It's a theory limit experiment.
Newtonian physics; Every Action Has an Equal and Opposite Reaction; An object at rest will remain at rest... and all that. Explained almost everything we encountered in the universe for the best part of four hundred years; and it still works pretty well on earth (and other places) provided you aren't getting into sub atomic particles or looking at stuff traveling long distances, like accross galexies; when Einstein's theories start to explain the anomolies where Newton's doesn't quite work.
Fluid Dynamics. Its not my strong suit. I have to admit, I think I'm a bit of a rationalist... during my Pysics A-level, when it was explained that the abscence of an electron, or a 'hole' could be a charge carrier, carrying an 'abscence of a charge, I did ponder whether we might then employ this principle, and re-tune the particle accelerator from the back of an old TV set to fire 'holes' rather than electrons, and hence create an 'anti-matter-ray-gun' to de-materialise the college parking warden... but 'imaginary numbers'? The square root of minus one, is it?!?!?!?!? Nope... one step TOO surreal for me.
So... Fluid Dynamics when I got to University, where they had one of the few Super-Sonic wind-tunnels in civilian hands in the country..... imagine a perspex pipe about two foot in diameter, and no fan. Aparently to get air to shift that fast, it was provided by compressed air tanks, bit like the ones in Machine Mart... here you go....
That sort of thing, usually hidden in the corner of mechanics workshops for them to run thier paint spraking kit or Formula 1 style wheel-nut removal guns off..... but a LOT bigger. Aparently the reciever tanks for the wind tunnel were under one of the college car-parks and were modified Petrol Station fuel tanks! And were pumped up, by a couple of large 'plant' compressors, the sort of things you see in road-works, on the end of the hose Paddy has his jack-hammer to knock another hole through the tarmac... only a lot bigger.... and it took about a week to charge them up, to run the tunnel for about half an hour or something..... but I detract.
The Co-Efficient of Drag... how slipery your new Audi is. cD. This is one of the many 'Dimensionless Units' of Fluid Dynamics... and where I sort of lost the plot with the topic... because the subject is full of them..... and I call them 'Fudge Factors'!
Thier sums don't work you see, so they don't use them. Instead they create unresolvable equations, and then eliminate ALL the variables by taking two unresolvable equations, and make a ratio from them!
So the Co-Efficient of Drag, is simply a ratio of how much more easily fluid flows around your Audi, than it does a brick of the same length and frontal area.
And this is all well and good, and 'seems' to work reasonably... as long as you are comparing, say a brick in a hurricane with a car going up the motorway.
But when speeds get much over a strong wind, the comparisons start to break down.....
Its the 'Flat Earth' Principle...... From perspective of standing in a field.... looks pretty flat. Not until a REALLY good engineer comes along, and bored a ten mile long hole through a hill, perfectly flat, straight and true to within 3" over its entire length... then fills it with water, and the poor fella 'legging' the barge through the tunnel gets stuck half way when the cabin scrapes on the roof... you stop to ponder how water can 'curve' in the trough at the bottom.... and be deeper in the middle than at the ends!
Or what fluid dynamisists call 'Boundry Effects'.. they like these... its there forte.
You have water flowing down a pipe, they can predict and tell you everything and anything about whats going on in the middle of the fluid... but where it is close to the pipe itself..... stuff goes a bit fuzzy... and thats what they like looking at.
So. Oil flowing around a car engine. This is all pretty hum-drum stuff. Oil is a low to medium viscocity fluid, pretty much does everything they expect it too.
Water, in the sewage system..... again, hum-drum stuff, does pretty much what they expect it to... until it freezes.....
Sugar in a refinary? Bit more challenging....
BUT, and where this experiment has more relevence; PLASTICS.
A lot of materials we consider to be solids, aren't. And the best one is GLASS.
Glass, is actually a super-cooled fluid. When hot, it flows as a liquid, then as it cools it 'sets'... no actually it doesn't.
Water. heat it up it boils. And if you did the experiment at school, it boils at 100 Degrees C. Up to 100C you add heat, that heat makes the thermometer in the beaker go up... when it boils you have to keep adding heat, but the temperature STAYS at 100 C until its all boiled. There is an energy associated with teh change of state. Works the other way around too, when water freezes. Take heat out of water, thermomenter falls, until you get to 0C when it turns to ice, and you have to keep taking heat out until its all frozen before you can get the temperature to drop ant more.
Same happens when you melt metals; they have a melting point, and they 'change state' from solid to liquid.
GLASS DOESN'T... glass is a liquid.
Sweeping up the shards of one I dropped out the dishwasher yesterday might suggest to the contrary... but TECHNICALLY Glass IS a liquid.
Get Glass molten, and start cooling it; like engine oil, when hot it goes thin and runny, but as it cools it's viscocity increases, and it gets thicker and thicker... until it goes 'Plastic'... which means 'mouldable'... and where glass-blowers do thier stuff with it. Then as it cools further, it 'sets' right?
Well, sort of. It goes SO thick, that it SEEMS solid, but there is no 'latent heat' phase where it changes state; it just cools and cools and cools some more, and gets thicker and more and more viscouse until it is 'effectively', but not actually solid.
This is important, because as mateials science has evolved they have found more and more of these 'super-cooled' fluids... and an awful lot of them are around you now.... modern 'Plastics'... and thier 'melting point' or where they 'set' is actually known as 'The Glass Transition Point' because they dont change molecular structure like metals chyrystalising when they 'set'.
Now, GLASS FLOWS.
Turning stately homes into tourist attractions, and attempting to renovate them within increasingly stringent 'listed building' regulations..... making new window frames, they found that Georgian Window Glass seemed to be thicker at the bottom than the top...... Not a lot... but a bit. 1/4" glass.... measured up 4mm at the top, 7mm at the bottom or there-abouts.
Logic says, cast 'flat' in a tray, when made it was uniform thickness. SO logically, the explanation is that 200 years sat vertically in a frame... its 'flowed' to the bottom... like a candle left in a sunny window.
But since No-One made scientific measurements of the stuff, 200 years ago, AND the manufacturing process wasn't brilliantly controlled... the suggestion remains a 'Theory'... one that is outside the scale of human experience....
So this kind of experiment; looking at how super-viscouse fluids behave over long time-scales, into the boundaries of human experience and in the margins of the known and predictable....
And a very valid scientific study.
1/ Its cheap!
You need a funnel, some old tar, and a beaker.... and some-where to put it. And some-one to note the level of tar in the funel every morning.
You dont need to make a thirty foot mirror, and launch it into space, or anything!
2/ Its Relevent Science
It takes a hard to prove Theory, and adds evidence to support or deny it.
3/ Its USEFUL!
OK... how long it will take the top of a road to flow into the drains might not be that helpful.... though given Council works Dept round here, I wouldn't be too keen to place a bet that the surface will be remade by them before it does!.... But transfering the data to other super-viscouse or super-cooled fluids, and particularly 'engineering plastics'... has a LOT of practical relevence.
We have only been using plastics for about 100 years, and an awful lot of modern plastics have only been ion common use for perhaps thirty or forty. We STILL don't know 'all' about them. Particularly in terms of their degradation and long term stability.
Well somebody was going to do it sooner or later !
