquid. Strictly, a solid is any material with a fixed structure, with the atoms held in a lattice in a fixed relationship. A liquid is a material where the atoms or molecules are not fixed in a rigid lattice, have mobility and can slide past each other (what we call flow). The third state of matter is gas, where the atoms or molecules have complete freedom. (There is a fourth state of matter, plasma, where the atoms are stripped of their electrons).

But back to glass. It doesn't have the rigid crystal lattice of a classical solid, but neither do its atoms have the freedom characteristic of a classical liquid. Its structure is actually amorphous. As a result, it does have some flow properties, and I believe it to be true that, over time, windows will increase slightly in thickness at the bottom. Glass has a relatively short lifetime in the geological scale of things - obsidian, the black natural glass associated with volcanism, has a lifetime of only a few tens of thousands of years. Meaning that I probably won't be around to see its demise.

 

Dihydrogen monoxide is actually one of the most bizarre substances in the universe. It simply doesn't behave how it should. Consider its relative in the Periodic Table, hydrogen sulphide, "rotten egg gas" - it's a gas, even though sulphur has a higher atomic weight than oxygen.

Much of the secret lies in the molecule itself. It's extremely polar, which means that it tends to like its own company. It goes in for hydrogen bonding in a big way. Now, while hydrogen bonding is nowhere near as strong as covalent bonding (which holds molecules together), it still exerts a force that is far from negligible. That hydrogen bonding makes water a liquid when all the rules suggest it should be a gas. The hydrogen bonding seems to like groups of six, which reflects (sort of) on the six-fold symmetry frequently noted in the frost patterns on windows.

Water also has the highest latent heat of fusion and latent heat of evaporation of any known liquid, that is, the energy needed to change the state of the stuff, from ice at 0°C to liquid water at 0°C, and from liquid water at 100°C to steam at 100°C is very high. In other words, it's not that easy to turn water into ice at one end or steam at the other, so it remains a liquid over a considerable range of temperatures.

The bizarre behaviour is fundamental to the existence of life as we know it. Because the maximum density is reached at a temperature above freezing point, it means that ponds freeze from the surface downwards, not from the bottom up, making life in water possible all year round, even in the coldest places. The polarity also makes it a very good solvent for all sorts of natural things and the perfect transport medium for materials in cells.

So, next time you quaff a glass of the stuff, think how magnificent it is and say thank you to it, because without it, you wouldn't be here and neither would your hi-fi.

P.S. So firmly stuck in gasbag mode that I forgot to aswer the question, why does water expand on freezing? It's that hydrogen bonding again, plus the fact that the molecule is a particular shape, with its hydrogen-oxygen bonds sticking out behind it, making an angle of 104.5 degrees with each other under normal circumstances. When water reaches 4°C, the molecules have been pushed as close to one another as they will be. Below 4°C, the water molecules begin to align themselves into the crystal structure of ice. This requires the water molecules to widen the angle between the oxygen- hydrogen bonds from the usual 104.5 degrees. When this happens the water molecules take up more space, hence expansion.

 

You must be thinking of the triple point. This is the combination of temperature and pressure at which a substance can exist as a solid, a liquid and a gas. For water this occurs at 0.01 deg C and 6.104 mbar. Below that pressure, water won't enter the liquid state at all but will sublimate from solid to gas. Interestingly the pressure and temperature on Mars is such that water does sublimate in just this way. I don't think the triple point is unique to water though.

 

Excellent posts there Tones, very informative. It's good to know we have you to count on with such questions .

 

What about my post

Mine was informative too :cry:

 

And a big thankyou to Techo. for his wise words too

(I hadn't read your post before...)

 

Guy's.........I am astounded .

And I'd like to thank you all for keeping this conversation informative - yet amusing .

All in the name of Zerogain.

 

P.S. The viscosity of water (how it all started). The viscosity of all liquids decreases with increasing temperature, the question is by how much. Here's the good oil from the Chemical Rubber Handbook, one of the Bibles of the chemistry profession, which tabulates the viscosities for water. They range from 1.787 centipoise for water at 0°C to 0.2818 centipoise for water at 100°C, or, in layman's terms, from very fluid to even more fluid.

 

You seem to have not read what I said correctly old chap

 

Sorry MO! :shame:

Michael.

 

First day of Chem Eng, guess how many knew what that was Most amusing.

 

I suspect that they simply put in more gas under more pressure. The higher the pressure, the more gas will dissolve. I doubt that the sugar has anything to do with it and surface tension considerations wouldn't play any part because there isn't that much surface.

All divers are of course familiar with the fact that more gas dissolves under pressure. Come up too quickly from deep enough (and it doesn't have to be that deep) and the nitrogen that dissolved in your blood comes out in bubbles - the result is the excruciatingly painful condition called "the bends", which was fatal before they realised what caused it and introduced decompression chambers.

 

And if it wasn't for that fact all the ice would be at the bottom.

Bob