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January 28

Does an undampened magnetic spring system ever stop?

If a magnetic spring system, like this one[1], is placed in perfect vacuum and the center rod is replaced with a magnetic equivalent so there's zero fiction, will the system ever stop after an initial excitation? I know for the traditional spring system the energy will slowly be converted into heat and it will eventually stop. Does the magnetic system also convert some of the kinetic energy into heat? WinterWall (talk) 07:52, 28 January 2015 (UTC)[reply]

Yes, subjecting a material affected by magnetism to a variable magnetic field will generate heat. StuRat (talk) 07:59, 28 January 2015 (UTC)[reply]

Doh! We even have an article on it: magnetic damping. Thanks for the help, and sorry for not searching hard enough beforehand. WinterWall (talk) 08:10, 28 January 2015 (UTC)[reply]

Resolved

Flower ID

Can someone please identify the flower ID please? Nikhil (talk) 16:23, 28 January 2015 (UTC)[reply]

Where did you see it?--Shantavira|^{feed me} 16:54, 28 January 2015 (UTC)[reply]

Yes more info would help. If you took the photo, not only where, but when? Looks a bit like a partridge pea to me. The things to check that can make you more sure (or rule this guess out) 1) Does the flower have bilateral symmetry? All legumes do, if this one doesn't it's not a partridge pea. Complicating the matter is that partridge pea flowers look a bit like radial symmetry at a glance, but one petal should be bigger than the rest, with 5 total. 2) Do the seeds have a pea pod shape? That plant might not have set seeds yet, but (assuming you took the photo) you could check back in a few weeks. Browse through this image search [2]] for more images. SemanticMantis (talk) 17:14, 28 January 2015 (UTC)[reply]

I strongly suspect it's an Acacia of some sort, the leaves and thorns indicate this, and they usually have yellow flowers. But there are on the order of 1,000 species. μηδείς (talk) 22:01, 28 January 2015 (UTC)[reply]

You know I wasn't sure if there were thorns or not. Looking more closely... I'm still not sure :) Looks a bit too sturdy for Partridge Pea though, and the leaves look sclerophyllic, which also points toward Acacia. Of course neither of these genera are native to India (of which OP is a citizen), but they could probably grow there. Anyway, we both came up with guesses in the Fabaceae family, so that's something. At the very least, the same things that I mentioned would rule out Partridge pea would also rule out Acacia spp., but we'd probably need a key and a sample to get to get positive confirmation on species level ID. SemanticMantis (talk) 22:46, 28 January 2015 (UTC)[reply]

The leaves make me think of Caesalpinia. Richard Avery (talk) 08:19, 29 January 2015 (UTC)[reply]

What I thought were thorns may be bare twigs. In any case it's obviously in the Fabaceae. μηδείς (talk) 17:49, 29 January 2015 (UTC)[reply]

Chirality

Maybe I don't completely understand chirality, but the sentence "no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide" in chirality (chemistry) looks wrong. Due to symmetry in biology the human body is an achiral object - if you align both palms for applause or prayer, for instance, then both palms will coincide (as both halves of the body do). And if you lean your palm against the mirror, the reflection will match it. What's wrong actually? Brandmeister^talk 17:53, 28 January 2015 (UTC)[reply]

What they mean is you get the mirror image. A right hand glove and a left hand glove are never exactly the same, no matter how you rotate them. They are mirror images, instead. Try putting the glove on the wrong hand to see what I mean.

Now I agree that the word "coincide" doesn't quite convey what they are trying to say, as we might very well say "the major features in the mirror image coincide with the original". But that's a problem with the language, which lacks a simple, universally understood word which means "chirality". StuRat (talk) 18:19, 28 January 2015 (UTC)[reply]

Chirality and handedness are synonyms, its usage of which should be clear when used in context (so as to not be confused with hand preference). -Modocc (talk) 19:01, 28 January 2015 (UTC)[reply]

The two palms coincide, but the two hands do not. Starting at a coincident point on the palm, to get to the knuckle of one hand you have to go in a different direction than the knuckle of the other hand. There's no way you can orient your hands such that all parts (front, back; top, bottom) will simultaneously align. (Palms, when treated as 2D objects like you do here, aren't chiral. In fact, no 2D object is chiral in 3D space.) Likewise, when you talk about humans being symmetric and achiral, that's for the human as taken as a whole. When you talk about hands as distinct objects, they are not chiral. You can get an achiral object from the combination of chiral sub-parts, if you attach the two mirror images across the plane of symmetry. You see this in chemistry, too, where they're called meso compounds - there you have molecules which have individual carbon atoms which have chirality, but are organized in such a way which the molecule as a whole is achiral, a fact which can be confirmed by optical rotation. One problem you may be having is a difficulty in envisioning "coinciding" hands, because of the physical impossibility of actually doing it. Perhaps a better phrasing is to talk about being able to move from one to the other by just translation - or equivalently, the fact that there exists an orientation of the two objects where they can be lined up side-by-side with all corresponding points placed exactly the same distance apart. So for your folded hands, this doesn't work as the palms are touching but the knuckles are 2-3 cm apart. Likewise with half a human body, you may get the tips of the nose to coincide, but the shoulders are then half a meter apart. As long as you account for their non-zero thickness, there's no way to line your hands up side-by-side such that all corresponding points are an equivalent distance apart. -- 160.129.138.186 (talk) 20:11, 28 January 2015 (UTC)[reply]

What causes electromagnetic induction?

I get that the Faraday's law of induction explains what will happen when a magnetic field interacts with an electrical current, but what is the cause of the electromagnetic induction? Couldn't the current flow in the opposite direction? --Noopolo (talk) 17:56, 28 January 2015 (UTC)[reply]

Magnetic induction is a fundamental behavior of the universe. We can write lots of mathematics to describe it, but all those equations are just quantitative descriptions of a thing that we see: a change in an electric field causes a corresponding change in a magnetic field. The fact that there is a specific direction is not something we can presently explain - although we can describe it in very great detail. You can read more about this concept at our article: fundamental interaction. If you spend many years studying physics, you can learn how to describe these interactions at many layers of abstraction and at various levels of detail. Nimur (talk) 18:09, 28 January 2015 (UTC)[reply]

The right hand rule is so due to the conventions by which people chose + and - for E and B. There's nothing intrinsically positive about positive (sometimes people complain that positive electric fields really ought to be where the electrons are... but really there's no intrinsic reason why the smaller particle should be positive either, so yes, it's arbitrary) Wnt (talk) 21:59, 28 January 2015 (UTC)[reply]

I didn't mean why it is represented the way it is, was rather asking about what Nimur explained above.--Noopolo (talk) 00:17, 29 January 2015 (UTC)[reply]

How Strong is the Force Which Drives Hubble Flow?

If I have a small solid object, a coin say, is it expanding with the Universe by an incredibly small amount, or actually by zero? What about if I had a very long pièce of string running to a planet in a distant galaxy? Would it be stretched by Hubble flow? 2A01:E34:EF5E:4640:E19D:C1C5:D0B3:F799 (talk) 18:14, 28 January 2015 (UTC)[reply]

Do not worry coins do not expand. Ruslik_Zero 20:32, 28 January 2015 (UTC)[reply]

At least, not yet... Wnt (talk) 21:55, 28 January 2015 (UTC)[reply]

The hubble flow is relative momentum, not a force. If two objects are moving away from each other, they'll continue to move away unless acted on by some force, such as gravitation (attractive) or the cosmological constant (repulsive). If your coin or string is expanding, it'll continue to expand until something stops it. In the case of the coin or the string it's the electromagnetic binding between the atoms that will stop the expansion, almost immediately in the case of the coin and pretty quickly in the case of the string. If the coin or string is not expanding or contracting, it won't spontaneously start to do so. -- BenRG (talk) 01:41, 29 January 2015 (UTC)[reply]

To reiterate and restate what BenRG has already stated: Hubble Flow (and by extension the metric expansion of space) is not caused by some unknown force currently acting on objects, it is the motion imparted on objects by the Big Bang which has not yet been counteracted by other forces. We know from Newton's first law that objects will not change their relative velocity unless an outside force acts on them. For any sufficiently close objects, from individual galaxies down to you and I, down to individual atoms, there are the four fundamental forces which have long since "canceled out" the effect of the initial motion imparted on them from the Big Bang. However, for sufficiently distance objects, there are not enough forces between the objects to slow them down from their initial push given by the big bang. They're just continuing to drift apart without any additional forces, as the initial "push" they got from the Big Bang has not yet been counteracted by other forces. In simple terms: Hubble Flow represents inertial motion originally imparted by the Big Bang, and is not "caused" by any further forces. --Jayron 32 03:13, 29 January 2015 (UTC)[reply]

Hubble Flow is just inertia, got it. Are you oversimplifying with your 'forces cancel out' or am I just being naïve when I think that add up all the forces and divide by the mass to get an ever decreasing acceleration and hence an, after all this time, vanishingly small but nonetheless non zero velocity? — Preceding unsigned comment added by 2A01:E34:EF5E:4640:E19D:C1C5:D0B3:F799 (talk) 06:35, 29 January 2015 (UTC)[reply]

No, there is a zero relative velocity due to Hubble flow for all sorts of things, really anything galaxy sized or smaller. For example, the you're not flying apart; the electrostatic forces keeping you together means your atoms are not affected by Hubble flow: since the big bang is no longer happening, there's no additional force to make you get bigger. The Milky Way is held together by the gravity of all of the stars in it. The individual stars are not all spreading out due to Hubble flow, the galaxy holds together all on its own by its own gravity, and since the Big Bang still isn't happening now, the Milky Way is a stable structure, it is not expanding itself. It is only when you get on the scale of things larger than galaxy clusters or bigger that you see Hubble Flow in effect. The thing that Hubble noticed (LeMaitre actually. Hubble gets more press than he probably should, but I digress) was that, not only were distant galaxies receding, they were receding faster the further away you got; in other words it appeared that they were accelerating. However, this is also not due to any force, but a complication of the speed of light: the further a galaxy is from us, the greater its speed because it has more of its initial Big Bang-imparted velocity, because we're seeing it at a time when it was closer (temporally) to the Big Bang. Galaxies that are closer to us have been acted on by the gravity of other, nearby, objects for a longer time, so have been decelerated by them. However, eventually matter will get slowed down to the point when it has literally zero velocity left over from the Big Bang. From that point forward, until forever, it will no longer be subject to Hubble Flow. --Jayron 32 10:55, 29 January 2015 (UTC)[reply]

That would be true for just inertia from the Big Bang, without an Accelerating universe. Dbfirs 11:33, 29 January 2015 (UTC)[reply]

Some of the comments above seem to ignore that the expansion is often described as countering gravity that would pull the cosmos together in a closed universe, and is described as dark energy, quintessence, cosmological constant etc. that exerts 'negative pressure' which, for reasons I still don't really comprehend, seems to mean that it pushes things apart. Wnt (talk) 12:29, 29 January 2015 (UTC)[reply]

Yes, the explanations seem to be 5 billion years out of date. Dbfirs 13:31, 29 January 2015 (UTC)[reply]

No, you need to be careful on the exact words here. By definition Hubble Flow, and the Metric Expansion of Space, is the inertial movement of matter caused by the Big Bang. There ARE other forces at work, some known about (gravity or electrostatics that holds objects together), and some which are NOT fully explained (all the one's you've mentioned). It's only been since the 1990s or so that we've noticed that the universe is expanding slightly faster than Hubble Flow would predict from the Big Bang, and we call that effect "dark energy" and "cosmological constant" because that sounds much better than "fucked if I know why it's happening", which is what both of those amount to. For the past 20 years or so, we now know (though LeMaitre and Hubble and all the rest did not) that the universe's expansion seems to be accelerating by a very real, but very small amount (the effect is so negligible, that it took that long for our measurements to produce precise enough results to notice it), which is why fudge's like "dark energy" have been introduced. But it's a total fudge: no source of "dark energy" has ever been confirmed, no one can identify what it is or how it works, "dark energy" is then just a code word for "this accelerating expansion thing we've recently noticed by can't explain". --Jayron 32 14:57, 29 January 2015 (UTC)[reply]

Yes, that's correct; the main effect started within 10⁻³² seconds after the Big Bang. I agree it's quite possible that the "acceleration thing" of the past five billion years is just some kind of illusion, but I've no idea how to explain it. Dbfirs 18:39, 29 January 2015 (UTC)[reply]

Inflation doesn't start 10⁻ⁿ seconds after the big bang. I don't know where that (very common) error originated. Inflation erases all evidence of what caused it, so there's no way to know how long it lasted, or what state the universe was in when it started, or how long the universe had already existed at that point. But it seems safe to say that the state before inflation was not big-bang-like, because the whole point of inflation is to explain the observed big-bang expansion, and it would be completely pointless if the universe was already like that before it started. -- BenRG (talk) 20:53, 29 January 2015 (UTC)[reply]

I see what you mean, but we have articles on Planck epoch, Grand unification epoch and Electroweak epoch that mention these times which refer to non-inflationary cosmology. Even Inflationary epoch uses the timescale. Would it make any more sense to say "after the theoretical singularity"? Dbfirs 21:49, 29 January 2015 (UTC)[reply]

If the accelerating expansion is really caused by a cosmological constant, then it's just another term in the gravitational force. We've never found a "cause of gravity" either, but we can still claim to understand it pretty well. In any case, the crucial thing is the difference between velocity and acceleration. Aristotle was wrong about moving objects having to be pushed to keep moving, and in a cosmological context he's still wrong. Regardless of the nature of the mysterious acceleration, it's an acceleration, not a "velocitization", and that makes it the same as gravity for this purpose. -- BenRG (talk) 20:53, 29 January 2015 (UTC)[reply]

I think I asked a similar question a few years ago. If the universe is expanding, and we are part of it, then why aren't we? If it's all relative, then there should be no perception of the universe's expansion at all. If I am sitting in a room and my TV suddenly starts to get bigger, whilst I also start to get bigger (as well as the rest of the room), then there would be no noticeable change. KägeTorä - (^影_虎) (Chin Wag) 19:33, 29 January 2015 (UTC)[reply]

Yes, I remember reading a Science Fiction story based on a changing scale (only it was shrinking). In reality, we'd have no way to detect this sort of change unless it was happening only in our region (or unless light was not affected). The whole of science is based on the assumption that this doesn't happen. Dbfirs 20:13, 29 January 2015 (UTC)[reply]

Size isn't relative. The density of metallic solids, for example, is set by physical laws. You can't make a coin twice as large with the same number of atoms of the same metals. -- BenRG (talk) 20:53, 29 January 2015 (UTC)[reply]

Well it was only a cheap science fiction story -- evidently more fantasy than science since the necessary change in physical constants would presumably have been detectable and would have resulted in different scale changes for different materials. Dbfirs 21:49, 29 January 2015 (UTC)[reply]

The only noticeable change I can feel is that I need glasses to see my TV (which incidentally is bigger than it was before), so it may be moving further and further away from me, but maybe that's just because I am getting old, and have a bigger TV......) :) KägeTorä - (^影_虎) (Chin Wag) 03:52, 30 January 2015 (UTC)[reply]

Isn't the only way you could detect the change is to compare the same object with itself at some other point in time or to the CMB itself?165.212.189.187 (talk) 15:47, 30 January 2015 (UTC)[reply]

List of psychological activity, paranormal or psychic phenomena:

Peeps, can you help me naming some ‘psychological activity’ (thinking, emotions, memory, desires, will…) as well as the so-called ‘paranormal’ or ‘psychic phenomena’ (extrasensory perception, out-of-body experiences…). -- (Russell.mo (talk) 21:50, 28 January 2015 (UTC))[reply]

Have you read our article Paranormal?

--TammyMoet (talk) 13:15, 29 January 2015 (UTC)[reply]

No, I have not. Thanks -- (Russell.mo (talk) 15:24, 29 January 2015 (UTC))[reply]

The article doesn't meet the requirement. -- (Russell.mo (talk) 20:45, 29 January 2015 (UTC))[reply]

I'll try to find out where I got the sentence paragraph from. -- (Russell.mo (talk) 20:48, 29 January 2015 (UTC))[reply]

Black Powder vs. Smokeless Powder

Is it true that smokeless powder has greater energy density while black powder has greater power density? Assuming this is true, if equal amounts of powder were used in a load in a firearm, would the greater power density of black powder give it the same muzzle velocity as smokeless powder? 69.121.131.137 (talk) 22:50, 28 January 2015 (UTC)[reply]

Power density is a strange way to put it, but if I read the concept correctly; power is work divided by time. So "power density" would simply be the energy released divided by the time it takes to release it, divided again by the mass of the substance (for the "density" bit. Or maybe the volume. Extrapolating from energy density). What you would want to compare is the Burn rate of smokeless powder versus black powder. This chart compares the burn rates of various propellants, but does not give raw numbers, it only "ranks" them. But what you really need to know is how fast traditional powder burns compared to whatever formulation of smokeless powder you are looking at. Also, be careful here: black powder is basically one thing, but there are dozens upon dozens of different things called "smokeless powders" and they all have different properties. So there may be no way to accurately answer your question without comparing specific powders. --Jayron 32 03:05, 29 January 2015 (UTC)[reply]

How does black powder compare to the fastest one on that list. 69.121.131.137 (talk) 03:51, 30 January 2015 (UTC)[reply]

Black powder comes in many grain sizes with different burning characteristics. Blackpowder for artillery weapons even used to be made in different grain shapes. Rmhermen (talk) 18:38, 30 January 2015 (UTC)[reply]

AEROANDTECH

Good morning, I am Morelli Luca , the designer and owner of the AEROANDTECH project; I'd like to update the information given with AEROANDTECH page, but each time that I do it, I find the day after again the wrong information. The wrong information are giving us economic problems, so, how can I fix the right information avoiding that someone will change again them?

it is very important, please answer thanks Ing. Morelli Luca — Preceding unsigned comment added by 62.18.86.170 (talk) 23:01, 28 January 2015 (UTC)[reply]

The article in question seems to be Aero & Tech Nexth. Alansplodge (talk) 01:59, 29 January 2015 (UTC)[reply]

This looks like a content dispute. The OP needs to use the article talk page to discuss it with other editors. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:06, 29 January 2015 (UTC)[reply]

Note: This was also asked on the Help desk. Dismas|^(talk) 02:07, 29 January 2015 (UTC)[reply]

You're unlikely to be happy about this but...

The thing here is that you imagine yourself (as owner/designer/whatever at the company) as being the 'authoritative' source of information - so you must be right. However that's categorically NOT how Wikipedia works. You have no more standing in writing this article than anyone else who comes here...to the contrary, actually - because you have an active interest in representing both company and product in a good light, you have an inherent conflict of interest and people are likely to view your edits with the deepest suspicion. Our WP:COI guidelines explain this in more detail.

The information that goes into the article must come from a reliable third-party source. Something that our readers can verify. We can't take your word for these things...crazy though that sounds. What you need to do is to present information that's been published in aviation journals, newspapers, places like that. That information is considered "reliable". You can read our guidelines for reliable sources at WP:RS.

This does seem very weird when you, personally, know "the truth" - but you have to consider what would happen if we allowed the owners and employees of businesses to come here and write their own articles. We'd be nothing more than an advertising platform - not a trusted encyclopedia. Because businesses would really, really like only favorable information to be in our articles about them, we simply cannot trust what they tell us directly. So we rely on journalists, book authors and people like that to do research and to provide a somewhat balanced view.

Looked at another way, you wouldn't like it if your competitor were inserting falsehoods about your company into the article either...but if we allowed people to write stuff without reliable sources, that could easily happen. Anyone can create an account here and claim to be anyone they want...they could easily claim to be an 'insider' when they aren't.

The best way to explain this is that Wikipedia editors are not supposed to come up with information themselves - they can only find it in reliable source. This is explained in our guideline about 'original research': WP:NOR.

When I was writing the article about the Mini Cooper - I wanted to write about the top speed of the car in each gear, which I knew because I'd driven my Mini on a track and measured the flat-out speed myself with GPS and a trackside radar gun. However, even though I knew the number for a fact - I had to find an automotive magazine that reviewed the car and use that as a reference. SteveBaker (talk) 03:00, 29 January 2015 (UTC)[reply]

Note that what you can do is add a link to your own website, if there isn't already one, in the "External links" section at the bottom. And on your own web site you can, of course, put as positive spin on your products as you want. StuRat (talk) 13:40, 29 January 2015 (UTC)[reply]

That link has been there since April 1012 when the article was first created...so that's clearly not enough for our OP. The latest revision of the article is heavily reliant on a single reference in the "World Directory of Leisure Aviation". From Wikipedia's perspective, that's probably a reasonable source of information...but we do refer to the manufacturers site in two other references.

In an ideal world, our OP would be telling us of a bunch of other places where the aircraft is discussed/reviewed/etc so we may broaden our base of references beyond one WP:RS and two WP:COI sources. Doubtless employees of the company would have a good knowledge of where their product had been written about. SteveBaker (talk) 19:25, 29 January 2015 (UTC)[reply]

Wow, that link has been there over a thousand years ? Impressive ! StuRat (talk) 04:13, 30 January 2015 (UTC)[reply]

It was brought from France to England by William the Concurrer. It started out as chain mail. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:44, 31 January 2015 (UTC)[reply]