Wikipedia:Reference desk/Archives/Science/2014 March 8

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March 8

Prince Rupert's Drops

Is it possible to make a structure with qualities similar to Prince Rupert's Drops out of any material other than glass? 91.77.174.211 (talk) 09:46, 8 March 2014 (UTC)

• Since there are no answers yet, you might be able to do so with different types of glass than soda-lime glass which is mostly silicon dioxide. Sulfur forms a glass when quenched from a molten state, but it reverts to crystalline form over night if kept at room temperature. The fact sulfur glass is ductile at room temperatre and rather quickly recrystalizes would make it unsuitable at room temperature. I suspect doing the same experiment at a much lower temperature might prevent the reversion to crystal long enough for the formation of PRD's to occur. It would be a very interesting experiment. Hopefully some materials scientist will comment. μηδείς (talk) 20:06, 8 March 2014 (UTC)

I'm not sure, but perhaps molten obsidian might work too. Or perhaps some glasslike polymers, such as polycarbonate... 24.5.122.13 (talk) 21:11, 8 March 2014 (UTC)

Yes, it should. Obsidian still has about the same SiO2 content as normal soda-lime glass, ~75%. So it is basically normal glass for all intensive purposes. When I questioned my bro-in-law on this yesterday, he said basically any quickly-quenched enough non-ductile glass in the broad sense will work. What matters is the compressive mechanics mentioned in the article.μηδείς (talk) 21:13, 9 March 2014 (UTC)

How about non-intensive purposes? --ColinFine (talk) 17:39, 10 March 2014 (UTC)

That was for the benefit of User:JackofOz, whom I won't name here. μηδείς (talk) 17:15, 11 March 2014 (UTC)

I'm not even watching this page, so I haven't even seen your invitation to outrage (which I would politely decline). -- Jack of Oz ^{[pleasantries]} 21:31, 11 March 2014 (UTC)

S. C. Johnson & Son, Jack! You are the one who used the "all intensive purposes" phrase as a joke just this month, and my allusion to it was meant as an homage, not an outrage. μηδείς (talk) 03:38, 12 March 2014 (UTC)

Metal glasses might also work. See also Glass#Amorphous_metals, which specifically mentions rapid quenching. SemanticMantis (talk) 15:39, 10 March 2014 (UTC)

DARPA has been at work trying to make explosives by trapping energy in polymer chains of carbon monoxide. The technology for doing so is described in "Pressure-Induced Polymerization of Carbon Monoxide:  Disproportionation and Synthesis of an Energetic Lactonic Polymer" by a team of researchers at Lawrence Livermore National Laboratory (for those who don't know, this is one of the United States' two nuclear weapon design labs). [1]

What you get when you throw CO into a diamond anvil cell and/or a large volume press, then turn the pressure way up is a solid polymer that "is metastable at ambient conditions, spontaneously liberating CO2 gases exothermically". In layman's terminology, it blows up. This may actually be the most extreme application of trapping significant amounts of energy in a molecular structure to produce an explosive without recourse to redox or nuclear reactions - which is what the Prince_Rupert's_Drop does. loupgarous (talk) 01:20, 12 March 2014 (UTC)

Is there some special purpose for caring if the reaction is not oxidative? μηδείς (talk) 03:40, 12 March 2014 (UTC)

Quoting the original poster's question, "Is it possible to make a structure with qualities similar to Prince Rupert's Drops out of any material other than glass? "

Since the detonation one gets from touching the narrow end of a Prince Rupert's Drop is not oxidative in nature, that's why. I was being maximally responsive to the question.

The Prince Rupert's Drop phenomenon is the most well-known case in which thermal stress can be captured in the structure of an object to be released all at once as destruction of the object (but only after a specific force is placed at a key part of the structure) later.

Granted that Livermore/DARPA's CO polymer doesn't require that specific a stimulus to detonate, and that the detonation by-product species include CO2 seems to imply that after the initial detonation, combustion of the CO with ambient oxygen occurs and may contribute energy to the total energy output of the detonation, my answer still is a responsive answer to the OP's question. loupgarous (talk) 04:26, 12 March 2014 (UTC)

Name of the juncture between the leg and the pelvis

Hi guys. I'd like to know if there's a particular name for the part of the body where the leg and the pelvis connect, analogous to the armpit where the shoulder and the arm connect. Me searching Wikipedia has come up empty, and I'm inclined to believe that the closest of an answer I can get is the perineum, but I don't know it it's correct. Any other ideas? :) --Sky Harbor ^(talk) 13:28, 8 March 2014 (UTC)

That would be the hip joint. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:15, 8 March 2014 (UTC)

As Baseball Bugs already told you, you're probably talking about the Hip Joint. Perhaps less likely, you're thinking about the groin? — Preceding unsigned comment added by Krikkert7 (talk • contribs) 16:54, 8 March 2014 (UTC)

"Groin (n) - The crease or hollow at the junction of the inner part of each thigh with the trunk." [2]

What does the letters Mw stand for?

I mean on the letters Mw that symbolize molar mass. May it stand for Molar Weight? 5.28.157.185 (talk) 14:54, 8 March 2014 (UTC)

Specifically, "Mw" is Weight Averaged Molecular Weight, in contrast "Mn" would be Number Average Molecular Weight, see also Molar mass distribution. The difference between the two reflects the polydispersity of the molecule, something you could read about in our article on polydispersity were it not muddled by IUPAC revisionism. Also, when it's written as "MW" or "FW" it's usually intended as a general abbreviation for "Molecular Weight", "Molar Mass", and/or "Formula Weight". (+)H₃N-Protein\Chemist-CO₂(-) 15:03, 8 March 2014 (UTC)

Mining, rails and wheels made of steel and/or iron.

The rails on a railway and the wheels of a train-wagon are obviously made of top-quality steel, so that it can withstand the pressure, the speed and the weight and not be worn down so easily.

My questions are; would mining-wagons (in the past especially) be made of steel as well or would it be made of iron? Perhaps the wagon itself would be made of iron and the wheels made of steel? If the wheels had actually been made of iron, would they be quickly worn down and rendered useless on the steel rails? Obvisously, there are less forces involved on a mining-rail than on a modern train-rail. But still, mining-wagons loaded full with stone and frequently going back and forth from the surface to the innermost depths of the mine could possibly be very taxing on iron wheels against steel rails, no?

Krikkert7 (talk) 16:45, 8 March 2014 (UTC)

Minecart shown in De Re Metallica (1556). The iron guide pin fits in a groove between two wooden planks. Railroads descended from minecarts. 84.209.89.214 (talk) 00:53, 9 March 2014 (UTC)

The first rails were made of wood. The 'trains' were actually wagons pulled by horses. In the XVIII century, the wood was substituted by iron, both on the wheels as on the rails.

The first trains were funicular, so part of the weight was being carried by the cable, not by the wheels. OsmanRF34 (talk) 19:21, 8 March 2014 (UTC)

There are actually several different standards for railway tires per ASTM A551, based on whether it's a passenger train, freight train, switching locomotive, or rapid transit train. But all of them are basically low-alloy, medium/high carbon steel. The composition spec for passenger trains would correspond to AISI 1050. Switching/rapid transit would use AISI 1080. Both are basically 98+% iron, so it's not a particularly expensive alloy. The strength is a result of the heat treatment. Stopping/starting and wheel slip seem to be more relevant for wear. Mr.Z-man 20:09, 8 March 2014 (UTC)

You seem to know your way around train-wheels. Impressive, and your links were educational ones - I did read through them. But mining-wagons is what I am looking at really, not trains, and if you have some knowledge about that or some sources/links to share I would be more than happy for it. Krikkert7 (talk) 00:01, 9 March 2014 (UTC)

A lot of rail technology was originally developed for mines, so there's a lot of overlap in the history. Prior to around 1850 when the Bessemer process was developed, steel was rather expensive. As OsmanRF34 said, early railways used wood. Cast iron started to appear around 1790, but was brittle and uneven. Wrought iron rails were invented in 1820 by John Birkinshaw. So the material used would likely depend on the time:

Pre-1700 would have almost certainly been wood for both the rails and wheels.

At some point (~1730-1750) they started putting cast iron plates over the wooden rails, then cast iron wheels, then fully cast iron rails.

The brittleness of cast iron means they would have switched to wrought iron rather quickly around 1820. Cast iron rails were probably used mostly in mines; they were almost unusably brittle for steam engines.

By 1900 they were almost certainly using steel, which worked even better than wrought iron and was rapidly becoming cheaper.

For mines, where comfort and speed weren't really a concern, cast iron may have stuck around a bit longer for the wheels because it was cheaper. In trains that used a wheel/tire design, they often used cast iron wheels with wrought iron tires; though most of the pictures that I can find of old mine carts look like 1-piece designs for the wheels. But by 1900 or so, steel was cheap enough that its benefits (higher strength, less brittle) probably outweighed the cost vs cast iron. Note that neither cast iron or wrought iron are pure iron. Pure iron is as soft as brass and is expensive to make. Cast iron has a high carbon content (>2%) and is usually brittle. Wrought iron reduced the carbon content, and was similar to steel except for slag inclusions. For further reading: Wagonway, Mine railway, History of rail transport. Mr.Z-man 02:12, 9 March 2014 (UTC)

Another thing to consider is that if something is going to wear down, it's better to be able to just have regular maintenance schedule of changing wheels on the wagons rather than have to close the mine for a complete rail change. I operate a marine railway, where the underwater rails are extremely expensive to replace. The most important source of damage on any fairly low speed rail system is corrugations on the rail surface. (They form in a similar manner to corrugations on a gravel road). This is at it's worst when wheel diameter and the wagon speed are constant. We can't grind our undersea rails flat from time to time, the way the suburban rail operators do to prevent this, so if we could find a source of wheels that wore out rather than damage the rails, we'd jump at it! Tom duF (talk) — Preceding undated comment added 07:32, 9 March 2014 (UTC)

Would it be possible for you to use tempered rails but annealed wheels? That could reduce the wear and tear on the rails, if you can get the right components. 24.5.122.13 (talk) 09:13, 9 March 2014 (UTC)

Thanks a lot for all the answers. I didn't expect this much response. Tom DuF, You repair boats then? I'm sure you know of what you speak, but I would have thought that if wheels were made of iron and rails were made of steel, which is obviously an upgrade from iron and stronger, then wheels would be worn out first. I'm sure you can see the way of my thinking. A ship can also weigh a lot, depending on its size as well as other things, so the rails will probably have to endure a lot. But as I said, in your line of work you probably know a thing or two about how weight, pressure and frequent use can effect the metal over time. It's something to think about. Thanks again. Krikkert7 (talk) 16:02, 9 March 2014 (UTC)

See also our article Plateway about early iron rails. Richard Trevithick is generally credited with inventing the railway locomotive, but sadly, nobody had invented wrought iron or steel rails that it could run on (it broke the cast iron rails at the Merthyr Tramroad). Alansplodge (talk) 16:13, 10 March 2014 (UTC)

Could matter fusion itself generate the additional gravitational attraction that we call Dark Matter?

Hi All, Imagine that every instance of atomic matter fusion generates an attractive force to all other instances of atomic matter fusion. In this case, a star containing so many instances of fusion per second would be attracted to all the surrounding stars. Because each star nearby contains so many instances of fusion. Has nuclear fusion research advanced to the point where this possibility can be ruled out? Or does this fusion-causes-gravitation remain a possibility? Just curious...

(This is a thought in response to dinosaurs-done-in-by-dark-matter that talks about the Sun traveling up and down through the galactic plane on the order of every 15 million years or so...)

Thanks --InverseSubstance (talk) 23:46, 8 March 2014 (UTC)

What makes dark matter noticeable, I gather, is that its distribution differs from that of visible matter such as stars. —Tamfang (talk) 00:07, 9 March 2014 (UTC)

Agreed. We know how much gravitational attraction comes from the Sun, and if it was more than expected from the Sun's mass, we would have noticed that. The same is true of other stars. The hidden gravitational attraction seems to mostly come from the space between the stars. StuRat (talk) 17:48, 9 March 2014 (UTC)

If the Sun's gravity exceeded what we expect of its mass, we'd overestimate its mass. How would we know it's wrong? —Tamfang (talk) 07:41, 10 March 2014 (UTC)

Now that we understand how nuclear fusion works, we can estimate from the spectra of helium, hydrogen and accumulated fusion byproducts in sunlight what's in the Sun, and from observations of its size we can extrapolate its mass as a function of its volume and what we can deduce is its density (from estimates of its probable composition). This gives us a useful way of validating estimates of the Solar mass. loupgarous (talk) 04:38, 12 March 2014 (UTC)

That idea hugely violates the equivalence principle, so it would have very easily noticeable consequences that aren't actually observed. So no, I'm afraid it doesn't work. --Amble (talk) 07:06, 10 March 2014 (UTC)

Ah, the equivalence principle answers my above question: the Sun's movement about the Solar System's center of mass gives us the ratio of its inertial mass to that of Jupiter; this ought to be equal to the ratio between their gravitational masses, but wouldn't be if there were another way to generate Solar gravity. —Tamfang (talk) 07:47, 10 March 2014 (UTC)

The OP might not be wrong, if the fusion is generating sterile neutrinos. Though I don't really know where those come from, if they come from anything ... maybe supernovas? [3] but I'm getting the feeling some other mechanisms (boson decay, inflatons??, oscillations?) have more to do with it? Wnt (talk) 13:54, 10 March 2014 (UTC)

That's not quite what the OP said, but it also won't work. Starting from primordial hydrogen + a little bit of helium you'd need stellar fusion to have processed 90% of the initial mass of the galaxy into sterile neutrinos. We'd have noticed if fusion converted 90% of the mass-energy of the inputs into an undetectable sterile neutrino. --Amble (talk) 14:26, 10 March 2014 (UTC)