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August 18[edit]

Conclusions of an autopsy[edit]

A recent case got me to thinking about what information can or cannot be concluded from an autopsy. So, two questions. (1) Can an autopsy determine if the decedent were moving (e.g., running) versus standing still when the decedent was shot? And (2) Can an autopsy determine the position of the decedent's body when he was shot (e.g., whether or not he was holding his hands up in a "surrender" position?)? If indeed the medical examiner can make conclusions about these two matters, how would he do so? Thanks. Joseph A. Spadaro (talk) 04:25, 18 August 2014 (UTC)

The position of the body should show if he was running (unless he survived for some time after being shot and changed his position). Also, if he was running on a road or sidewalk, you'd expect abrasions where he slid on the cement. On grass his clothes should have grass stains. And the path of the bullet through the body would reveal the position of the part of the body it hit. If the body was vertical at the time, that would tend to indicate standing, while if it was angled, that would indicate running (accounting for the height and distance at which the bullet was fired).
Detecting the hands up position would be a lot trickier. If the shooter was close enough that the victim was sprayed with gunpowder residue, then the location and density of the spray would indicate that the hands were up, but with a distance shot this method wouldn't work. Blood spatter from the victim could be used in a similar way, but there might not be much spatter, especially if the bullet is small, doesn't exit the body, and the victim was wearing thick clothes, like a winter coat. On the other hand, with a case like the fatal JFK head shot, there was all kinds of spatter to work with. StuRat (talk) 04:57, 18 August 2014 (UTC)
Thanks. But, I still have some confusion. You said: The position of the body should show if he was running. Why is that? Once you are shot, don't you just sort of "plop" down, regardless of whether you were running or standing still? You also said: Also, if he was running on a road or sidewalk, you'd expect abrasions where he slid on the cement. When your body hits the ground, wouldn't you get abrasions either way, whether running or standing still? Thanks. Joseph A. Spadaro (talk) 05:31, 18 August 2014 (UTC)
At the very least, if he was hit in the back instead of the front, that would indicate he was leaving the scene. ←Baseball Bugs What's up, Doc? carrots→ 06:52, 18 August 2014 (UTC)
In the specific case of Shooting of Michael Brown, that doesn't seem to be a significant factor. Okay there are suggestions from witness statements that he was shot in the back, which may be problematic if there's no evidence of sufficient risk to anyone at the time to justify such a shooting. But although it's difficult to say since we only have third party reports of the officers account, the main dispute, as I think the OP knows appears to be whether he was kneeling on the groundfacing forward but not moving instead surrendering to the officer, or rushing towards the officer at the time of the fatal shots, after an earlier alleged attempt to grab the officers gun, before he started to run away. Nil Einne (talk) 08:02, 20 August 2014 (UTC)
Momentum is a factor here. If the victim is moving quickly, they will keep moving quickly after being shot (unless shot with something large and fast enough to cancel out their forward momentum). I'd expect there to be a difference between abrasions resulting from a straight fall down or backwards, and abrasions resulting from a fall when running, which results in sliding across the ground for a small distance. MChesterMC (talk) 08:41, 18 August 2014 (UTC)
Moment of inertia seems appropriate, as well. Though I'm what "laymen" call an idiot, sometimes. InedibleHulk (talk) 22:02, August 18, 2014 (UTC)
A-ha. That all makes sense. Thanks! Joseph A. Spadaro (talk) 08:49, 18 August 2014 (UTC)
As for the abrasions, you'd expect them to be longer and deeper if the victim was running when they dropped on cement or stones, or for the grass stains to be darker and longer if they dropped on grass. Of course, if the wounds weren't immediately fatal, they might have stopped running before they dropped. Regarding the angle of the bullets, the first should best show the initial position of the victim, but with rapid firing the victim's position might not change much between shots. StuRat (talk) 17:07, 19 August 2014 (UTC)
  • The problematic word here is "concluded" the medical examiner will describe a bunch of facts, that a bullet entered in one location and exited at another, that certain wounds were found, perhaps any signs of intoxication, cause of death (blood loss, brain trauma). It will be the forensic specialists who argue the case in court who will try to convince the jury of their theories of what happened. They will argue the patterns show he must have been standing, running away, shot while falling, etc. μηδείς (talk) 16:48, 18 August 2014 (UTC)
A medical examiner can conclude lots of things, as Steven Hayne illustrated. —Tamfang (talk) 20:03, 18 August 2014 (UTC)
Of course, he can conclude all sorts of things, such as cause and approximate time of death, type of weapon used, trajectory of a bullet though the body. He can have his own theory, if asked to testify as a witness. But he can't conclude guilt or criminal fact in the legal sense, which is what the OP seems to be getting at, given the recent shooting in MO. μηδείς (talk) 22:13, 18 August 2014 (UTC)
Though, of course, he may be getting at The Huston Plan. Inconclusive, I declare. InedibleHulk (talk) 22:20, August 18, 2014 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 21:03, 19 August 2014 (UTC)

Mayer bullets[edit]

Mayer bullets compared to an AA battery

There is an article on Russian Wikipedia about something called Mayer bullets or Mayer slugs. According to Google translate the article seems to say these are used in shotguns. How does that work exactly? Is a cartridge full of propellant loaded behind the slug? Are the Russians still using muzzle loaders? Our article on shotgun slugs seems to show the slug always crimped to a shell, but in the images in the Russian article just shows the slugs by themselves. SpinningSpark 10:48, 18 August 2014 (UTC)

My guess is that they are a normal type of slug, normally fired from a complete shell. I think they are just pictured solo for illustrative convenience. If you do an image search for shotgun slug, you'll see lots of photos where the slugs are removed from the shell for comparison purposes. Here's an article all about modern slugs, and it mentions a guy named Mayer, but it's probably not the same Mayer [1] SemanticMantis (talk) 14:58, 18 August 2014 (UTC)
Yup, not the same Mayer. That's Steve Mayer of Winchester, we're looking for A. K. Mayer (А. К. Майера) who invented a slug in 1963. SpinningSpark 16:22, 18 August 2014 (UTC)
They certainly seem to be on sale as bullets only without a shell [2][3]. SpinningSpark 16:54, 18 August 2014 (UTC)
@Spinningspark: I found a video where a guy is shooting them. I have no idea how they are commonly sold, but he shows the single slugs, then packs one into a shell, then fires it from a seemingly normal Break_action shotgun [4]. This video seems to be the same guy, and shows a little more about how the shell is assembled [5]. I found the videos by searching /Майера ружье/, with the second word meaning "shotgun" in Russian, according to google translate. SemanticMantis (talk) 21:58, 18 August 2014 (UTC)
Thanks, that about answers it then. SpinningSpark 23:57, 18 August 2014 (UTC)

Nuclear contrail thingies[edit]

Upshot-Knothole GRABLE.jpg

Yeah, I'm sure that's not the correct term, but since I have no idea what they are, I also have no idea what their name is. You can see them in the image at right; I've seen better images of them before but wasn't able to find any with a quick check of Commons. They are quite distinct white-ish lines of what look like water vapor, and they seem to have a strange habit of appearing in the area of nuclear weapon tests. I have a guess as to what they are, but it's probably wrong, and I'm sure someone here knows. Thanks in advance! Evan (talk|contribs) 16:05, 18 August 2014 (UTC)

They are smoke trails from small rockets launched just prior to the nuclear detonation. The visual distortion of the trails provides information about the detonation. Trying to find the relevant articles... DMacks (talk) 16:11, 18 August 2014 (UTC)
Mentioned with cite at Effects of nuclear explosions#Other phenomena. I know I've seen more detail of the history of this use (originally discovered accidentally!). DMacks (talk) 16:21, 18 August 2014 (UTC)
Fantastic! Thanks for the speedy response. Evan (talk|contribs) 16:24, 18 August 2014 (UTC)
How about an entire book on the history and role of such rockets? NASA Sounding Rockets, 1958-1968: A Historical Summary. This book focuses on civilian sounding rockets, including many that were fired at White Sands, but if I recall, it also has a section on the early Army rockets launched during the Trinity test in 1945. The photograph posted in the original question is a 1953 test at a different Department of Energy facility, the Nevada Test Site. Those sounding rockets were almost certainly small Army rockets and their smoke-trails would have been used as an indicator of the winds aloft (after the blast) at various distances. For some tests, the rockets would also be equipped with radiological, physical, and chemical detection and sample-collection equipment. You can find historical records of such tests from the Nevada Test Site's OpenLibrary web-page, hosted by the Department of Energy's Office of Scientific and Technical Information. In just a few moments of browsing, I found a technical report on the specific purpose of sounding rockets during Operation Hardtack, Aircraft and Rocket Fallout (1959). If you're interested in the exact test pictured above (Upshot-Knothole Grable, (1953)), I'm sure you can spend a few more hours browsing those resources. Nimur (talk) 17:16, 18 August 2014 (UTC)
Sounding rocket.    —E: (talk) 17:41, 18 August 2014 (UTC)
Here is the accidental first use of visual effect I was remembering: File:Trinity explosion film strip.jpg. And according to ISBN 9783540304210 page 992, the smoke trails are actually not even from really rockets, just simple mortars (in this context they are only used for the smoke trails, not the object being lofted). DMacks (talk) 16:57, 19 August 2014 (UTC)

Water jet cutter as a weapon[edit]

About how effective would a water jet cutter be as a weapon?(ignoring the bulk of the surrounding hardware) Would the stream just dissipate into steam after a few feet? (talk) 16:37, 18 August 2014 (UTC)

Our article does say "The penetrating power of these tools has led to the exploration of their use as anti-tank weapons but, due to their short range and the advent of composite armour, research was discontinued.[citation needed]". Rojomoke (talk) 16:45, 18 August 2014 (UTC)
Yeah I saw that, but ya know. Citation needed, plus I want to know what causes the range to be limited. (talk) 16:57, 18 August 2014 (UTC)
Air resistance and turbulent flow limit the effective range at which you can shoot a stream of high-velocity liquid. You read a two-sentence overview at the terminal velocity section of our article on water drops. Momentum and energy - which you would want to direct into the target - are instead lost to the air around the stream of water as it "sloshes." The faster you move the water, the more it sloshes, because air flowing past the "edges" of the water stream induces a viscous flow shear force. Nimur (talk) 17:02, 18 August 2014 (UTC)
I remember reading that in the article when I first started at my current job (we have a waterjet cutting machine) and pointing it out to a colleague who laughed. When it comes to steel, particularly thicker/harder steel, it is very slow. To give some numbers, the M1A2 Abrahms tank apparently has armour 120mm thick (according to google, yeesh), the feed rate for that thickness is somewhere in the region of 2-3mm a minute. That means to cut through 1m of steel would take some 6-8 hours. In that time your tank could have driven 250-340 miles--Jac16888 Talk 17:34, 18 August 2014 (UTC)
The rate at which the machine could cut a slot might not matter if you could aim it sufficiently well - a single penetrating hole one millimeter in diameter would be plenty if you can hit exactly the right spot in the engine bay and have the water jet drill a 1mm hole through some vital engine part or electronics. But I agree that keeping the water flow focussed over significant distances would be the downfall of such a weapon. I doubt that it's practical beyond a foot or two. SteveBaker (talk) 20:27, 18 August 2014 (UTC)
1mm could take 30 seconds, which a long time considering at the same time a tank-turret is probably turning around to face you--Jac16888 Talk 21:48, 18 August 2014 (UTC)
That sentence, which evolved out of something posted by someone at Central Michigan University in 2007, was apparently inspired by the use of a water jet cutter in the video game Metal Gear Solid 2. See the original addition. I can't find anything using Google that would support that sentence, so I removed it. Red Act (talk) 20:32, 18 August 2014 (UTC)

Would shooting another liquid that has a higher density and/or boiling point at high velocity make a difference? Liquid metal perhaps? (talk) 22:31, 18 August 2014 (UTC)

You're on the right way, since most portable anti-tank weapons use metal, which behaves like a liquid at the kind of pressure involved. Generating that kind of pressure (I've read it's in the TPa range[citation needed], which is more than 107 times atmospheric pressure) using non-destructive equipment (in the sense that it doesn't blow itself apart in the process) is difficult even with today's technology. Sidney Alford#Early Inventions lists some shaped charges using water, so the idea isn't flawed as much as it hits its limits if applied to modern armor.
Also note that a [citation needed] tag does not necessarily indicate that the tagged statement is dubious; it indicates that a key fact is not backed by a source in the list of references. For dubious statements, we have the [dubious] tag. - ¡Ouch! (hurt me / more pain) 05:49, 19 August 2014 (UTC)
It is a common application in manufacturing engineering. See Water jet cutter. It only works on very short distance but is a very cost efficient, precise, fast and reliable technology to cut flat materials like steel plates. But it wouldnt make much sense as a weapon. --Kharon (talk) 16:51, 19 August 2014 (UTC)
Note that shaped charges don't work either if the range is too high or too low. If the distance between charge and target surface is off, the effect can be severely diminished or even completely fall flat.
From Shaped charge: The location of the charge relative to its target is critical for optimum penetration for two reasons. If the charge is detonated too close there is not enough time for the jet to fully develop. But the jet disintegrates and disperses after a relatively short distance, usually well under 2 meters. At such standoffs, it breaks into particles which tend to tumble and drift off the axis of penetration ; OTOH, a water jet cutter wouldn't work well even at 1m, where the shaped charge only begins to exhibit severe degradation. - ¡Ouch! (hurt me / more pain) 08:33, 20 August 2014 (UTC)

In the Yom Kippur War, very low tech predecessors of the water jet cutter were efficiently used as weapons by the Egyptian army on the Bar Lev Line. --Dweller (talk) 12:14, 21 August 2014 (UTC)

Kidney function questions[edit]

A complicated process. :)

The other day I started wondering about kidney function. Firstly, does the filtering ability of the kidneys dynamically respond to waste concentrations in the blood? If a person happens to have high levels of urea, or salt, or something else in their blood does the body have the ability to increase the activity of the kidneys, or are they pretty much going to filter the blood at a fixed rate regardless? Secondly, for a fixed level of hydration, if one has more waste in the blood (e.g. urea / excess salt) does that lead the kidneys to excrete more water as well or is the water output about the same but the waste in the urine more concentrated? Dragons flight (talk) 23:10, 18 August 2014 (UTC)

First of all, it's important to clarify that the kidney only removes excess organic molecules and/or wastes. The answer to your first question, as far as I can tell, is yes. Refer to Clearance (medicine). Not sure about the answer to your second question, sorry. ceranthor 00:25, 19 August 2014 (UTC)
The removal of waste and water are largely independent (although obviously some water is needed to carry the waste out). If you drink a very large quantity of water, but don't eat much or do much, your urine will be clear, since it's mostly water. If you are dehydrated, but have eaten a lot and done a lot of exercise, your urine will be brightly colored, since it's much more concentrated with waste. Obviously that wouldn't be a safe test, but you can take some vitamin C, instead. That will turn your urine brighter yellow, which indicates it has a higher concentration of waste (vitamin C, in this case).
I suspect that salt is a special case, though, where the concentration of salt in the urine can't be changed much relative to the concentration in the blood. This would explain why eating salty things makes you thirsty, because the salt must be diluted, as it can't easily be removed at high concentrations. StuRat (talk) 00:38, 19 August 2014 (UTC)
I would suggest conceptualizing the kidney as an organ of absorption rather than merely excretion. For the example of Vitamin C, one should realize that all the vitamin C in the serum passes into the renal tubules, and then only a certain amount is reabsorbed. So the kidney isn't responding to a high level of vitamin C and excreting more, it's just excreting all the vitamin C regardless of its blood level, and then reabsorbing the same amount it always does. Salt, as StuRat says, must be considered separately, as it's not a simple matter of passive diffusion; there are a variety of means of regulating salt (active transport, hormones, countercurrent multiplication, etc.). You may be interested in the concept of obligatory water loss, which is the amount of water that must be excreted in order to remove waste products and thereby maintain health. - Nunh-huh 01:01, 19 August 2014 (UTC)
I see we don't have an article on obligatory water loss, but you will find a brief mention in dehydration. - Nunh-huh 01:01, 19 August 2014 (UTC)

Let's take a step back here. Kidney function starts with what seems to be a pretty straightforward filtration in Bowman's capsule, (lovely illustrations in our article!) where most contents of the serum (but not proteins) are allowed to escape into the system. Then here is more activity proximal convoluted tubule where more things can be specifically excreted into this ever-flowing stream. Then this, the loop of Henle and distal convoluted tubule remove things that you want to keep, like water and salt, and finally what is left is collected and dumped. All of this is massive generalization, since each and every cell is a tremendously complicated living thing capable of a vast range of behavior; you'd really have to look up for your molecule of interest what happens. But urea and salt are on the diagram I've added at the top of this section. Note of course that every process done to a solute - filtration, secretion, reabsorption - will tend to be influenced by the internal concentration of whatever it processes by Le Chatelier's principle, linearly if it follows a first order relationship, otherwise in some more complicated way. But it generally is more complicated; the kidneys have primary responsibility for keeping many of the overall concentrations of things in the blood, especially ions, at the right values. For example an ACE inhibitor for high blood pressure ultimately affects sodium reabsorption in the kidney (see angiotensin). Wnt (talk) 12:58, 21 August 2014 (UTC)

August 19[edit]

Lowest Possible Temperature[edit]

We know there is a lowest possible temperature, but is there a theoretical highest? KägeTorä - () (Chin Wag) 01:18, 19 August 2014 (UTC)

WHAAOE. Absolute hot. --Jayron32 01:20, 19 August 2014 (UTC)
There's also negative temperature. Dmcq (talk) 16:09, 19 August 2014 (UTC)
So, if a system at negative temperature is brought into the presence of a system at absolute hot, which way will heat flow? The article says " If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system." - but I have no idea if that applies to absolute hot... SemanticMantis (talk) 16:52, 19 August 2014 (UTC)

Atoms as fact[edit]

When did the scientific consensus become that atoms are real? I read atomic theory, but it doesn't mention any point in time or event. Bubba73 You talkin' to me? 04:20, 19 August 2014 (UTC)

See there about Dalton in the section 'First evidence-based theory' and his presentations of the atomic theory at the start of the nineteenth century. His first oral presentation in 1803 is one good date and his textbook in 1808 is another. Dmcq (talk) 08:03, 19 August 2014 (UTC)
The term "atom" or "indivisible particle" was revived 1805 from ancient Greek philosophical speculation by John Dalton. In 1828 "atom" was evidently part of Christian truth with which Noah Webster was concerned in his dictionary. Understanding of the atom has progressed from the cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911) to the Rutherford–Bohr model or just Bohr model for short (1913) whose image is most recognized today. The Bohr model is widely taught as real and gives an explanation of some spectral emissions. It may be said to have reached popular consensus though scientific consensus favours the quantum mechanical atomic model introduced by Wolfgang Pauli in 1925. (talk) 10:41, 19 August 2014 (UTC)
First of all, scientists don't think in terms of "facts" and "proof". The think in terms of "evidence". Dalton's atomic theory was well a well accepted conjecture by the middle 19th century, but the definitive empirical justification ("proof" if you want) is usually cited as Einstein's paper on Brownian motion in 1905 (his Annus Mirabilis. See Annus Mirabilis papers). The other parts of atomic theory, those dealing with the internal structure of atoms, built up over time, with the experiments and conjectures cited above by, who did a great job laying out the history of Atomic theory. There were also some false starts in Atomic theory, see Prout's hypothesis for a more famous one. --Jayron32 14:09, 19 August 2014 (UTC)
That is kind of what I was getting at. The 19th century chemists had a model that worked beautifully, but I don't think any of them "detected" an atom. Bubba73 You talkin' to me? 02:56, 20 August 2014 (UTC)
I'm sure I have read somewhere that atoms were widely accepted among scientists as a model by 1905 but there were still some who didn't. Einstein's Brownian motion paper which provided another way to calculate the size of atoms was an extra bit of useful evidence that atoms existed and weren't just an apparent building block of solids that was actually made up of other things of different sizes. (oops should have read Jayron's answer first) JMiall 18:53, 19 August 2014 (UTC)
There is a subtle confusion here. Once the experimental results were in and the math had been crunched, it would have been valid to say "The world operates as if matter was made of atoms" - but you still wouldn't know that there actually ARE atoms. These days, we've actually imaged them so we have direct evidence - but that's a rather recent thing. SteveBaker (talk) 05:24, 20 August 2014 (UTC)

Can you accelerate the decay of radioactive material?[edit]

Or do you always have to bury it and wait 10,000 years? OsmanRF34 (talk) 15:10, 19 August 2014 (UTC)

For practical purposes, decay rates for spontaneous radioactive decay are constant. Radioactive decay#Changing decay rates says "The radioactive decay modes of electron capture and internal conversion are known to be slightly sensitive to chemical and environmental effects that change the electronic structure of the atom, which in turn affects the presence of 1s and 2s electrons that participate in the decay process. A small number of mostly light nuclides are affected ... A number of experiments have found that decay rates of other modes of artificial and naturally occurring radioisotopes are, to a high degree of precision, unaffected by external conditions such as temperature, pressure, the chemical environment, and electric, magnetic, or gravitational fields". Gandalf61 (talk) 15:22, 19 August 2014 (UTC)
The key words here are *spontaneous* radioactive decay. While temperature, pressure, electromagnetic fields, etc. don't substantially increase decay rate, neutron flux will. See Nuclear transmutation#Artificial transmutation of nuclear waste for details. -- (talk) 16:21, 19 August 2014 (UTC)
Well surprisingly you can just about do the opposite see Quantum Zeno effect. And of course sending particles at something will start splitting it up, a nuclear bomb is a good example. Dmcq (talk) 16:02, 19 August 2014 (UTC)
You can sort of do that partly, by refining the material aka split it up into active and decayed matter with physical and/or chemical methodes of process engineering. This is actually done to an limited extend for some Time with radioactive waste because in most countries space in radioactive waste repositories is very expensive. --Kharon (talk) 16:35, 19 August 2014 (UTC)
You should be able to change a radioactive isotope into something else by bombarding it with enough of the right type of radiation. However, it may turn into something even nastier. Also, you are likely to get many different products, so now you need to separate the stable from the radioactive. There's also the risk that you might get more heat than anticipated, due to unknown interactions between all the products and radiation, and have an explosion or meltdown. StuRat (talk) 16:56, 19 August 2014 (UTC)
If you want to accelerate the decay, that means you want something "even nastier". Things that decay slowly are not very radioactive. But as Stu says, the problem is that you are likely to get many different products. I don't believe it's practical at present to convert all of a chunk of some substance into another by irradiating it. -- (talk) 00:24, 20 August 2014 (UTC)
It is possible using fast breeder reactors, but the anti-nuclear movement has stopped the development of large scale nuclear power making fast breeder reactors uneconomical at present. The Integral fast reactor was never completed, the article says: "Fast reactors can "burn" long lasting nuclear transuranic waste (TRU) waste components (actinides: reactor-grade plutonium and minor actinides), turning liabilities into assets. Another major waste component, fission products (FP), would stabilize at a lower level of radioactivity than the original natural uranium ore it was attained from in two to four centuries, rather than tens of thousands of years." Count Iblis (talk) 17:34, 19 August 2014 (UTC)
Giant resonance does not need fast breeding reactors or other sources of neutrons. But probably prohibitive amounts of energy. (talk) 19:12, 19 August 2014 (UTC)
Another option is to separate out the radioactive isotopes from the non radioactive material. This my make a valuable resource, or at the least make a smaller waste output. Graeme Bartlett (talk) 23:10, 19 August 2014 (UTC)
What if extremely strong magnetic fields are used to deform the core atomic orbitals? Will that not affect the stability of the nucleus toward certain types of decay? Plasmic Physics (talk) 00:16, 21 August 2014 (UTC)

Decline of large aerial predators[edit]

The amount of large aerial predators seem to be nonexistent, which is counter-intuitive to me. Considering there used to be creatures with wingspans the width of a basketball court, what led to their extinction? Considering there are still whales and elephants, it seems weird to me that bustards are the largest bird left around, with no large bird-of-preys. Was it tied to lowered oxygen levels? Climate change affecting updraft? Trees growing taller to hide prey? Just curious. --Wirbelwind(ヴィルヴェルヴィント) 19:26, 19 August 2014 (UTC)

No large birds of prey? Tell that to the harpy eagle or the golden eagle. Here's a nice video about the harpy eating monkeys [6], and here's one about the golden hunting wolves [7]. As for the biggest flyers ever, what do you know of with a ~50 ft wingspan? (the width of a basketball court). Pterosaur_size tops out at ~35 feet, according to our article. The largest bird we have evidence of is currently Pelagornis_sandersi, which, with a wingspan of ~20 feet is admittedly ~2x the wingspan of our current leader, the wandering albatross. But enough with questioning your premise:
You're right that were some larger flyers in the past, but there were also lizard type things the size of school buses, and they went away too, most likely due to the Chicxulub impact. So the pterosaurs et al. went extinct due to massive disruption of the food chain, as all photosynthesis on earth was severely compromised for a long time (more info at dinosaur extinction). After that, everything was much smaller, and there was a lot of value on the R side of R-K selection. Now, we might ask the question, "why have no very large flying predators evolved again?" I think the key here is that size is relative. We lost most of our megafauna in the Holocene extinction, and even though that was pretty recent, things have pretty much stayed smaller since then. I don't personally think O2 levels or updraft patterns are the culprit, but that's hard to find references to support. Even though the Square-cube_law has never changed, I think its importance might be strengthened in a world with much more pathogens, complex food webs, greater diversity of terrestrial vertebrates, etc. The main thing to think of is the ecological niche, and, for whatever reasons, the niche space is just not there anymore, even if it used to be. SemanticMantis (talk) 20:13, 19 August 2014 (UTC)
I wasn't aware of golden eagles hunting wolves, but that does seem like a partially human-influenced behavior. Looking at the statistics in the article, the most commonly hunted canid is the fox, which still comprises of a tiny percentage. As for the 50' wingspan, blame National Geographic (or similar) for that figure. It was compared to a basketball court in a documentary. As for everything shrinking, I'm aware of that. I just meant it's counter-intuitive (maybe only) to me that aerial predators haven't thrived due to a lot of advantages flight should bring. --Wirbelwind(ヴィルヴェルヴィント) 22:11, 20 August 2014 (UTC)
A giant asteroid slammed into the Gulf of Mexico some 65 million years ago, setting off a chain of catastrophic events that ultimately led to the extinction of all big living creatures. Then mammals got bigger. And eventually they paid the price. Several mammoths and other big mammals died off during the Pleistocene/Holocene extinction event, which started around 50,000 years ago. whales were more mobile and could emmigrate to whenever they wanted. Animals bigger than elephants didn't have so much luck. If there is little food, you are better off being small and having lots of descendants as fast as possible. OsmanRF34 (talk) 20:19, 19 August 2014 (UTC)
Thank you. This is more or less the kind of answer I was looking for. --Wirbelwind(ヴィルヴェルヴィント) 22:13, 20 August 2014 (UTC)
Per Semantic Mantis, there are several birds of prey which can be strikingly large; it's just that humans rarely get up close to them to see them. All animals (aside from whales) are generally smaller than they were in the Mesozoic era and flying critters are no exception. However, that doesn't mean that all birds are pigeon-sized. Female bald eagles have a length of 3.5 feet or so (standing on the ground they'd come up past your belly button) and have a wingspan of 7.5 feet or more. The golden eagle noted by Semantic Mantis above can get even larger. Those are land-based raptors. Seabirds can also get pretty large; various kinds of pelicans can get as large as a person; 5+ feet in length with an over 8 foot wingspan. Obviously, they weigh less than people, but they are still quite big in size (bird physiology maximizes their ability to fly, and so tends to favor lower mass-to-size ratios than land animals). The grand-daddy of carnivorous birds is the California condor, which is a bit shorter than the largest pelican, but can have up to a 10-foot wingspan. Again, since most people never see one of these birds up close, it can be hard to judge them from context. If you ever do get to see one up close, it takes you aback at how big they can be. --Jayron32 22:00, 19 August 2014 (UTC)
When it comes to pterosaurs, this is an open question. There is even a question about the question itself. Based on the fossil record, it appears that the pterosaurs reached peak diversity in the early Cretaceous period and then sharply declines before being finished off by the K-Pg extinction. However, it's possible that at least some of this apparent decline may be due to gaps in the fossil record ([8]). It should be noted that as far as we know, there were never any large, predatory pterosaurs (the thing with pterodactyls carrying prey off to their nest is a Hollywood invention;they didn't even have grasping feet, or bird-like nests). Why a highly diverse group like pterosaurs never produced any predatory forms is an interesting question and I'm not sure if it's been addressed. There may have been small hawk-sized predatory pterosaurs (this has been suggested for Darwinopterus), but even the biggest ones like azhdarchids seem to have been stork analogues, picking off small prey like lizards and baby dinosaurs. I guess that's still predatory, but maybe not the way most people think.
It's true that birds have not yet ever attained sizes comparable to pterosaurs and are on average very small (pterosaurs were on average very big as adults with no known tiny species, probably because they took years to grow up unlike birds, and niches for small sized animals were occupied by babies of larger species). It has been suggested that birds are limited in size by their takeoff style. They need two well-developed sets of limbs - forelimbs for flight, and hind limbs for launching themselves into the air. That's two well-developed sets of muscles in creatures that need to stay as light as possible. Pterosaurs were quadrupeds and most had piddly little hind limbs. By all accounts, they both launched AND flew with the forelimbs, allowing the biggest pterosaurs to get a few times bigger than comparable birds.
I don't think there have ever been any really large aerial predators. The largest I can think of is Haasts eagle, which isn't as large as the largest flying birds today, though larger than the extant predatory ones. All birds that ever lived larger than this have either been vulture-type birds (scavengers) or seabirds, which eat fish and can get larger than normal by taking advantage of oceanic winds to aid flight. Dinoguy2 (talk) 23:23, 19 August 2014 (UTC)
'Large, flighted, actively-hunting bird' is probably one of the most energy intensive animal 'designs' possible. Imagine how much food a 150lb+ bird that chased down and subdued live prey would need to eat in order to remain alive, let alone thrive, given that flying birds have a much faster metabolism than mammals (from what I've seen, birds tend to eat a huge amount for their size) - and how much territory it would need to fulfil its hunting needs. Such a critter would certainly find it difficult to survive and almost certainly be amongst the first to die out, should the world ever take a turn for the worse. The condors are huge and carnivorous, to be sure - but they are also mostly scavengers and gliders. --Kurt Shaped Box (talk) 23:36, 19 August 2014 (UTC)

This is not a scientific answer because there is lack of scientific evidence for it. But I believe that not only is the percentage of oxygen higher in the past but the air pressure is higher in the past as well. In fact I believe the air pressure is 10 times to 50 times higher in the past than the air pressure is today. Therefore with higher air pressure in the past, flying creatures can be bigger because it can generate bigger lifts. Of course, air pressures leaves no "fossil records" and thus I am not able to offer any proof that air pressure is higher in the past. (talk) 00:56, 20 August 2014 (UTC)

"This is not a scientific answer because there is lack of scientific evidence for it." So why post it? The OP asked a scientific question, so he presumably was not looking for weird beliefs based on fantasy as an answer. Might as well answer with "Well, in Middle-Earth, the air might have been like this..." People often feel the need to explain giant Mesozoic animals by invoking air density, air pressure, or differences in gravity, simply because they don't understand that the biology of these animals was different from any living today. We do not have any quadrupedal fliers with extensive pneumatic lungs today, because they were all killed by an asteroid. We don't have any land animals with extensive air sacs today either. If mammals had air sacs and R-selection breeding strategies, they could easily reach or exceed the size of dinosaurs, but they don't. No need to call on strange differences in air pressure or gravity with no evidence when we have plenty of evidence pointing to simple biological explanations. Dinoguy2 (talk) 13:28, 21 August 2014 (UTC)
We do not currently have a Thick atmosphere theory article, and Atmosphere of Earth#Evolution of Earth's atmosphere does not address pressure. (Faint young Sun paradox does discuss the posibilities of CO2 partial pressures as high as 10 bar, but long, long before the cambrian radiation, presumably only up until the GOE.) Here are a couple of interesting papers by Octave Levenspiel published in 2000 in ACS's Chemical Innovation: Earth’s atmosphere before the age of dinosaurs (with Thomas J. Fitzgerald & Donald Pettit, on the ACS site) and Atmospheric Pressure at the Time of Dinosaurs (on Levenspiel own site). -- ToE 05:01, 20 August 2014 (UTC)
According to Quaternary extinction event and given the many near extinct species, caused by overhunting and -fishing done by humans up till today, its almost certain there where some but Homo sapiens sapiens killed them all.
Even worse. Your contradiction regarding whales and elephants is wrong. We (as species) would likely have killed all whales and elephants by now if some international Commissions had not put a world wide ban on commercial whaling and ivory trading. --Kharon (talk) 02:37, 20 August 2014 (UTC)
It's also interesting to note that the only continent left with an in-tact megafauna is sub-Sahara Africa, which also happens to be the only megafauna that co-evolved with humans, and presumably evolved strategies to avoid human predation. It was only after large scale access to killing using cars and guns that they went into steep decline. Dinoguy2 (talk) 13:39, 21 August 2014 (UTC)

August 20[edit]

Wheel base anf friction[edit]

Can we say that wheel base is proportional to friction acting on a vehicle,when brakes are applied.I think i solved a problem in h c verma(12 class physics) using this assumption.please correct me if i am wrong.

Sameerdubey.sbp (talk) — Preceding undated comment added 03:38, 20 August 2014 (UTC)

Wheelbase is normally understood to mean the distance between the front and rear axles of a vehicle. Your statement accordingly makes no sense at all. AndyTheGrump (talk) 03:41, 20 August 2014 (UTC)

I appreciate your effort in commenting Grump.See google bookpg 371,there's a derivation that has wheel base in numerator and denominator as well.Then what do you say?whether frictional force would increase or decrease with wheel base. please read derivation and then comment.Bit engineeering involved. SD — Preceding unsigned comment added by Sameerdubey.sbp (talkcontribs) 07:12, 20 August 2014 (UTC)

Link is broken. yes there is a bit of physics involved, that's a high school physics problem judging by the search terms, but your question is at best very misleading, but answering the most likely rendition , you are wrong. Greglocock (talk) 07:55, 20 August 2014 (UTC)

Mr cock ,justify whatever you want to say.let it be high school physics. SD — Preceding unsigned comment added by Sameerdubey.sbp (talkcontribs) 09:58, 20 August 2014 (UTC)

[ was able to get the link to work, but google books is notoriously hard to link to... try this one maybe [9].
Anyway, as far as I can tell, the OP's claim is sound, if we understand it not to be about friction per se but the retardation in speed as the book calls it. The book uses D'Alembert's_principle to calculate the retardation of applied brakes in a three scenarios, 1)rear brakes, 2) front brakes, 3) all four wheels.
Basically, the wheelbase L comes into play because the car is going up an inclined plane, and the the brakes are only applied to the rear wheels in that example. This setup effectively creates a moment arm due to the fact that the center of gravity is above the plane containing the centers of the wheels. This should make intuitive sense: if the car is going uphill quickly, then brakes only using rear brakes, the car will start to lift at the rear, thus reducing the normal force on the rear wheels, thus diminishing the effect of braking. Using a very long wheelbase truck, e.g. a Ford F-650, this effective decrease in retardation will have lesser magnitude, compared to e.g. the same effect in a Mini.
Likewise, L appears in the solution to the front brakes only.In the later example of all four wheels braking, no L term appears. This book contains a bunch of fairly complicated and analyses of force diagrams, including some bothersome algebra and calculus. So, while not terribly "hard" math, it's more than I can work through and explain in a few minutes, which is all I have to spare right now :)
So, OP, you are not entirely wrong, and I'd give a gentle trouting to the above posters for assuming you were wrong without really looking for how you might be right! I still can't tell what your specific question is, nor can I check your answers. But the idea that the effect of braking, "retardation", can depend on wheelbase, is sound, provided that we are interested in the case of an inclined surface and brakes not applied to all wheels (or with different types of brakes on front and rear wheels, which used to be common). As the equations show, wheelbase can affect retardation in that scenario, but it is still incorrect to say the wheelbase is directly proportional to the retardation, because you cannot factor equation 8.24 into the form a=L*(a constant term), where a is the symbol for retardation. Hope that helps, SemanticMantis (talk) 17:43, 20 August 2014 (UTC)
Trout all you like, " wheel base is proportional to friction acting on a vehicle,when brakes are applied" is wrong. If you double the wheelbase of a typical vehicle (say cgz=0.7m, wb=2.6m) on a typical slope (up to say 0.25) then the frictional braking force at any axle is NOT doubled. Do the physics, no calculus required. The OP asked if he was right or wrong, he is wrong.Greglocock (talk) 22:13, 20 August 2014 (UTC)
Well, I did say a gentle trouting :) and I did specify that it is not correct to say that it's directly proportional. I'm assuming OP doesn't have English as a first language, and is also learning new physics. And based on the ref OP provides, it is true that wheelbase can affect braking effectiveness if not all four wheels have equal braking power. The equation in the book gives for rear-wheel breaking up an incline is  a_{retartadion}= \frac{(L-x)(\mu g \cos \alpha)}{(\mu h +L)} + g \sin \alpha. True, that is not what we call directly proportional, but there is a near linear dependence there. For certain values of the parameters (e.g. large L>>1, x <<1, 0< sin \alpha <<1 ), it is very nearly proportional. I mainly brought up trouting because I assumed from your response that you didn't even look at the OP's link before responding. SemanticMantis (talk) 00:20, 21 August 2014 (UTC)

Semantic is the man,thanks a lot!!,It means,i said the reverse.while riding a vehicle,without the brakes applied.I must say wheelbase is inversely proportional(Third Case) to the retarding force acting to bring vehicle to motion or keep it in motion.since braking force is proportional to (mu*constant/L),where L is the wheelbase(See the third case in Bookpg347).Now as L increases opposing force or braking force on vehicle decreases.Hence Low wheelbase vehicles are harder to bring into motion and less fuel efficient.Is it the thing Practically,i feel the reverse.What do u say? Mr.Cock be Human. — Preceding unsigned comment added by (talk) 03:18, 21 August 2014 (UTC)

I think you need to be careful about generalizing from the math shown in the book. While fairly detailed, this is still very much an idealized representation of car physics. Equation 8.26 is the conclusion of third case, where all four brakes are applied equally, and no L terms occur. There are L terms in the previous lines, but they eventually cancel out. I think L will only come into play for braking two wheels at a time, which isn't very common in the real world. I don't think this analysis will help you draw any conclusions about cars with small wheelbase being less fuel efficient. In the real world, smaller cars tend to be more fuel efficient in terms of miles per gallon, because they usually weigh much less. If you factor weight into your idea of efficiency, then perhaps some larger cars have a higher (miles)*(weight)/gallon. But for real world scenarios, there are far more details than included in your linked book. This is why things like mpg are tested empirically, not calculated from first principles of physics. Anyway, I hope I've helped clear up this example. If you have more questions I'd probably recommend starting a new thread, and spending a little more time composing your English. While I can understand you, it is a bit difficult to do so, and some people make the mistake of thinking poor English means the writer is not that smart ;) SemanticMantis (talk) 14:27, 21 August 2014 (UTC)
Actually due to tire load sensitivity in the real world there is always an L term present even with 2 axles braking and on a flat road, that is, weight transfer always matters. Greglocock (talk) 00:27, 22 August 2014 (UTC)

Velocity of Saturn's moons[edit]

Any of the many, doesn't matter - I'm writing a fantasy where there's a vehicle tethered to one of Saturn's satellites, towing it around one of the rings. My preference is for one of the Inuit, Gallic, or Norse moons, because their names are so cool, but I gather they're further out than the orbit of the rings.

Thanks for your indulgence

Adambrowne666 (talk) 04:42, 20 August 2014 (UTC)

Velocity relative to what? Saturn? If one end is tethered to the satellite, what's the other end tethered to? (It can't be Saturn, because it doesn't have a solid surface.) --Bowlhover (talk) 05:06, 20 August 2014 (UTC)
Note that if you have a tether running from the spacecraft to the moon, remember that you only need the tow to get the vehicle up to the speed of the moon - then you can cut the tether and the spacecraft will continue to follow the moon around. Of course the moon will have some tiny amount of gravity - so after that initial acceleration, you'd pretty much have a slack tether. So calling this a "tow" is a little confusing. SteveBaker (talk) 05:20, 20 August 2014 (UTC)
The statement that Saturn doesn't have a solid surface isn't entirely correct. Like Jupiter and the other gas giants, it does have a nickel-iron core, surrounded by a layer of ultra-dense hydrogen metal. The metallic hydrogen is probably a liquid, but the nickel-iron core is presumably definitely solid, and certainly has a surface. Saturn is mostly hydrogen all the way down, so the prevailing theory is that changes in pressure mean that the metallic core is surrounded by a giant hydrogen sea just beneath the gaseous layers we're familiar with. According to our article on Saturn, the transition from gaseous to liquid hydrogen occurs at such an altitude that 99.9% of Saturn's mass is within the pressure range for liquid hydrogen—so maybe we should be calling it a liquid giant. As an aside, some scientists now think that Jupiter and Saturn's magnetic fields are largely produced by this massive amount of metallic hydrogen, rather than by their fairly small nickel-iron cores.
Given strong enough materials, you could easily utilize the principle behind Clarke's space elevator to either tether something directly to the solid core, or to a buoyant object floating in that sea. Evan (talk|contribs) 15:54, 20 August 2014 (UTC)
This must be some meaning of the word "easily" of which I was previously unaware. SteveBaker (talk) 19:08, 20 August 2014 (UTC)
I am assuming, of course, that someone wants to spend the money necessary. Space elevators are completely possible given current technology; a simple tether (read: spaceworthy bit of string) would be even easier. Evan (talk|contribs) 19:33, 20 August 2014 (UTC)
No, space elevators are impossible with current technology, even on Earth. The only known material strong and light enough is carbon nanotudes, and it's not currently possible to make more than a few centimeters of it. See space elevator. --Bowlhover (talk) 05:19, 21 August 2014 (UTC)
I've read the article, but I think we're talking past each other. Carbon nanotubes seem to be the technology practical space elevators will require; the problem is manufacturing them in large enough chunks for a construction process of that magnitude. I look at that as a manufacturing (and not insignificantly, a funding) problem. I might have too much faith in science, but I struggle to imagine the world's scientific community failing to work out the manufacturing difficulties, given access to Apollo-project-style funding. "Impossible" is a strong word; "hasn't been done yet" is more appropriate. As an aside, space tether is another fun article. Evan (talk|contribs) 18:53, 21 August 2014 (UTC)
Which is totally irrelevant anyway, as I just noticed. Adam specifies that the satellite is tethered to a vehicle (though perhaps vice-versa would be more appropriate), and I'm thinking that means the vehicle is either in orbit around the satellite or trailing behind it (being towed) in the same orbit around Saturn. If the latter, then what you're looking for is the orbital velocity of whichever moon you'd like to use—meaning the moon's velocity relative to Saturn—since a perfectly tethered object would, of course, attain the same velocity relative to Saturn as the body towing it. If the former, then you need to find the moon's escape velocity—i.e., the minimum speed an object must achieve to escape the surface and enter an orbit around that moon— There are probably orbital velocities listed for most or all of Saturn's moons... somewhere. And keep in mind that the easiest orbital tether is going to be one with the "space end" in geosynchronous (lunosynchronous? selenosynchronous?) orbit, so that is probably the number you want. Evan (talk|contribs) 16:29, 20 August 2014 (UTC)
The only reason I can see to "tow" something "around the rings" is if you want it to move at a speed different from that of the ring particles (without constantly expending reaction mass), so I'm guessing you mean to hang your vehicle from a body in higher orbit? So you want to divide the circumference of a ring orbit (2π× the radius of some circle in the ring) by the period of whichever moon you use as the anchor, and that gives you the speed. —Tamfang (talk) 01:17, 21 August 2014 (UTC)
I'm not too sure about the antecedents, but this does seem like a clever use of a space elevator, or really, a space tether. Because the gravity of Saturn's moons is so small, very little tensile strength is needed for a short distance - of course, if you're laying 500,000 km of cable from Rhea (moon) to somewhere deep in the atmosphere of Saturn, then no standard-issue nanocarbon space elevator cable would be sufficient. But if you're just looking to hang off some shepherd moon and scoop up chunks of ice out of the rings for whatever purpose you have in mind (batting practice???), my guess is you can do it with plain steel. (Though I'm too lazy to work the math) The advantage of using a moon is that you don't need to worry about a counterweight; the moon is so heavy that its equilibrium will be little altered by the hanging cable. Wnt (talk) 22:23, 21 August 2014 (UTC)
The orbital speeds of Saturn's moons can be calculated from the table in Moons_of_Saturn#Sizes. Multiply the orbital radius by 2*Pi, then divide by the orbital period to get the speed in kilometers/day. (Multiply the result by 24 to get kilometers/hour).--Wikimedes (talk) 08:23, 22 August 2014 (UTC)

Can a shooting cause gradual brain death?[edit]

Hello. In a script I'm writing, a character is mortally wounded by gunfire. After a protracted period, the character suffers brain death. Is this plausible? I've read some articles on the subject and I'm not entirely sure how a bullet wound would lead to slow brain death. (talk) 05:36, 20 August 2014 (UTC)

Your question is misleading. If a human is suffering from a gunshot wound. The human will suffer from a slow brain death while they are also suffering from a slow liver death and a slow death for every part of their body. The blood system in a human body is for all parts of the human organ. So technically yes, the character will suffer a slow brain death. (talk) 05:59, 20 August 2014 (UTC)

Thank you for the response. I've been doing mental gymnastics trying to figure out how a person's brain would die slowly from indirect bullet wounds a la drowning, while idiotically overlooking the fact that the whole body would slowly succumb from such an injury. (talk) 06:28, 20 August 2014 (UTC)

In general terms, this would be the basis for the notion of charging Hinkley with murder 34 years after the fact. ←Baseball Bugs What's up, Doc? carrots→ 08:59, 20 August 2014 (UTC)
Presumably you mean not Olaf "Braindead" Hinkley the lead guitarist of Norwegian CyberPunk-Polka fusion band "Real Asset" that disbanded in 1979 but this Hinkley. If you propose a test case to try the contention that every "attempted" murder must in the natural order of things eventually succeed, the defence will likely point to the extenuating circumstance that so-called murder victims are all biochemically pre-programmed to die anyway. Observation of Brain death can lead to a false positive test on a patient that may recover with more time. Zack Dunlap in 2008 had a false positive of this type, likely due to temporary Cerebral edema. Such events feed the fear of being buried alive that has troubled humankind for centuries. Plato wrote in "The Republic" in 380 B.C., about an Armenian soldier who was revived two days after being pronounced dead. Fear turned to frenzy in the 19th century, when wrongful burial inventions were marketed with some success. The Safety coffin was a casket with a bell attached by a piece of string which might be pulled to alert people that the buried person was in fact alive (but it is not true that this is the origin of the phrase "saved by the bell"). However if the internee really is dead, his rest in peace or maybe pieces could be assured by a US patent in 1881 on deterring grave robbers by exploding shells that fit onto a coffin. (talk) 12:00, 20 August 2014 (UTC)
And I remember when the exploding whale video was the coolest thing. One slip-up with the arming mechanism and that would be a funeral to remember! Wnt (talk) 12:04, 20 August 2014 (UTC)
  • Although of course it's true, as others have pointed out, that a wound to any part of the body can eventually lead to general system failure which causes brain death, it's also quite possible for an injury directly to the brain to cause brain death after a protracted period -- days, weeks, months, or even years. The main causes of delayed brain death are (1) the initial injury causes swelling of the brain, which gradually crushes other parts, or (2) the initial injury causes an infection inside the brain. It can also happen that the initial injury causes a blood clot that eventually breaks loose, causing a stroke. Or you can get a subdural hematoma. Looie496 (talk) 13:59, 20 August 2014 (UTC)
According to our article Mortal wound, "A mortal wound is a very severe and serious injury ...... which leads directly to the death of the victim. Death need not be instantaneous, but follows soon after." Based on this, a wound that results in a slow lingering death would not usually be called a "mortal wound". CBHA (talk) 14:13, 20 August 2014 (UTC)

Question my nephew asked me to pass on[edit]

Eight ingots of pure sodium walk into a bar. The juke-box immediately starts playing this music. Why? --Shirt58 (talk) 12:27, 20 August 2014 (UTC)

The Batman Theme's lyrics are "nananananananana BATMAN". Na is the atomic symbol for sodium. --Jayron32 12:41, 20 August 2014 (UTC)
And as they begin to leave the establishment, someone could play Na Na Hey Hey Goodbye. ←Baseball Bugs What's up, Doc? carrots→ 13:07, 20 August 2014 (UTC)
Naa na na nana na naa, nana na naa, Hey Jude ... Gandalf61 (talk) 13:22, 20 August 2014 (UTC)
Presumably these songs fall within the genre of Light Metal. {The poster formerly known as} (talk) 13:24, 20 August 2014 (UTC)
Wrong answer! That light pop act from the 1980's "BaNaNaRaMA" are by definition an admixture of light and heavy metals. Or something like along those lines.--Shirt58 (talk) 13:56, 20 August 2014 (UTC)
Vic Bondi's band opened for them. DMacks (talk) 14:23, 20 August 2014 (UTC)

Plastics oxidation[edit]

Did the plastics had been oxidation by water?--Alex Sazonov (talk) 14:01, 20 August 2014 (UTC)

There is no common plastic that reacts with water. But see the article on Biodegradable plastic. For example, aliphatic polyesters are biodegradable due to their potentially hydrolysable ester bonds. (talk) 18:27, 20 August 2014 (UTC)
Is it the paradox that, the water which is the simple chemical substance is reacted with complex (implex) chemical substances as plastics?--Alex Sazonov (talk) 16:37, 21 August 2014 (UTC)
I know that, only simple chemical substances always are reacted with simple chemical substances and only complex (implex) chemical substances always are reacted with complex (implex) chemical substances, is it right?--Alex Sazonov (talk) 17:52, 21 August 2014 (UTC)
I know that, a water always had the simple chemical valence.--Alex Sazonov (talk) 19:56, 21 August 2014 (UTC)
I know that, the chemical substances which had a simple valence are not reacted with chemical substances which had a complex valence. Valence of chemical substances is identified a statics or dynamics of charge?--Alex Sazonov (talk) 11:09, 22 August 2014 (UTC)
There is absolutely no reason why simple and complex molecules (whatever you might choose to mean by these) cannot react. Valence is a property of (oxidation states) of atoms or ions, not of molecules, so I don't understand your last two questions. --ColinFine (talk) 13:45, 22 August 2014 (UTC)
Does the properties of charge don’t prevents the chemical reactions between chemical substances which had a complex and simple valence? What does a valence of chemical substances is identifies a statics or dynamics of charge?--Alex Sazonov (talk) 15:29, 22 August 2014 (UTC)

Opera singer vs bulletproof glass[edit]

This question was inspired by X-Men: Days of Future Past, in which one character is breaking another character out of a glass-and-plastic prison. I am aware that superhero movies are rarely reliable sources for how real-world physical laws behave, but I'm curious about the general principle behind the first character's method of pulling off the jailbreak: Since in the story his mutant power is the ability to move at very, very high speeds, what he essentially does is press both of his hands to the pane of bulletproof glass separating him from the imprisoned character and vibrate his hands at a high rate of speed. The glass, of course, shatters.

It seems to me that the filmmakers intend for this method to work on the same physical principle by which opera singers are capable (under certain circumstances) of shattering wine glasses. The two main problems I see with this idea are, 1) Unlike wine glasses, bulletproof glass is not hollow and thus does not resonate as much as a wine glass, and 2) Bulletproof glass is... well, bulletproof, at least in theory. It ought to be much harder to break it than your average wine glass using only sound, and the amplitude required to do so would probably be great enough that it would be very hard to contain the damage to the glass alone. While I don't doubt that you could construct a sonic cannon of some kind that could break bulletproof glass, I wonder what difficulties there would be in doing so without destroying just about everything else in the surrounding area, including human (or mutant) eardrums. Evan (talk|contribs) 15:43, 20 August 2014 (UTC)

Presumably the destructive power applied by contact is ultrasound. In established Ultrasonic welding of plastics, high frequency low amplitude vibration is used to create heat by way of friction between the materials to be joined. Increasing the sound power to the liquefied plastic could cause Cavitation as employed in ultrasonic cleaning baths, which can erode holes in a metal foil. Crazing (sudden formation of a network of cracks) can be triggered in some glassy polymers, which offers interesting Special effect possibilities in filming. Humans exposed to ultrasound will not necessarily hear the inaudible vibrations, although it is possible to generate audible sound frequencies by mixing of ultrasonic frequencies in body tissue, but they are vulnerable to cavitation damage that may cause nausea, headache, tinnitus, pain, dizziness, and fatigue. See the article Sonic weapon. (talk) 18:10, 20 August 2014 (UTC)
Bullet RESISTANT glass is a laminate made up of thick glass panes and/or polycarbonates/laminates. The very design makes it impossible to fully shatter via sound or direct vibrations. Justin15w (talk) 15:40, 21 August 2014 (UTC)
Agreed. Only very hard items are subject to shattering due to vibration, because they can't move much. Sandwiching in softer materials allows them to squish around and absorb vibrations and change them to heat. So, melting is more likely than shattering.
Note that a similar medieval technique was to combine wooden fortress defense walls with layers of sand, which would absorb impacts. (Quartz sand, ironically, is glass, so is quite hard, but the spaces between the grains allow it to move to absorb impacts or vibrations.) StuRat (talk) 16:19, 21 August 2014 (UTC)
You should be able to break it in theory. Shattering is another story. I don't know if ultrasonoic is all that destructive, but Quicksilver should presumably find the resonant frequency of the plane of glass, which can be very destructive. --Wirbelwind(ヴィルヴェルヴィント) 23:42, 21 August 2014 (UTC)
Did the movie actually indicate the glass was bulletproof? I don't recall that it did, though I certainly could have missed it. My impression was that it was simply a thick layer of ordinary glass (which of course could shatter). Though to be fair, I may have formed that impression simply because Quicksilver shattered the glass and I already knew that bulletproof glass would never break that way. Dragons flight (talk) 00:47, 22 August 2014 (UTC)
If I'm reading correctly, true Bulletproof glass is a combination of different kinds of glass as well as polymers. It's vaguely like a transparent equivalent of plywood. ←Baseball Bugs What's up, Doc? carrots→ 04:05, 22 August 2014 (UTC)

Feral estrildid-like finches-- ID needed[edit]

I just saw these odd little birds at a local park; they seem to be some type of estrildid finch, possibly a domestic breed. I assume they are cage escapees because no estrildids are native to my area, though some have been reported (I have recently seen a Zebra Finch myself). Photos are at the bottom of my eBird checklist: (talk) 16:40, 20 August 2014 (UTC)

Are all the photos of the same bird? Anyway, small chance it could be a society finch, they are basically the domesticated version of the zebra finch White-rumped_munia. However, their coloration patterns are highly variable (do some google image searches), so I don't think you could confirm it as a society finches without catching one... Society finch is also a parsimonious answer, as they are commonly kept as pets. While some people do keep e.g. Gouldian_finches or Red-cheeked_cordon-bleu, the Society and Zebra finches are far more common outside their native ranges. SemanticMantis (talk) 22:14, 20 August 2014 (UTC)
Those are two different birds, but they looked identical. Society finches look plausible, except I don't see any on Google with orange beaks. I might also note that there have been some odd sightings of orange-cheeked waxbills and bronze mannikins around here, but neither of those seem likely. (talk) 22:24, 20 August 2014 (UTC)
Yeah, the orange/red color on the beak made me suspicious too. The only other guess I have is female or juvenile strawberry finch aka Red_avadavat, though again, they have a lot of variation in color, especially on the pet market where many birds are not purely wild type. Actually, come to think of it males probably wouldn't be in full color this time of year, assuming you are in North America. I'm fairly sure society finches can and will breed with other estrildids, especially if if a conspecific mate for the wild type is lacking (they are much easier to breed than wild types, and are often used as living incubators for other species). So, a hybrid (e.g. society and zebra) might be an option too. Looking through Estrildid_finch I only see a handful that I've ever heard of for sale on the pet market (my mom used to breed finches, so I heard a lot about that market...) Of course it might not even be an estrildid, but I agree with you that that's what these unknowns look like, based on size, body shape, and beak shape. That's about all I've got, good luck! SemanticMantis (talk) 00:03, 21 August 2014 (UTC)
Juvenile avadavats do seem like the most plausible option I've investigated so far. I have also wondered if their two-tone beaks are in a transitional stage, from juvenile to adult or nonbreeding to breeding. (talk) 00:13, 21 August 2014 (UTC)

OP here: I have talked to a local birder who saw my eBird post, and it seems my birds are not estrildids at all. They are juvenile Pin-tailed Whydahs, which look like estrildids because they are both related to, and brood parasites of, birds in that group. So can I get this marked as resolved? (talk) 18:47, 21 August 2014 (UTC)

Interesting! I can't find many good photos of juveniles, but I'm willing to trust the judgement over a local birder over my own armchair guesses :) FYI, you can mark any of your own questions as resolved whenever you like, using the {{resolved}} tag, which I will do now below. Cheers, SemanticMantis (talk) 21:27, 21 August 2014 (UTC)

August 21[edit]

Hydrocolloid techology (plaster)[edit]

Please check if the chemistry behind Compeed plaster is properly described in Techology part. I was using sources like patents, Compeed description at Expainthatstuff article]) as well as Amazon ingredients data. -- TigerInWoods — Preceding undated comment added 03:33, 21 August 2014 (UTC)

Explosive gel/foam[edit]

In some video games, like Batman Arkham Asylum, they have a gel or foam that comes out of an aerosol can that you can use to blow stuff up. Does something like this exist IRL? (talk) 03:37, 21 August 2014 (UTC)

You can buy aerosol cans of shaving foam and Polystyrene foam (Styrofoam). The latter solidifies and is useful for filling cavities in house walls and lifeboats, is ubiquitous in litter such as packing peanuts and disposable coffee cups, but is hardly explosive enough to impress the batty rogues of Gotham City. (talk) 13:48, 21 August 2014 (UTC)
Does the foam go out an explode on its own, or is it more like spray the foam, then ignite to start an explosion? For instance, If you were to take a can of the spray Polystyrene mentioned above, and mix it with gasoline, you'd get a version of napalm. Not really explosive, but I can see Batman spraying napalm on a bad guy then throwing a match to light it. Vaguely similar real-world weapons are the Greek_Fire and Flame_fougasse, but they are both more firey than explosive. SemanticMantis (talk) 14:34, 21 August 2014 (UTC)
Well, if you could get the foam to have the right ratio of oxygen and fuel, and little else, you might be able to create a sort of thermobaric weapon, although this one would have it's own 100% oxygen inside the bubbles, and not rely on atmospheric oxygen. The bubble material would be the fuel. I suspect you'd get more of an explosion this way than if the foam was all fuel and needed oxygen from the air. That would only burn at the edges, not explode, since air is only 21% oxygen. StuRat (talk) 16:27, 21 August 2014 (UTC)
While not foamy, C-4 is malleable. I always assumed Batman used something a little more advanced, but similar. --Wirbelwind(ヴィルヴェルヴィント) 23:28, 21 August 2014 (UTC)
I wonder what would the effect would be of mixing RDX with a polyurethane spray foam? Plasmic Physics (talk) 01:15, 22 August 2014 (UTC) (talk) 12:27, 22 August 2014 (UTC)

August 22[edit]

MO diagrams and term symbols[edit]

Regarding multiplicity, does the orbital momentum of unpaired electrons in non-degenerate orbitals cancel? For instance, in the hypothetical d8 excited complex, does the orbital momentum of the lone electron in the eg orbital cancel that of the electron in the t2g (is it a singlet or a triplet)?

↑↓  ↑↓  ↑

Plasmic Physics (talk) 12:12, 22 August 2014 (UTC)

Multiplicity (chemistry) is solely about the number of unpaired electrons, not about their energy levels. The change (or lack of change) in total spin is one of the selection rules for electronic transitions. See Fluorescence#Physical principles for more discussion. DMacks (talk) 20:15, 22 August 2014 (UTC)
So, singlet then? Plasmic Physics (talk) 21:17, 22 August 2014 (UTC)

Solid state flight[edit]

Is it possible to propel a vehicle that flies in normal Earth atmosphere by some means that does not involve macroscopically moving parts?

  • There is a very crude device the Crookes radiometer that does so weakly in a thin atmosphere, but I am thinking there ought to be some way to greatly improve its power. I understand you can't have a Maxwell's demon, but could you have a flat sheet of metal that somehow acts on air molecules that bump up against it so that those moving straight out bounce elastically, those that bounce to the left are greatly accelerated, and those that bounce to the right lose most of their energy, using only a catalytic amount of energy equivalent to not much more than those air molecules will generate when they eventually smack into others and reach equilibrium?
  • How about an electrostatic system that charges tiny regions of air along a flat plate, then pushes on them with carefully patterned charge on the plate that responds adaptively to the measured external charge and pressure patterns?
  • Or a gel that holds large amounts of dissolved air, releasing it on one side and absorbing it on the other to provide lift?

Etcetera. Could anything like this work? (But please let's exclude space-based solutions like photon drives, magnetic sails, etc., and any ordinary sort of hot air balloon) Wnt (talk) 12:41, 22 August 2014 (UTC)

Ramjets and solid fuel rockets have no moving parts - at least, on paper. In practice, real aircraft and rockets have electric pumps, hydraulic valves, starter devices, control surfaces and all sorts of peripheral moving parts. Nimur (talk) 14:15, 22 August 2014 (UTC)
Those without an irrational aversion to nuclear-powered aircraft may wish to consider nuclear ramjets such as Project Pluto. -- ToE 14:31, 22 August 2014 (UTC)
That prototype looks suspiciously like the rocket used in Flesh Gordon. ←Baseball Bugs What's up, Doc? carrots→ 15:30, 22 August 2014 (UTC)
Well, you need an upward force to counteract what exerts a force?
  • Bouyancy - so you have to displace the air with something lighter - which basically means balloons. Hot air, hydrogen, helium, methane...a vacuum (which is tougher than you'd think!).
  • Action/Reaction - Newton's third law lets us push something downwards and have our aircraft go upwards as a result. The 'something' can be the air - or something that's ejected from the aircraft itself.
    • If it's the air itself, then you're thinking about jets and wings. But to use a wing, you need forward speed - which means either needing a rotor (like a helicopter or a hovercraft) - which fails the "no moving parts" rule - or something that uses a wing, needing a horizontal thrust instead. Generating horizontal thrust without moving parts is more or less the same problem as generating it vertically...although a glider operates without an onboard power source. Jets are definitely possible. RamJets...or pulse jets...or scramjets. The only moving parts are the fuel itself.
    • If it's something carried aboard the aircraft, then you have a rocket - or something very like one (eg that crazy spacecraft that drops atom bombs behind itself and then explodes them!) Firework rockets have no moving that could do water rockets and such like. Of course if you count movement of the fuel as a "moving part" - then rockets are out of the question.
    • You could imagine an aircraft with a massive laser beam aiming downwards that would gain lift by photon pressure! (Well, you could *imagine* it...I don't think you could actually make it work!)
  • Electric/magnetic forces - So we can think of a linear-induction motor powering a levitating train. Those can certainly be built with no moving parts. Trouble is that the magnetic force decreases as the square of the distance - so flying more than a few inches above the ground will be difficult!
  • Forces exerted by something fired up from the ground, rather than down from the aircraft. So you could imagine a ground vehicle or some kind of a track or chamber which is generating an enormous column of upward moving air on which the craft balances. Those "indoor sky-diving" facilities use an enormous fan to blow air upwards and turn people into unpowered "aircraft"...if you're prepared to not count the thing that remains on the ground as a part of the aircraft - then there are all manner of ways to think of doing this. In a sense, a long distance glider that uses thermals and slope lift to get where it's going is using power generated elsewhere to do the work. You could imagine a large array of cannons on the ground, firing heavy weights upwards to impact the underside of a heavily armored plate that could be kept in the air that way. Basically, any mass, propelled upwards from the ground, could support the craft...if you allow the moving parts on the ground-based component to not count in the "no moving parts" rule.
I'm sure there are other possibilities.
SteveBaker (talk) 15:55, 22 August 2014 (UTC)
Ionocraft Jim.henderson (talk) 16:06, 22 August 2014 (UTC)
This is the general idea I was picturing: airflow would presumably be right to left. No idea if this could work.
The ionocraft is indeed an interesting lead! [10] I was reaching toward something similar in the second point above, but what surprises me about the hobbyist ionocrafts is that they rely on having single, fixed positive and negative electrodes. I would think that you could pattern the charge on a flight surface so that you would first use a very strong positive and negative voltage and intentional discharge to create little puffs of positive and negative air along its length, then continuously charge ever-changing strips of the surface to be intensely negative just behind the positive puff and vice versa so that they would always be pulling the surface forward relative to the puffs in the air, but without an actual discharge that would cancel the puff out. Wnt (talk) 17:10, 22 August 2014 (UTC)
If you're willing to put in a very large amount of energy, you can do nearly anything! The trick is to make this technology competitive with the costs, safety, and reliability, that can be delivered by more conventional propulsion schemes. Nimur (talk) 17:26, 22 August 2014 (UTC)
Well, the ionocraft article claims the method is very efficient, but doesn't scale. I don't know what would happen if it could scale, and I'm not sure this would really be a way to get there, but I feel as if there ought to be a way... Wnt (talk) 17:52, 22 August 2014 (UTC)

What do you think the cushion is made of?[edit]

Rattan chair.jpg

Thx. Ben-Natan (talk) 13:11, 22 August 2014 (UTC)

Waffle fabric? --Jayron32 13:46, 22 August 2014 (UTC)
I ask myself if there is any Leather in it?, Or how high are the chances it's filled with feathers or wool? Ben-Natan (talk) 14:00, 22 August 2014 (UTC)
This is really into speculation territory, but seems harmless. I assume you can't physically examine the object, or then you probably wouldn't need to ask. Anyway, I see no indication of leather. It is possible some old rattan and wicker work might use leather for lashing, but it is not common in my experience, and leather is much more expensive and less durable than other options (synthetics, integral woven wicker, etc.) I suspect the odds of wool or down stuffing to be very low. Cushion indicates a variety of stuffings, but most stuff made in the past ~40 years will have synthetic stuffing or perhaps cotton batting. The simple reason is that synthetics are much cheaper, and last longer, even if they don't feel quite as nice. Wool and feathers can both be allergenic, which is another reason to avoid them. I'd only expect to see wool or feathers in rather expensive furniture, which this does not seem to be (I do like the chair, it just doesn't seem like an expensive model to me :) SemanticMantis (talk) 17:21, 22 August 2014 (UTC)
As long as we're speculating, my first thought, given the cushion's thinness and lack of lumpiness, was foam rubber. Deor (talk) 20:02, 22 August 2014 (UTC)

What is a phone number?[edit]

A person can move elsewhere in the same town and take his or her landline phone number along instead of changing it, or even change it to a cell phone number. Or if that person is being harassed, he or she can change landline phone numbers. Or different people in the same house can have different landline phone numbers. I thought I had the answer to this question when I discovered the concept of IP address. But several branches of the same library system and several hotels in the same resort community have the same IP address when I try to edit Wikipedia without signing in. Plus AOL has dynamic IP addresses. And apparently unlike me, most people get their Internet service through the cable company. So there must be something comparable to an IP address that the phone company uses to identify you.— Vchimpanzee • talk • contributions • 18:10, 22 August 2014 (UTC)

Well, this question becomes a lot simpler if you consider common phone systems from e.g. 1980 or so. The reason being, Telephony services and IP phones now underlie even basic "land line" services in many areas, so in some cases there aren't that many distinctions between phone service and internet service. This is especially true for things like businesses, universities, hotels, etc., as it is now often less expensive to use the internet for calls in situations where you want a lot of phones in a relative small spaces. For the historical perspective, see Telephone_exchange, Public_switched_telephone_network, Telephone_numbering_plan, and even Telephone number. So, today the line between "phone number" and internet services is very blurry, but in the past, the phone systems basically worked via phone companies assigning numbers to customers, and using manual or digital switch devices to route calls. The key distinction is that the old phone networks had fixed cables, and calls had to travel down certain paths to be connected. With modern Packet switching (e.g. the TCP/IP that supports the internet), any given packet might take a different path between host and client. (I think I got most of the basics here right, but of course welcome clarification or correction if necessary) SemanticMantis (talk) 19:35, 22 August 2014 (UTC)
I guess what I'm trying to accomplish is something like what cops do in movies or TV shows. Thanks for trying.— Vchimpanzee • talk • contributions • 20:31, 22 August 2014 (UTC)
You mean like a call tracing or Telephone tapping or something? Cops do lots of things on tv, not sure what you might be thinking of. If you're interested in the kinds of shenanigans people can get up to with phones, you might be interested in phreaking. Again, it was a lot different in the past, I don't think whistling into the phone will get you free calls these days :) SemanticMantis (talk) 20:42, 22 August 2014 (UTC)
  • For cell phones, each phone has a unique identification key entered on its SIM card, which the phone company uses to identify that phone and look up its subscriber information (including phone number) in a database. For landline phones I don't think there is any such universal system -- each phone company is allowed to implement the mapping from phone number to physical signal route in any way it wants to. Looie496 (talk) 21:12, 22 August 2014 (UTC)
To quibble for the sake of it, the IMEI is stored on the phone itself. The unique number on the SIM is the IMSI. Tevildo (talk) 21:22, 22 August 2014 (UTC)