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August 10

Magnetic lines of force

Why do iron fillings align themselves along the magnetic lines of force of a bar magnet, even if lines of force are imaginary? Publisher54321 (talk) 08:16, 10 August 2013 (UTC)

I believe the filings conduct the magnetic field better than the air, so this tends to cause them to clump together, aligned in the direction of the magnetic field, since the magnetic field is stronger by other iron filings than away from them. StuRat (talk) 08:37, 10 August 2013 (UTC)

Magnetic field lines talks some about it. DMacks (talk) 10:06, 10 August 2013 (UTC)

The linked section seems to do little more than mention the phenomenon. Iron filings themselves become magnetically polarized in a magnetic field – either temporarily or permanently. If an individual filing is considered, this magnetic polarization is dominant along its long axis (if it has one, i.e. is not spherical). The polarisation generates its own magnetic field, which interacts with the overall magnetic field in such a way as to orient the long axis of the filing with the field if it can rotate freely. There is no preferential positioning of a single filing though: it will simply orient itself by the field, and not move, unless there is a magnetic field gradient, in which case it will experience a small force in the direction of the increasing gradient (assuming that its polarization is allowed to align freely). The gradient is generally strongest nearest a dipole source (like a normal bar magnet). This is why the force between two magnets increases so markedly when they get very close together: this is where the gradient of the field of a magnet is highest, and the force increases with the inverse cube of the distance (if I have not misremembered it).

Each filing, being magnetically polarized, generates its own tiny dipole field, which is superimposed on the surrounding magnetic field. This creates local gradients in the magnetic field such that there are effective forces between proximate filings. A simple way to think of it is that the filings all become aligned magnets due to the external field, an then they act as you'd expect many little magnets to act: they form chains of north-to-south magnets sticking to each other. The striations formed by clustering of adjacent chains is a little trickier, but is probably attributable to irregularities in the chains that causes them to stick together, leaving gaps between clusters, thus forming the striations. — Quondum 12:30, 10 August 2013 (UTC)

To put it more completely yet more concisely: The reason the filings form spaced lines is a) as Quondom said, as each filing become magnetised by the field, it increases the local flux density attracting filings ahead and behind it in a (North-South)-(North-South)-(North-South) chain as opposite poles attract, and b) the field is thus weaker between such chains, this establishing a gradient that makes locations between chains unstable, and because like poles repel. 121.215.72.7 (talk) 13:25, 10 August 2013 (UTC)

Not entirely: the spacing instability depends on non-uniform chains. Several closely (but not necessarily exactly evenly) spaced steel wires, all in and parallel to a uniform magnetic field, will experience no forces between them. In this, there is no field gradient between the wires (although the field strength between wires is reduced compared to no wires). A filing floating between them will also experience almost no force (other than orientation). A very small residual attraction will exist for the filing to the nearest wires though: its polarization will alter the polarization in the nearest parts of the wires, which is to say, with the uniform magnetic field removed the filing will experience the same attractive force to the adjacent wires by interaction with the polarization that it induces in them as a tiny permanent magnet of the same polarization. This depends on the filing not being part of a uniform chain (like another wire). Because the chains are not uniform this is not an accurate description, but it gives a feel for the mechanisms at work. — Quondum 14:10, 10 August 2013 (UTC)

Please update Magnetic field lines to clarify/expand. DMacks (talk) 08:03, 11 August 2013 (UTC)

We know that a tangent drawn from any magnetic line of force gives the direction of magnetic field. Suppose I have a figure showing a bar magnet and direction of magnetic field around that magnet. Can I call this arrangement a vector field? I asked this question because I am not able to understand what really a vector field is. Publisher54321 (talk) 14:38, 10 August 2013 (UTC)

In physics, a vector field is a mathematical tool that lets us define a vector at every point. So, it is a function whose inputs are coordinates (x,y,z); and whose output is a vector, also expressible as coordinates (x,y,z). Usually, we put extra constraints on that function to make sure the function is continuous. And if there are any mathematicians around, we have to refine our terminology in order to be much more precise: using stricter mathematical terminology, there's a distinction between the field itself, and the convenience function that defines it. In very elementary physics, this type of abstraction is not very useful. But as you study more advanced physics, it quickly becomes important, even in the study of magnetic fields; particularly when you study transforms, geometries, and gauge abstraction.

It is worth emphasizing that solid understanding of mathematical concepts and terminology are absolutely prerequisite for studying physics. If you want to know and understand magnetic fields, you need a good understanding of the ideas of vectors, multivariable functions, and the calculus as it applies to them. If you are truly not able to understand those concepts - if you don't enjoy those concepts, and you're not the kind of person who wakes up in the middle of the night from dreaming about differentiating multivariable fields - then maybe physics is not for you.

Finally, I don't know who told you that lines of magnetic force are imaginary. They are invisible, insofar as the human eye cannot see them. But magnetic fields really are there; they do exist, they do have a force and have energy associated with them; they can do work (exerting a true force over a distance, causing physical objects to move). In the case of iron filings aligning with a magnetic field: the iron filings are arranging themselves according to the lowest energy they can get. The iron is ferromagnetic; it has a magnetic moment; so each granule interacts with the field; this can cause a torque, and can move the particle. The work to perform this motion comes from potential energy: somebody first did work against the magnetic field in order to place an iron filing in a geometric arrangement with a higher energy state. When you scatter or sprinkle iron filings, you might not be paying careful attention to how much work you're imparting to each grain: but just as you did work against gravity to lift the filings, providing energy for their motion as they fell back toward the table, you also did work against the magnet, providing the energy for them to rotate. It's a tiny amount of energy, but it's not imaginary at all. Add in some complex interactions to account for air resistance and collisions between grains, and there is so much perceivable randomness that you don't notice the work you're expending. Nimur (talk) 12:13, 11 August 2013 (UTC)

And that, friends, is what is great about this reference desk. -- Scray (talk) 13:53, 11 August 2013 (UTC)

Just a small but very important correction to the last part of Nimur's post that directly impinges on the original question by Publisher54321: While magnetic fields are most certainly real physical phenomena, lines of magnetic force are an imaginary conceptual tool that is useful in modelling or the design of magnetic devices, and are reflected in obsolete (non-metric) units. There is no texture or segregation onto lines in magnetic fields in free space or in homogenous magnetic materials - lines have no physical reality. The total magnitude of a magnetic field penetrating a given area is expressed in non-metric systems in units of lines, cf weber in SI. When showing the distribution of magnetic fields in magnetic circuits of some complexity, it is useful to draw magnetic field lines, much as it is useful to draw stream lines in a diagram of air passing over a wing for example. Doing so is not taken to imply the the air is confined to the lines. 121.221.72.86 (talk) 15:32, 11 August 2013 (UTC)

Another minor clarification: the link target in "using stricter mathematical terminology" as provided is not appropriate: the term field (as defined in mathematics) and the term field (as defined in physics) are unrelated. It is the second meaning that we are dealing with. — Quondum 16:14, 11 August 2013 (UTC)

Well, both definitions of "field" are related; it's just difficult to explain how - unless you're intimately familiar with the special mathematical language of set theory. I'm sure one of our better mathematicians could express why a scalar field (as we use in physics) is a special case of some abstract commutative ring over the set mapping R3 to R - but more to the point, they will probably have a difficult time explaining why that relationship is helpful for analysis of worldly problems. (I jab at the mathematicians in jest, but at the end of the day, I readily acknowledge that they are often more correct than the physicists). Nimur (talk) 17:45, 11 August 2013 (UTC)

Hmm. Your obfuscatory response makes me wonder about what you are trying to achieve. — Quondum 18:26, 11 August 2013 (UTC)

I guess that my point was: anybody who is qualified to understand the relationship between fields and fields is already a mathematician and already knows where to look for answers. Everybody else probably doesn't care about such details - even though the details are more correct. As physicists and engineers, we just need an occasional reminder that we're glossing over things for the sake of simplicity and succinctness. I guess that my post was a little obfuscatory for a reference desk answer. May I recommend A Transition to Advanced Mathematics - a very tiny book with very few pages-per-dollar, but still well worth the cost, for anyone who wants better answers about mathematical terminology than I could ever provide? And for everyone else, a scalar field is just a function with three inputs. Nimur (talk) 19:27, 11 August 2013 (UTC)

Unless my memory completely fails me, that they are both called "fields" is accidental and that they do not go by the same terms in every language. Would you kindly elaborate on what the connection between them is? Even if advanced/incomplete, please do. More importantly, is it that there is simply some connection between the algebraic and the geometric objects or is it a foundational connection? There's weird connections between just about every object these days, what makes this one special besides the identical names?Phoenixia1177 (talk) 08:15, 13 August 2013 (UTC)

To address the OP's second question succinctly, "Can I call this arrangement a vector field?": Yes, you can think of it as a vector field, which is how it is often treated (even mathematically, as in the vector treatment of Maxwell's equations). — Quondum 16:27, 11 August 2013 (UTC)

How many kinds of blood cells are there?

I have red in the entrey of blood cells that there are three general catgories: Red blood cells (leucocytes), White blood cells (thrombocytes) and platlets (trombocytes). I can understand from the word GENERAL that there are more kinds of blood cells, it says that there are sub-categoies of blood cells. So, how many kinds of blood cells are there in all? (In the Hebrew Wiki there are 10 kinds of blood cells: Two of them are belong to the Red blood cells, and seven of them belong to White blood cells, and one of them is a platelet. these are the kinds: 1.Erythrocytes. 2. Reticulocyte. 3. Neutrophils. 4. Eosinophils. 5. Basophils. 6. Macrophages . 7.lymphocytes . 8. Monocytes. 9. Phagocytes . 10. platlets ). So, is it correct to say that there are 10 kinds of blood cells or there are more or you have another something to say about... Thank you מוטיבציה (talk) 10:22, 10 August 2013 (UTC)

You've got things a bit confused. The usual classification is:

Red blood cells, or erythrocytes. Reticuloctes are young erythrocytes.

White blood cells, or leucocytes. There are three main classes:

Granulocytes, with three subclasses:

Neutophils

Eosinophils

Basophils, which are also called mast cells

when they leave the circulation and enter

the tissues;

Lymphocytes, consisting of three main groups:

B cells

T cells, including

Cytotoxic T cells

Helper T cells

Memory T cells

Regulatory (or suppressor) T cells

Natural killer cells

Monocytes, which are which are called

macrophages when they leave the circulation

and enter the tissues. Together, monocytes

and macrophages are refered to as phagocytes.

Platelets or thrombocytes. Not really cells strictly speaking, but rather cell fragments. We have articles on all the terms used above. Look at them for further information. Dominus Vobisdu (talk) 10:54, 10 August 2013 (UTC)

-

-

-

Well, if I understand you properly, there are 10 kinds of blood cells, here is the acount:

Red blood cells (reticulocytes are young cells)- It's one or two in the acount.

White blood cells incloud three main classes:

granulocytes with three subclasses:

1. :Neutophils. 2.Eosinophils. 3. Basophils (mast cells).It's plus three to acount.

Lymphocytes, consisting of three main groups:

B cells

T cells, including 1.Cytotoxic T cells. 2.Helper T cells. 3.Memory T cells. 4. Regulatory (or suppressor) T cells. 5. Natural killer cells.

Monocytes (macrophages/phagocytes). It's plus six to the acount.

Platlets - It's plus one to the acount.

In all, there are 10 kinds of blood cells. (I did not understand why you don't acount platlets as blood cells). Thank you for the help :) מוטיבציה (talk) 14:25, 10 August 2013 (UTC)

No. Monocytes are not under T lymphocytes. And the answer from your question ranges from three to a big bunch, depending what you mean by "kinds" of blood cells. I already explained why platelets are not cells. They are cell fragments. Dominus Vobisdu (talk) 14:34, 10 August 2013 (UTC)

I made order again in my things, and monocytes no more under lymphcytes. In regard to the platlets, I understnad your things, but I ment that I don't understand why some books and wiki itself call it "cell" (in the hebrew wiki it's called expressly: blood cell), so I wondered if what that you say is it not known to all above mentiond? מוטיבציה (talk) 15:27, 10 August 2013 (UTC)

It is a common misconception for platelets to be called cells; they are cell fragments that lack nuclei, as reflected in our article on the topic. It is appropriate to ask whether the same applies to red blood cells, but the latter are often nucleated (e.g. in infants, people with functional or anatomic asplenia, and other vertebrates) whereas platelets are not nucleated and are produced by pinching off cytoplasm from a megakaryocyte (rather than cell division). -- Scray (talk) 15:51, 10 August 2013 (UTC)

Further, it might be tempting to call anything membrane-bound in the blood a cell, but then what to call exosomes, apoptotic bodies, and enveloped viruses that might be found in the blood? Platelets are better grouped with "cells" than with "plasma", but they are even better described as cell fragments. -- Scray (talk) 15:57, 10 August 2013 (UTC)

Should we assume that the original question refers to human blood cells, or does it embrace the blood cells of all creatures having blood?

—Wavelength (talk) 16:45, 10 August 2013 (UTC)

It's pretty much the same for all vertebrates, at least as far as the main groups and subgroups of blood cells go. The last evolutionary event was the divergence of lymphocytes from monocytes, which might have occured soon after fish evolved, or perhaps soon before, so it is possible that some primitive fish like sharks and lampreys may not have lymphocytes, though I'm not sure. Basophils are perhaps an even younger derivitave of the granulocyte prototype, and whether fish have them or not is not settled. Originally, all the WBC types evolved from a phagocytic ancestor in invertebrates. Dominus Vobisdu (talk) 17:37, 10 August 2013 (UTC)

It splits further: Th0, Th1, Th2, various combinations of cytokines... no two cells are really -precisely- alike, and sooner or later, someone finds a way to distinguish them. And all the ways matter, once you understand them. Wnt (talk) 04:04, 12 August 2013 (UTC)

Main Battle Tank

My question is about Leopard 2 Tank when looking at the image in the picture of the link downward you find that part number 2 is (Main Hydraulic Pump), what is the purpose of this pump and why this pump does not exist in other tanks like M1 Abrams or T-90 -as I expect- http://imageshack.us/a/img811/4895/leopard2wieakoncpecja.png Tank Designer (talk) 11:10, 10 August 2013 (UTC)

Well, the M1 Abrams does have a hydraulic pump, but it's located in the hull rather than the turret. The main purpose of the hydraulic pump, as I understand it, is to move the turret and gun. Looie496 (talk) 14:49, 10 August 2013 (UTC)

Thank you very much but where does the pump exist in T-90 there is no where to place it-as expect only - as yo know it is very cramped from inside 86.108.126.173 (talk) 20:49, 10 August 2013 (UTC)

Actually I know hardly anything about tanks. My skills lie in the direction of knowing how to find information on the internet, not in the direction of knowing about tanks. Regards, Looie496 (talk) 15:35, 11 August 2013 (UTC)

If it isnt in the article its probably secret. --Kharon (talk) 02:07, 13 August 2013 (UTC)

on difference between serum and plasma?

I have red that the main difference between serum and plasma of the blood is coagulation factors (proteins of cougulation). Serum is without these couglations factors, and plasma is with it. Why is it needed to take out the couglation factors? what is the profit/ adventage/ use in the serume that we can not do with plasma? Thank you. מוטיבציה (talk) 14:58, 10 August 2013 (UTC)

There are many differences between serum and plasma, some of which affect laboratory assays; this is sometimes called matrix effect (a consistent effect on an assay of the matrix from which the sample is taken). Because matrix effects are hard to predict, and lab assays are developed empirically, an important principle is to stick with the matrix (specimen type, e.g. serum or plasma) for which the assay has been validated. Examples of dominant influences on assays include: (i) fibrinogen, present in high concentration in plasma but nearly absent from serum, can interfere with interactions of other proteins; and (ii) anticoagulants such as EDTA used in plasma collection but absent from serum, can interfere with assays that depend on cations like Ca²⁺. If you search for some of these things, you may find some more examples and specific references (I may do the same if others don't). -- Scray (talk) 15:24, 10 August 2013 (UTC)

• some references: review articles PMID 21400551 PMID 17377775 PMID 15915347; example 1 - differential stability in stored serum vs plasma PMID 23570966; example 2 - differential effects of heparin, citrate, and EDTA anticoagulants in plasma PMID 23473258. -- Scray (talk) 18:46, 10 August 2013 (UTC)

String bass v fretless bass guitar

What is the principal reason for the marked difference in tone between a double bass (or an electric double bass) and a fretless bass guitar? The only differences I can think of are the string thickness and length. So how do these factors affect the tone so much and cause the double bass to give a much deeper sounding richer tone?--86.177.63.179 (talk) 18:51, 10 August 2013 (UTC)

If you're comparing an acoustic double bass with an acoustic bass guitar it's because the double bass is a much bigger instrument with a larger sounding box and so it produces a deeper sound in the same way that a longer string produces a deeper note than a short one. An electric bass and an acoustic double bass can't really be compared as the sound from the electric bass is produced in an entirely different way and then manipulated electronically to give the desired sound. Richerman (talk) 22:59, 10 August 2013 (UTC)

The strings on electric basses and double basses are tuned to exactly the same pitch. So that cannot be the reason for the difference in sound. Doesnt anyone have any suggestions?--86.177.63.179 (talk) 14:28, 11 August 2013 (UTC)

Tuned to the same pitch does not mean things sound exactly the same. Richerman is right above: the size of the sound box will change the timbre. For instance, see the selection of pictures at mandolin. The round-back mandolins will sound much fuller than the flat backed ones, and so will basses with different body types. I also agree with Richerman that it makes more sense to compare within electric of acoustic groups, not between, because the method of sound production is so different. But maybe you mean to compare two basses that are identical in all aspects, except for fret/no fret? In that case, have a look at Bass_guitar#Fretted_and_fretless_basses, which describes some of the differences that come from lack of frets specifically. SemanticMantis (talk) 14:41, 11 August 2013 (UTC)

If you put the same strings on a Stradivarius and a cheap mass produced violin you will get a completely different sound - otherwise why would anyone pay millions for a Stradivarius? It's the whole instrument that produces the sound, not just the strings. Richerman (talk) 15:34, 11 August 2013 (UTC)

Yes, exactly. The frequency at which the strings vibrate will not change - but the overtones and undertones produced by all of the complicated vibrations of the rest of the instrument and the air contained in it's sounding box will be quite utterly different. Since those sounds dominate our perception of the frequency, we hear different notes. Particularly, if the string sounds (say) a middle C, the resonances through the instrument will produce a C note an entire octave down from there. On some instruments, the volume of that lower C will exceed the volume of the middle C produced by the string - and in other instruments, the middle C will be louder. Our ears would then perceive the first instrument as producing a deeper bass sound than the second. But that's a vast over-simplification - every part of the instrument vibrates - including the other strings and even the body of the musician that's playing it. The resulting vastly complex soundwave is what we hear and it's hardly related to what the string produced. Think of the string not as the object that's producing the sound - but as the stimulus that causes the remainder of the instrument to produce the sound...that's a more accurate physical description of what's happening. SteveBaker (talk) 16:53, 11 August 2013 (UTC)

Though, I would bet there are no double-blind studies comparing the tone of a Stradivarius and the tone of a reasonably-good (but not famous) instrument. Those violins command an immense price, but not only because the Stradivarius is of excellent quality. It is also a luxury good; an artificially scarce commodity whose exact scarcity is defined by brand identity (not by the actual rarity of the constituent pieces of the instrument); it is a premium price, and the higher the price, the more valuable and rare the violin becomes. Stradivarius instruments command a high price because they are expensive - a bit of ouroboros-esque logic that is also seen in the retail-pricing of diamonds and gemstones. The instrument only need be of sufficient quality to maintain its brand identity, but not to actually compete with other instruments in specific quality metrics like musical timbre and tone. With today's near-perfect machine-tools, and the cheap availability of raw materials of all sorts - in principle, we should be able to import any desired exotic wood and varnish and so forth - and we could manufacture a violin that matches Stradivarius' every detail, and sounds exactly the same in every respect; yet, we would not produce an instrument that the marketplace for antique instruments would perceive to be equally valuable.

The very same affliction strikes modern instruments: a Rickenbacker can sell for ten or a hundred times the retail price of my Peavey electric bass. The real reality of it is, nobody can tell (by listening) which brand of guitar Paul McCartney played; but because he played a Rickenbacker, it must have been the best... Nimur (talk) 18:15, 11 August 2013 (UTC)

Steve Baker makes an obvious point about overtones. Im not sure how an Undertone can be generated on a bass. In fact it cant. Obviously the body on a bass fiddle will make a difference to the sound, but what about an EUB. A 3/4 size EUB with 41 in long scale (and thicker strings) sounds completely different from a fretless bass with a 35in scale . Why should that be?--86.177.63.179 (talk) 18:40, 11 August 2013 (UTC)

Note, though, that the quality of a musical instrument, especially any sort of guitar, is not merely what sort of tone it has. Other qualities are how easy is it to play - some need tougher fingers than others; how well does it stay in tune; can it in fact be put properly in tune? Cheap electric guitars can have twisted or bowed necks and thus no amount of twidling of the tuning screws will put them right. Double truss and steel framed guitars, including the Rickenbacker, stayed in tune under 1960's and 1970's TV studio hot lights - that is why they were highly regarded. 121.215.13.245 (talk) 00:35, 12 August 2013 (UTC)

The studies Nimur describes have been done and are even mentioned in our article Stradivarius#Comparisons_in_sound_quality. Vespine (talk) 02:50, 12 August 2013 (UTC)

Yeah I think this thread is veering off the point. Im not talking about subtle differences between different instrument makes but the pretty damn obvious difference in sound between a real bull fiddle and a fretless bass when both are played pizzicato. Is it something to do with the strings buzzing against the fingerboard more on the bull fiddle because of the thicker strings or the greater tension?86.177.63.179 (talk) 15:18, 14 August 2013 (UTC)

Ok well to get back on point, the most obvious differences are that your finger acts like a dampener at the end of the string on a fretless instrument rather then a rigid anchor on one with frets. Also very small and subtle movements of the finger against the fret board will affect the strings vibration and tamber and the precise placement of your finger, even by fractions of a milimeter will cause the tone and pitch to be slightly different, whereas with a fretted instrument you have a fixed anchor point where it doesn't really matter precisely where you placed your finger. Vespine (talk) 00:32, 15 August 2013 (UTC)

August 11

A question of perception

First of all, this is not a medical or similar question. It is simple curiosity. Often when I am typing on the keyboard I pause to read what I have written. I have noticed many times over the years that when I look at the cursor, it appears to stop blinking for rather long periods of time (I have had the same experience looking at the blinking on my clock). Clearly the blinking has not "stopped" as it appears to have. I am curious as to whether there is an explanation for this perception (any localized space-time anomalies notwithstanding, of course). 173.35.158.194 (talk) 03:45, 11 August 2013 (UTC)

1) The cursor does sometimes stop blinking for me, when my PC is busy.

2) A blind spot might hide some of the blinking. You aren't aware of it normally, but your vision has lots of missing bits in it, say where you looked at the Sun once. Your brain fills in the missing bits as best it can, but if the entire cursor is in a blind spot, it won't recreate a blinking cursor, but will rather recreate it however it last appeared. StuRat (talk) 03:54, 11 August 2013 (UTC)

Thanks StuRat. I was pretty sure that there was nothing wrong with the space-time thingy! lol173.35.158.194 (talk) 04:13, 11 August 2013 (UTC)

I seriously doubt that blind spots have anything to do with it. The effect that you are perceiving is known as chronostasis. As that article explains, it is a result of the weird stuff that the brain does during and after eye movements. Basically the brain blanks out the visual system during a saccadic eye movement, but prevents a gap from being perceived by time-warping perception shortly before and after it. Looie496 (talk) 04:22, 11 August 2013 (UTC)

This sounds similar to some of the stuff they talked about on a recent cable TV series called "Brain Games". I forget which channel it was on (maybe NG), but a frequent topic was how our eyes deceive us, or more to the point, our brains deceive us. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:54, 11 August 2013 (UTC)

Long ao I noticed a similar phenomenon: when I looked at the second hand of a ticking wristwatch, it seemed to hold its position for longer than a second before it moved again. This had nothing to do with saccadic blanking, and nothing to do with the blind spot. It lasted longer than another complete saccade would have taken. It seemed to be a selective attention phenomenon. Edison (talk) 13:58, 11 August 2013 (UTC)

Did you read the chronostasis article? "When eyes execute a saccade, perception of time stretches slightly backward.[2] The viewer's brain registers that they have been looking at the clock for slightly longer than they really have, producing the illusion that the second-hand is frozen for more than a second." In other words, the brain alters its own memory of the past to make it seem like during the saccade, it was perceiving the clock, even though it was perceiving nothing at all. This rewriting of history is IMO one of the creepiest functions of the brain. --Bowlhover (talk) 14:10, 11 August 2013 (UTC)

I don't think that phrases like "rewriting of history" and "our brains deceive us" are the right way of thinking about this sort of thing -- both of them are implicitly dualistic. I've been working for some time on a book about consciousness and the brain (working title The Virtual Self), and the view I try to develop is that the mind is essentially a virtual entity. The relationship between perception and the brain mechanisms that implement it is complex and indirect in the same way that the relationship between what you see on a computer screen and the code running inside the computer is complex and indirect. What we are seeing in phenomena like chronostasis is the traces of that indirectness. Daniel Dennett's ideas run in the same direction. Looie496 (talk) 15:31, 11 August 2013 (UTC)

Whatever you choose to call it, it's undeniable that perception conflicts with reality in this case. The brain thinks it sees a continuous stream of images during a saccade, when in fact, it sees nothing between the initial and final head positions. The brain thinks that a clock's hands freeze right after a saccade; in reality, the clock is ticking along at the same rate it always does. --Bowlhover (talk) 07:05, 12 August 2013 (UTC)

• This sounds like a plot. You ought to see the Doctor. μηδείς (talk) 16:37, 11 August 2013 (UTC)

In school I felt like it was possible to predict success at math contests ahead of time by the degree of subjective slowing of the flashing : on a digital watch shortly beforehand, so I suspect there's a way to get at it by some similarly designed experiment. No idea if anyone has though. Computer cursors, on the other hand, are often too unreliable to say much about. Wnt (talk) 06:36, 12 August 2013 (UTC)

science )How did big bang occur?)

How did big bang occur? 223.223.150.82 (talk) 12:37, 11 August 2013 (UTC)

See our article on the Big Bang, but note that "the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe going forward from that point on." — Lomn 13:16, 11 August 2013 (UTC)

See Inflation (cosmology) and False vacuum. Count Iblis (talk) 15:38, 11 August 2013 (UTC)

There is a strong possibility that we may never know the answer to this question - because all of everything was reduced to a singularity (a zero-sized dot) at the instant of the Big Bang, any information about any previous state would be destroyed. We may (possibly) be able to deduce what we think must have happened - but we'll probably never know for sure. SteveBaker (talk) 16:45, 11 August 2013 (UTC)

It was the hand of God. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:49, 12 August 2013 (UTC)

And before you ask, I'm defining "God" as creative energy in the universe. In short, it's the same as the other answers: We don't know and never will know what started it all. If we invented a backward-time-travel machine that could travel billions of years in a reasonable time, we might be able to arrive at the starting point - just before being sucked into the singularity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:53, 12 August 2013 (UTC)

I believe it is too soon to say categorically we WILL never know. I agree it is possible that we MAY never know, but I think it is too soon to discount all possiblility. The LHC recreates conditions moments after the big bang, i don't see why it would be impossible to recreate the conditions before the big bang, even if only in computer models or something. We might never be able to prove with certainty that it IS the way it happened, but a lot of our models are "best fit" interpretations of the evidence, and the big bang left LOTS of evidence :) Vespine (talk) 23:51, 12 August 2013 (UTC)

We can theorize, but we can't know for sure, we can only infer. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:05, 13 August 2013 (UTC)

That's basically Deism, Bugs. God created evolution, saw that it was good, and went on vacation to await the results. I don't think anyone except a fundamentalist is going to demand an explanation. μηδείς (talk) 01:20, 13 August 2013 (UTC)

The OP demanded (or asked for) an explanation. Don't know if he's a fundamentalist. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:05, 13 August 2013 (UTC)

A whole buncha stuff about the big bang makes more sense if you transform your time coordinate by taking it to be the logarithm of the time after the big bang. We (well, not me, but somebody) can talk intelligently about what might have happened 1 sec after the big bang, or 0.1 sec, or 10⁻³⁵ sec, but not at the big bang — that's meaningless, or if not meaningless, then at least we haven't developed the theoretical framework to make sense of it.

So the big bang theory talks about all these things that happened very short times after the big bang, but it really doesn't talk about the big bang "itself", in the sense that we've been led to understand, with everything proceeding from a literal mathematical point. You can very reasonably take the position that the big bang, in that sense, never happened at all (which is not to say that the big bang theory has anything wrong with it, just the popular presentation of it). --Trovatore (talk) 01:37, 13 August 2013 (UTC)

I like Trovatore's explanation.

My view is that the phrase "big bang" is meant to disparage (not to explain) the theory of the expanding universe, by drawing attention to the least-intuitive consequence of the model. If we assume an expansion is always occurring after t=0, then the limiting case at t=0 is sort of a conundrum. At the initial time, the whole universe is all scrunched and squished into an infinitesimal point. Theoretical people like Einstein found this notion to be preposterous.

Today, most scientists consider the expansion model to be the most plausible explanation for the universe as we see it today. Theorists are progressively getting better at describing how the early universe evolved, and as the models improve, we can explain more quantitative details about events at times closer to zero. But as we get arbitrarily close to zero, there's very little to predict: everything is all in one place, and very few of the fundamental interactions are meaningful over such miniscule timescales. All that is really relevant, when describing a densely-packed miniature universe, is some pretty abstract physics related to the way that symmetry of fundamental interactions changes at incredibly high energy densities. Nimur (talk) 12:22, 13 August 2013 (UTC)

Well, these things leave their signatures in the the cosmic background. E.g. you can observe from the cosmic backround alone that the traditional Big Bang model is wrong and that inflation theory is far more likely to be correct, despite the fact that the photons from the cosmic background that you observe come from an epoch when the inflationary epoch had long ended. Count Iblis (talk) 13:01, 13 August 2013 (UTC)

State of matter of large biological molecules

I suppose most large biological molecules like proteins and enzymes are rarely or never found in isolation. But if you could purify them into a macroscopic quantity, is it safe to say that they would invariably be solid at standard temperature and pressure? If not, how can one determine the state of matter for such compounds? It seems the Wikipedia articles for such compounds never list this information. —Psychonaut (talk) 17:09, 11 August 2013 (UTC)

They are, in fact, going to always be solid. For any molecular substance, the predominant forces on the molecules working to hold it together are going to be london dispersion forces and dipole-dipole forces. In small molecules, london forces are relatively weak, but they increase roughly with molecular mass; because molecular mass roughly correlates with polarizability. That is to say that larger molecules are more polarizable, so will be more subject to london dispersion forces. Even for a relatively non-polar molecule like a hydrocarbon, any molecule larger than about Icosane (C₂₀H₄₂) is going to be solid. Icosane has a molar mass of less than 300 g/mol. Any biological macromolecule will have masses in the tens or hundreds of thousands; at room conditions any pure substance composed of molecules that large will be a solid. --Jayron32 17:39, 11 August 2013 (UTC)

It is routine to determine the structure of proteins by purifying them to produce crystals, and then to use X-ray crystallography. — Quondum 19:40, 11 August 2013 (UTC)

Thanks, Jayron32 and Quondum, for the explanations. You say that any molecule larger than about C₂₀H₄₂ is always going to be solid. What about smaller molecules like C₆H₁₂? There are about two dozen different isomers; are they always going to be liquids, or might some of them be solids or gases? —Psychonaut (talk) 20:34, 11 August 2013 (UTC)

The hexenes are liquids at standard temp and press. Eg 1-hexene melts at 133 K, boils at 336 K; 2-hexene melts at 130 K and boils at 342 K. All the hexenes melt in the range 130 to 134 K and boil in the range 335 to 347 K. See Chemspider and NIST data. 121.215.13.245 (talk) 00:49, 12 August 2013 (UTC)

• To get an intuitive grasp, consider that Tungsten hexafluoride is one of the heaviest gasses at room temperature, and while pentane boils between 9 and 36 centigrade, hexane is a liquid at room temperature. (Make sure you look at the articles and molecular diagrams). μηδείς (talk) 01:02, 12 August 2013 (UTC)

There are a few good examples, like powdered milk which is largely casein, contact lens cleaner tablets made out of subtilisin or pancreatin (a mixture) - I think the widest range can be found in Japanese cooking which seems to have really gotten into the idea of isolating enzymes and predigesting food with them, but I don't know much about that - and (in wet form) the crystallins making up much of the cells of the lens of the eye ... anyway, by and large these proteins and proteins in the lab tend to end up looking like white powders, with some colorful exceptions like myoglobin which is ruddy from the heme (also I suppose dried blood is probably >50% hemoglobin come to think of it, but I haven't verified that). Wnt (talk) 06:08, 12 August 2013 (UTC)

Can a zebra be ridden like a horse ?

Not having seen this (except in the movie Sheena, where it was probably just a painted horse), I assume there's some reason why this doesn't work as well as riding a horse or donkey. StuRat (talk) 19:15, 11 August 2013 (UTC)

I imagine that there is indeed a reason, and that wild horses can't be ridden for the same reason. In other words, I don't think a zebra would allow a human to mount it and ride it. The domestication of the horse didn't occur overnight. Surtsicna (talk) 19:25, 11 August 2013 (UTC)

See Zebroid for attempted workarounds. Hcobb (talk) 19:32, 11 August 2013 (UTC)

Here's a video of a horse trainer using Monty Roberts' "horse whispering" method on a zebra on the fourth day. (Monty can "break" wild horses on the first day.) I don't have a good source, you can google "horse versus zebra"; but horses tend to live in packs like dogs, with an alpha member, while zebras live in large herds and are more skittish and less interactive. μηδείς (talk) 22:02, 11 August 2013 (UTC)

Zebra#Domestication says "Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. Most of these attempts failed, though, due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between any species of zebra and a horse, pony, donkey or ass) are preferred over purebred zebras."

I vaguely recall reading that the WWI German Army attempted to domesticate Zebra for military uses in Africa with very little success. They simply haven't had the thousands of years of selective breeding that produced the modern domesticated horse. SteveBaker (talk) 03:49, 12 August 2013 (UTC)

See http://www.dailymail.co.uk/news/article-1190753/Racehorse-trainer-rides-pet-ZEBRA-pub.html . The greatest thing about biology is that it just plain doesn't know theory, no matter how hard you try to teach it. Wnt (talk) 06:11, 12 August 2013 (UTC)

No. Zebras' backbones are not like horses'. The former can bend down and the latter locks when you put pressure on it. — Preceding unsigned comment added by 83.60.174.74 (talk) 11:10, 12 August 2013 (UTC)

Can you give us a source for that? If true you would think it would be more widely reported. μηδείς (talk) 16:44, 12 August 2013 (UTC)

I've heard the same thing, apparently zebras can't handle the physical strain of added weight during riding. I suppose they can handle a light-weighted person. However, they are still useful for pulling weight as the photo suggests. Sorry, I have no reference. Plasmic Physics (talk) 01:11, 13 August 2013 (UTC)

I believe that even I have heard the same thing. But I spent a good while looking for sources when this was posted and came across no such comment. I don't remember Gould mentioning it in his essay on What is a Zebra either. I suspect it's an old wives' tale. μηδείς (talk) 01:17, 13 August 2013 (UTC)

OK, thanks all. So, alas, no zebra polo games. :-( StuRat (talk) 07:49, 15 August 2013 (UTC)

Low testosterone in women and low estrogen in men

I was wondering what the term is for when a man does not have estrogen and a woman does not have testosterone. Is it seriously Low-T and Low-E? I thought Low-T was a term made up by advertisers. Also; if someone had literally no amount of the opposite sex's primary sex chemical in there body; would that person have to be dead or dying? — Preceding unsigned comment added by 174.16.180.165 (talk) 20:38, 11 August 2013 (UTC)

Hypogonadism, hypoandrogenism, hypoestrogenism.

As for losing all trace of testosterone or estrogen: It is relatively easy for people of either sex to lose their gonads, but searching "extraovarian estrogen" I pull up lots of sources like [1] and likewise for "extratesticular testosterone" [2]. Mostly the adrenal but apparently also various GI tract tissues. The other way is to lose the enzymes to make them: apparently some of these lead to genuinely no detectable testosterone [3]. Wnt (talk) 06:31, 12 August 2013 (UTC)

is this poison ivy???

hello, can someone please help me identify this plant? -->http://i.imgur.com/OhPITzn.jpg my dad thinks its poison ivy, but i think its just a weed wrapping around the rake. this is near ottawa, ontario, canada. thanks. 208.96.87.57 (talk) 20:43, 11 August 2013 (UTC)

I would expect a glossier, shinier leaf on poison ivy; so I would suspect that is some other plant with similar leaf shape. If you aren't sure, err on the side of caution. Nimur (talk) 21:16, 11 August 2013 (UTC)

It's poison ivy all right, a fine healthy specimen (pretty, isn't it?). While poison ivy leaves can be glossy, it's not diagnostic. Mature leaves tend to be shinier and more potent. Handle with care, wear disposable gloves, and wash everything including yourself, don't touch your eyes, face, etc. I've learned to identify poison ivy from repeated, itchy personal experience. Acroterion (talk) 21:23, 11 August 2013 (UTC)

my guess is Hog peanut Amphicarpaea bracteata--Digrpat (talk) 23:22, 11 August 2013 (UTC)

Hog Peanut looks correct. Hog peanut has two large side veins that branch out from the base of the leaf forming a hen's foot, while poison ivy has about a dozen indented veins at right angles from the main vein like comb tines. Of course it is not worth the risk, so just treat it as if it were poison ivy. μηδείς (talk) 00:30, 12 August 2013 (UTC)

August 12

Engine brakes restricted.

I see such signs on American freeways. Why? My guess is because it is hard on the road? But I want to get a confirmation and perhaps an extended explanation why it is so.

Also why restricted? Why not prohibited? Is restricted the same as prohibited? I don't think so?

Thanks, - Alex174.52.14.15 (talk) 03:09, 12 August 2013 (UTC)

I think it's because of the noise it makes which disturbs the residents. "Restricted" probably means "for God's sake, if you're going to crash otherwise, then go ahead and use them". StuRat (talk) 03:21, 12 August 2013 (UTC)

What are "Engine breaks"?? Or is "Engine braking" what is meant? Rojomoke (talk) 05:39, 12 August 2013 (UTC)

See engine braking for details on how to use the engine to slow down a vehicle. The signs most likely refer to compression release engine brakeing, which is common on heavy vehicles, efficient and very, very noisy... WegianWarrior (talk) 06:19, 12 August 2013 (UTC)

The signs often seen are about brake retarders. And yes, if you see signs, it must be about the noise. For some reason American government has a fixed idea that anything having to do with noise, even on vehicles that travel interstate, has to be handled at the township ordinance level ... but on the other hand, the moment someone makes an electric car that is quiet, the federal government leaps in to regulate them to be louder lest a blind person not hear it. Wnt (talk) 06:42, 12 August 2013 (UTC)

The fed gets into the act because of laws connected with various physical handicaps. Being able to hear well is not considered a handicap. The Congress has the power to regulate interstate commerce, and they might be able to pass such restrictions if there was a lobbying / advocacy group. Which there probably isn't. The hearing-impaired would have lobbyists. The nearing-unimpaired probably don't. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:37, 12 August 2013 (UTC)

I recall there was a lot of concern raised about the noise level of the Concorde, but the article doesn't say what, if anything, was actually done about it, nor whether the federals got involved or not. It reads kind of like they did, but it's not stated explicitly. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:45, 12 August 2013 (UTC)

I believe that the Concorde flight paths into New York were the subject of lengthy negotiations, and it was never allowed to fly across the continent. These negotiations took so long that, although it was clearly designed for the London - NY route, the inaugural flight was to Bahrein. Alansplodge (talk) 15:21, 12 August 2013 (UTC)

"Scheduled flights began on 21 January 1976 on the London–Bahrain and Paris–Rio (via Dakar) routes... When the US ban on JFK Concorde operations was lifted in February 1977, New York banned Concorde locally. The ban came to an end on 17 October 1977 when the Supreme Court of the United States declined to overturn a lower court’s ruling rejecting efforts by the Port Authority and a grass-roots campaign... Scheduled service from Paris and London to New York’s John F. Kennedy Airport began on 22 November 1977." (See Concorde) Alansplodge (talk) 15:26, 12 August 2013 (UTC)

I've been under the impression that the engine braking involves the electrical generator. When the diesel fuel is cut off the truck moves forward under the gained momentum. The rotation of the wheels is eventually transferred to the generator which generates electricity that is stored in the rechargeable battery. The work invested in the process slows the truck down. The article quoted above does not mention this at all. — Preceding unsigned comment added by 174.52.14.15 (talk) 04:50, 13 August 2013 (UTC)

That's regenerative braking, aka KERS. With "normal" cars, it is a parasitic effect that cannot be controlled and is too weak to brake the vehicle significantly. Engine braking makes the engine use kinetic energy to compress air, thus the noise when the air escapes. - ¡Ouch! (^{hurt me} / _{more pain}) 08:18, 13 August 2013 (UTC)

In detail: Engine braking means putting the vehicle into a lower gear and taking your foot off of the gas. When that happens, the cylinders in the engine don't get much fuel - so the down-strokes aren't producing much energy - but the up-strokes still have to compress the fuel-air mixture, and that consumes energy. When the engine is running slowly, the energy from the burning fuel produces more energy than is needed to compress the gasses. But when the engine is forced to run at high RPM (because we're in a very low gear for the speed) and there is too little gasoline present - the energy to compress the gasses by far exceeds the gain from burning that fuel. This energy comes from the kinetic energy of the vehicle - which must therefore slow down. This process is noisy because there is suddenly a hell of a lot more air being pushed out of the exhaust than normal. SteveBaker (talk) 16:31, 13 August 2013 (UTC)

IUPAC additive nomenclature

How do I choose the central atoms in ambiguous cases?

For the sake of argument, an example: H
₂F⁺
- how would I decide between μ-fluorido-dihydrogen(1+), dihydridofluorine(1+), or dihydrogenfluorine(2 H—F)(1+)? Plasmic Physics (talk) 03:29, 12 August 2013 (UTC)

Is this a technically correct name for [Be]=B[Be]B1[Be]B([Be]B=[Be])[Be]1: di-μ-beryllido-1κB-bis(μ-beryllido-beryllido-2κB-diboron)? Plasmic Physics (talk) 12:55, 12 August 2013 (UTC)

Creep Rate Tensor

I am modeling a pressurized cylinder at high temperature, for which i have a creep rate equation (which involves hoop stress) to calculate hoop strain and it states that stresses in other directions are not important. Now i have to prepare a creep rate tensor (3x3 matrix). Can somebody tell me which components will be entered in the matrix and which will be zero?Brahmarishiraj (talk) 04:23, 12 August 2013 (UTC)

Found this by Googling. Mentions creep rate equations and tensors. You may understand. http://sundoc.bibliothek.uni-halle.de/habil-online/06/06H055/t3.pdf --86.177.63.179 (talk) 16:02, 14 August 2013 (UTC)

Lymph node removal and blood pressure measurement

In cases of breast cancer, depending on the surgeon's judgement, some or all of the armpit lymph nodes will be removed. This will reduce the effectiveness of fluid drainage of the arm on the affected side. Women are advised to not allow blood pressure to be checked on the affected arm. But if the woman some time later develops breast cancer in the other breast, she may lose the lymph nodes for the other arm as well. How does this affect the measurement of blood pressure, given that it is done by gradually inflating a cuff on an arm while listening for the aparent start and stop of the pulse? Is the high reading increased due to back pressure or something? Or do you get a false low reading from cutting off the perceived pulse early? 1.122.88.140 (talk) 05:45, 12 August 2013 (UTC)

How do I compute the charging time for Li-ion battery?

I read that the simple formula is Battery_capacity x Battery_type_coefficient / Charger_current_supply. But I couldn't find what coefficient I should use for Li-ion. Zarnivop (talk) 09:16, 12 August 2013 (UTC)

For safe charging that preserves battery life, a Lithium-ion battery requires a non-linear charging cycle. Many have some control circuitry built into the battery, but you need to study charging graphs before attempting to charge this type of battery on a home-made charger. Dbfirs 11:03, 12 August 2013 (UTC)

But the charger is not home made... Zarnivop (talk) 14:38, 12 August 2013 (UTC)

If it's designed for that particular battery, then it will stop charging (and most likely indicate this) when it has finished the charging cycle. The time will vary depending on how deeply discharged the battery was, and what charging rate it deems appropriate. The charging sequence usually measures the rising voltage of the battery to determine when to stop charging. Dbfirs 20:38, 12 August 2013 (UTC)

It does. I wanted to know beforehand, and deduced erroneously that the formula for Ni-Cd batteries will work for Li-ion. The fact that the charger states "Output: 4.2V, 350mA±50mA" supported my error. My bad. Zarnivop (talk) 11:04, 13 August 2013 (UTC)

plasma of blood and plasma of television

what is the connection between the plasma of blood to plasma of television? 176.13.43.43 (talk) 18:43, 12 August 2013 (UTC)

None whatsoever, except that the two words are based on the same Greek word. See [[4]]. Dominus Vobisdu (talk) 18:55, 12 August 2013 (UTC)

The root is also found in words such as protoplasm and ectoplasm. AndrewWTaylor (talk) 18:58, 12 August 2013 (UTC)

Not so fast. In some people's worlds, televisions drip blood. -- Jack of Oz ^{[pleasantries]} 20:53, 12 August 2013 (UTC)

I don't know much about blood plasma, but the other plasma is any matter where the bulk phase has a certain set of properties. The underlying property, which gives rise to others, is the existence of charge separation or presence of a net charge. The most basic type of plasma would be a substance where some of the electrons are not bound to atoms, but move freely within the bulk phase. To become a plasma, a substance needs to undergo ionisation. Plasma is often called a state of matter, but unlike melting, and boiling, ionization does not happen at a precise temperature, it is a gradual process. As temperature increases, a larger fraction of the bulk ionised. This process is also reverable, though a process called recombination, where electrons are literally recombined with ionized atoms. Usually, ionisation and recombination occurs in an equilibrium. There exists a large variety of plasmas: solid plasmas, liquid plasmas, gaseous plasmas and more; of which gaseous plasmas feature the most often. Metal is considered an obscure example of plasma, since its electrons are free to move throughout the bulk, although the atoms are more or less bound within the crystal lattice, but don't be fooled, the atoms also slowly diffuse throughout the lattice. Plasmic Physics (talk) 01:33, 13 August 2013 (UTC)

A weird 100 F happen around Cape Horn

How can this every happen. I thought 100 F is a b-s joke at the tip of South America. But when I look at 42 F is the dew point, 14% humidity, a high temperature is possible. Is this possible a sudden spike jump in temperature in just one hour. The weather report said 7:00 PM is 53 F but 100 F is 8:00 PM but 9:00 PM is 51. Do 30-40 degree jump in temperature ever happens? Is this possible to start as 75 F at the midnight. At Southern hemisphere January is their summertime, at the high latitude can peak temperature happen at midnight hours, could it be due to constant daylight, and only 4 or 5 hours to release heat make peak temperatures occur at night hours. At low latitudes we never have peak temperature at night or midnight or sudden 20-30 F jump in just one hour.--69.226.33.213 (talk) 20:27, 12 August 2013 (UTC)

While a temperature like that could in principle happen, a cursory reading of the data strongly suggests that the report of 100F is in error. First, as you've noted, the temperature on either side of that one reading on the day in question is far lower. Second, the all-time high temperature for any of the days nearby is around 62F. Between those two pieces of data, it's reasonable to assume that the 100F reading is not reliable. — Lomn 20:44, 12 August 2013 (UTC)

Could the inaccurate bizarre reading be due to the thermometer is malfunctioning? Maybe the instrument may not be working properly at that time. Is this possible sometimes there is something technological wrong with thermometer somebody just caught it and fix it.--69.226.33.213 (talk) 03:33, 13 August 2013 (UTC)

One of the downsides to a "Web 2.0" data aggregator like Weather Underground Weather Underground is that the data is rarely checked by human; and its source is totally opaque. A comment on the website implies that the website is aggregating METAR data. Now, I only trust one source for my METARs: the National Weather Service (or any of their other authorized reporting services) - and since station data is already available for free online, and the website will even translate it into plain English for you... I can't possibly understand why anyone should ever choose to visit dubious second-hand sources like Weather.com and Weather Underground - websites chocked full of pretty (useless) graphics and animations and loads of extra cruft and advertisement. http://weather.gov - provided by the United States National Weather Service - has excellent worldwide data - even for Southern Argentina. (Where do you think wunderground.com gets their free data!?) NOAA also archives weather and climate data on their website.

As a last note: a METAR ending in $ indicates malfunctioning equipment. If you don't see a $ then there was no diagnosed equipment failure. This is documented in the METAR format specification in Advisory Circular AC-0045G Aviation Weather services, available for free online at NWS, NOAA, and FAA's websites, none of which work well with a hot-link to the PDF. Personally, I keep a paper copy of Aviation Weather Services in the small bookshelf next to my bed at all times, for quick reference. Nimur (talk) 05:05, 13 August 2013 (UTC)

August 13

Who burns more calories

I was reading calories burnt per hour lists of various sports and it got me thinking, would a fat out of shape person spend more calories than a fit person in the same activity even if he did less of it? For example if a fat guy runs for 10 minutes and is absolutely exhausted and faints would he spend more energy than a fit person who runs 20 minutes and does not even feel tired? — Preceding unsigned comment added by 88.195.215.49 (talk) 07:34, 13 August 2013 (UTC)

(Note: Wikipedia does not offer medical advice - this is not authoritative) There is a distinction to make between the amount of fat burned and energy spent. The answer is that it depends, based on how efficient that fat person is, the weights of both, the exercises involved, the conditions, and the exact lengths of time.--Jasper Deng (talk) 07:45, 13 August 2013 (UTC)

Your question can't be answered as asked, but a few things to help you on your way:

How exhausted a person feels is not a measure of how much energy they've used. If two persons ride exercise bikes and spend the same amount of calories in the same time the person in better shape will feel less exhausted even if they spent the same number of calories.

Generally speaking, a heavy person will burn more calories per mile running, but it depends very much on how efficient that person's running style is, and to some extent on the speed. Sjö (talk) 08:22, 13 August 2013 (UTC)

I'm aware of formal measurements that are made on people with physical disabilities, such as cerebral palsy, that demonstrate that such people use considerably more energy than able bodied people to perform the same task. It's reasonable to guess that obese people would too. HiLo48 (talk) 08:14, 13 August 2013 (UTC)

See here for some figures. Count Iblis (talk) 12:49, 13 August 2013 (UTC)

• Muscles have a much higher resting metabolism than fatty tissue, burn more calories, and require a specific diet to maintain at a weightlifting level. See Basal metabolic rate. μηδείς (talk) 23:30, 13 August 2013 (UTC)

I remember an experiment we did at school which is different but related. Everyone had to run up a few flights of stairs and was timed doing it. We calculated how much energy you burned (weight times height) and divided it by the time, the theory being that the more energy you can produce in the shorter amount of time is basically how "fit" you are. Turns out, the most overweight people, even thought they were slower, were actually the most "fit" and the most skinny people were the least fit. Of course this is purely by people's energy output, it says absolutely nothing about health. Vespine (talk) 02:20, 14 August 2013 (UTC)

Seat collision for swing ride caused by wind - how?

WindSeeker is closed during high winds, evidently because its seats, probably even despite the dampers present, collide when the air is in motion. The article, not unexpectedly, doesn't discuss the physics.

So, I did a thought experiment for a very simple case, where the velocity field of the wind is constant, and the air density is assumed constant. I know these are approximations that are probably not valid in real life, but I first figured I should start with this special case, where the simple drag equation is at least approximately applicable. I then made the assumption that the hinges attaching each seat's support bar to the rotating gondola allowed complete freedom of motion (again, the dampers are there to hinder it, but again, I have to simplify the problem a bit), thus not considering the friction of the hinge. With this, I began doing the vector addition of the wind's and seat's velocity fields so I could then calculate the drag force with the resultant relative air velocity. However, doing it mentally, it still didn't quite dawn on me why this should cause the seats to collide, nor the maximum safe wind velocity predicted by my simple model. I don't have a very advanced understanding of fluid dynamics, so I wish the relatively simple drag equation will suffice to model this situation.

While I'm willing to accept a vector calculus explanation (and half-expect one), I'm sure the physics can't be that hard (although with a non-constant force field, I've already fixed my mind on the need to perform integration here).--Jasper Deng (talk) 08:09, 13 August 2013 (UTC)

I think it's simply that your assumption of a constant wind isn't valid. Air, like water, contains currents, where winds are higher or lower, and in different directions, and modeling this is necessary to understand the problem. StuRat (talk) 09:31, 13 August 2013 (UTC)

Even starting with a 'constant velocity wind', you can end up with oscillations - see vortex shedding. AndyTheGrump (talk) 22:11, 13 August 2013 (UTC)

Theory of Relativity

We know that maximum speed of a body can be as high as the speed of light. Now my question is that - Imagine a train is running with the speed a light and a boy runs in the train. An observer outside the train sees that boy. Then what is the speed of the boy with respect to the observer outside? If you are thinking to add the speed of the train and the boy, then it would be more than the speed of the light that is impossible.Publisher54321 (talk) 09:49, 13 August 2013 (UTC)

For the boy to run in the train, he would have to accelerate himself. But since he already has infinite mass, he can't. The situation cannot arise. 1.122.88.140 (talk) 09:59, 13 August 2013 (UTC)

And just to be clear, the reason that he cannot accelerate while he has an infinite mass, is because to accelerate any infinite mass, you need an ifinite amount of energy, which is not available in this universe. --Lgriot (talk) 11:09, 13 August 2013 (UTC)

Those answers are a bit misleading. In the reference frame of the train, the boy can accelerate in a perfectly normal way. But in the reference frame of an observer who sees the train moving at nearly the speed of light, time dilation causes the boy's acceleration to appear very small. Looie496 (talk) 14:52, 13 August 2013 (UTC)

No I beleive that your answer is misleading, Looie, becuase you didn't properly read the (poorly worded, fair enough) question. The OP did not ask about a train going near the spead of light, but at the speed of light. --Lgriot (talk) 08:21, 14 August 2013 (UTC)

The relativistic answer (for speeds below c) is given by Velocity-addition_formula#Special_theory_of_relativity. AndrewWTaylor (talk) 11:54, 13 August 2013 (UTC)

It also work for speeds at c. Dauto (talk) 14:40, 13 August 2013 (UTC)

Has anyone noticed that this is a slight modification of the very thought experiment used by Einstein when he created the theory of relativity? Plasmic Physics (talk) 11:59, 13 August 2013 (UTC)

I wouldn't draw any inferences. — Quondum 12:09, 13 August 2013 (UTC)

Strangely, I don't recall the flashlight-on-the-train explanation actually being concocted by Einstein, even though "everybody" knows that Einstein used a flashlight on a train as his example for special relativity. That example doesn't appear in the famous 1905 papers, (available in English translation on Wikimedia and at Mr. Walker's excellent website).

So, how did this bit of historical corruption occur? Who concocted a flashlight-on-a-train gedankenexperiment, and why does everybody attribute it to Einstein!? It would seem that science, like religion, is easily corrupted over the course of history, by people's relentless insistence to deify individual contributors and give them credit for creation of everything.

Einstein wrote many things, and originated many ideas. Einstein wrote about electromagnetic wave dynamics, and corpuscles of light, and some very convoluted mathematics about geometric identities between geodesics and inverse-square-law forces; (and plenty more about incorrect theoretical arcana about spectral lines that nobody ever mentions any more because it was totally wrong).

But so did thousands of other physicists. Those more-anonymous physicists had lesser egos, worse publicists, and more comprehensible writing. I put forward the bold statement: nearly everything that we know today about the photoelectric effect, the mechanisms of special and general relativity, electrodynamics, didn't come from Einstein.

So, a challenge to the reference desk: which scientist or author first published a parable of a flashlight on a train (or a person running on a train) moving with relativistic velocity? Nimur (talk) 12:45, 13 August 2013 (UTC)

Oh, Nimur. You can be such a grouch. Dauto (talk) 14:40, 13 August 2013 (UTC)

Sorry, I'll try to be more cheerful! Happy Tuesday, here's a bit of fun science-fiction to brighten your morning... actually it's probably the reason I'm so grouchy today. Let's all just conveniently forget to account for the energy consumption of the thousands of jet-engines you need to evacuate a 700-mile metal tube, and pretend that you can put an airtight metal tube in California's central valley and model its air-temperature at 68° F! Also multiply the air-compressor's required horsepower by ten in every sixth paragraph and neglect to update your overall energy budget! And vomit-inducing 3-mile-radius turns at 760 miles per hour! At least the cartoons are pretty. Nimur (talk) 15:39, 13 August 2013 (UTC)

Thanks! I was looking for the tech details earlier but missed them. Curious to observe the walls are 0.8-0.9 inch thick. [5] Wnt (talk) 22:54, 13 August 2013 (UTC)

So you admit it, not even you know who said it first? Well, I hate to pop your bubble, but I never said Einstein was the first either. So, I may yet be vindicated. Plasmic Physics (talk) 19:13, 13 August 2013 (UTC)

I admitted nothing except being slightly grouchy! Nimur (talk) 20:41, 13 August 2013 (UTC)

So, I will not be vindicated, nevertheless, my preceding statement still remains true. Plasmic Physics (talk) 21:39, 13 August 2013 (UTC)

I don't know if the question has been answered yet. I would add that just because something is not theoretically impossible, does not mean it is possible in practice. I suspect that even though relativity says mass can't travel FASTER then the speed of light, I bet that in practice mass (more then a handful of particles anyway) can't travel AT or even very near to the speed of light either. Vespine (talk) 02:05, 14 August 2013 (UTC)

"Near the speed of light" is easy: just use a reference system in which the thing has a sufficiently high speed.--Wrongfilter (talk) 12:13, 14 August 2013 (UTC)

Asthma

If a non-asthmatic person uses a Metered-dose inhaler, will it aid them in completing a marathon? Pass a Method talk 12:49, 13 August 2013 (UTC)

If it would give an appreciable advantage it would be banned from use in the sport. So, if it hasn't been banned then it has no effect. I guess it'd be treating a condition the runner doesn't have so would not improve the running. (But it could make it much worse and be unsafe.) The inhaler is for reducing constriction of the airways; do marathon runners have constricted airways as a limit on their running? RJFJR (talk) 16:14, 13 August 2013 (UTC)

Obviously that depends on what's in it. There are quite a variety of drugs that can be absorbed into the lining of the lungs - and any one of them might be dispensed this way. The more common anti-asthma drugs are corticosteroids - and steroids are pretty much banned in events like marathons - so I'm guessing they would be illegal. Whether they'd help or not is different matter. I doubt it...but I could easily be wrong. SteveBaker (talk) 16:23, 13 August 2013 (UTC)

Inhaled steroids are corticosteroids, not anabolic steroids, and I'm not sure the former would be performance-enhancing. Inhaled beta agonists might or might not help depending on the athlete and conditions. -- Scray (talk) 21:35, 13 August 2013 (UTC)

T%he standard emergency inhaler is Salbutamol - our article covers its ban in sports and the contradictory studies of its effect on healthy subjects. Rmhermen (talk) 13:07, 14 August 2013 (UTC)

Origins Of The Universe: Steady State & Big Bang Theories

What are some of the current problems and limitations of the steady state and big bang theory? 220.233.20.37 (talk) 12:57, 13 August 2013 (UTC)

For the Big Bang theory, you shoud read the article Inflation (cosmology). The steady state theory has long been debunked, you can read our Wiki articles on that subject. Perhaps also articles on Fred Hoyle (had it not been for Hoyle, steady state would have died decades earlier). Count Iblis (talk) 13:07, 13 August 2013 (UTC)

Right now, steady-state is busted, dead, gone, impossible - it's up there with "Adam and Eve" and "the Great Arklesiezure". Not even worth discussing. The Big Bang is really the only theory that explains everything - and the discovery of the cosmic microwave background radiation more or less sealed the deal. The problems are really details that are unrelated to the core fact - What caused it? What was before it? How will the universe end? What the heck is it with all of this "Dark" stuff? Those would be problems with whatever theory you might come up with though, it's not entirely clear whether the fact of the big bang has any impact on those questions. SteveBaker (talk) 16:20, 13 August 2013 (UTC)

Adam and Eve still works as a sociological metaphor, so the Steady-State theory is even less credible than Adam and Eve. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:31, 13 August 2013 (UTC)

There are still some die-hards out there such as Jayant Narlikar who maintain that the steady-state theory is viable. In his book The Primeval Universe he postulates that the microwave background radiation is due to blackbody radiation associated with helium production in stars (of necessity, the steady-state theory requires something to be making all the helium that is otherwise accounted for by the big bang). Mr. Baker, please don't shout at me, I didn't say I supported this theory. SpinningSpark 00:46, 14 August 2013 (UTC)

In relativity, whether actual mass changes or not

According to Einstein's theory of relativity, mass of a body increases when its speed or motion increases. Therefore, there is a considerable increase in mass of a body moving with a speed of 100000 km/sec. On the other hand, we know, motion of any body in Universe is relative. The body moving with the speed of 100000 km/sec must be at rest with respect to some other object in Universe, hence according to this situation there should be no change in mass. I am confused because in the first case its mass seems to change, but in the second case its mass seems to be constant. Again, this body is in motion as well as in rest with respect to two different reference frames. What should I conclude from this? Whether the mass of the object changes or remains constant? I think the correct explanation for this would be the change in mass due to speed or motion of an object depends on the relative motion of that object with respect to the reference frame from which the motion of that object is being observed. Hence, the mass of that object would be different for different frames having different relative speed with respect to that object. Correct me if I am wrong. Thanks for bearing me! Publisher54321 (talk) 18:08, 13 August 2013 (UTC)

Someone will be along shortly to explain the details, but I'm pretty sure the answer to your question can be gained from a careful reading of relativistic mass and rest mass. SemanticMantis (talk) 18:12, 13 August 2013 (UTC)

Changing to a different reference frame changes the object's velocity thus its kinetic energy (and mass per mass-energy equivalence) does indeed differ, but remember that the coordinate change applied to the object also must be applied to all other objects, thus it doesn't matter whether the ball has the energy that hit the ground or the ground it... (I wonder if it will be friends with me...) the dynamics are the same. You said the object gained mass accelerating, but incorrectly stated this: "The body moving with the speed of 100000 km/sec must be at rest with respect to some other object in Universe, hence according to this situation there should be no change in mass." However, it would have been decelerating in the new reference frame thus losing speed and mass-energy in the process until it was at rest. -Modocc (talk) 18:53, 13 August 2013 (UTC)

(edit conflict)(In the absence of an expert ... ) The rest mass (as measured in an inertial frame at rest relative to the body) remains the same in all reference frames. The preferred view is to ignore the apparent "increase in mass" because looking at the situation this way does not always give the right answer, and instead to consider the 4-D momentum vector ( but it's too long since I studied this for me to attempt an explanation!) Einstein wrote: "It is not good to introduce the concept of the mass $M=m/{\sqrt {1-v^{2}/c^{2}}}$ of a moving body for which no clear definition can be given. It is better to introduce no other mass concept than the ’rest mass’ m." Dbfirs 20:39, 13 August 2013 (UTC)

Relativistic mass is used to calculate total mass-energy (or total energy) and, for that purpose, it seems to give correct answers. Modocc (talk) 21:23, 13 August 2013 (UTC)

If you heat a body up the atoms will move faster and so the body will be heavier. Yes there is more mass. Dmcq (talk) 21:18, 13 August 2013 (UTC)

That increase of mass is due to energy in internal degrees of freedom of a composite body. Its mass (rest mass if you insist) will not change if you move the body as a whole. Similarly, the mass excess of a nucleus (possibly the clearest manifestation of E=mc²) is due to the fact that the nucleus has internal degrees of freedom. --Wrongfilter (talk) 21:30, 13 August 2013 (UTC)

Hawking radiation and the formation of black holes.

For the first part of my question, assume an observer falling in to an existing black hole which is emitting Hawking radiation. As the observer approaches the horizon, my understanding is that the observed temperature of radiation would increase, tending towards infinity at the horizon (or at least the Planck temperature shortly before the horizon). As a result, the infalling observer would observe a greater emitted power from the hole as they fell toward the horizon, and as a consequence a greater mass loss rate than an observer at infinity. So would the infalling observer see the black hole radiate itself away before they actually crossed the horizon? If so, would they see it radiate itself away before the radiation reached trans-Planckian temperatures (or, at least, would the observation of trans-Planckian temperatures be delayed until the observed remaining mass was on the order of the Planck mass)?

For the second part of my question, section 3.8 (on page 26) of this article states that a collapsing object that does not collapse to within its Schwarzschild radius will emit Hawking radiation until the collapse stops (actually it doesn't quite state that directly, it states that the object will stop emitting Hawking radiation when the collapse stops, the article is agnostic as to whether Hawking radiation is emitted from any object in the first place, but the implication seems to be that if Hawking radiation is ever emitted, it will be emitted by collapsing objects as long as the collapse continues).

So the question then is whether, as the radius of a collapsing object approaches its Schwarzschild radius, Hawking radiation in the vicinity of the event-horizon-to-be will be intense enough that the object will lose mass quickly enough that its radius is never smaller than its Schwarzschild radius? In other words, if Hawking radiation in fact occurs, does it prevent the interior portion of the Schwarzschild geometry from ever actually forming, so that objects that are asymptotically close to being black holes in terms of exterior spacetime geometry might exist, but no black holes per-se actually do exist? — Preceding unsigned comment added by Linguofreak (talk • contribs) 21:58, 13 August 2013 (UTC)

I don't understand it, but it is tied in with the Unruh effect somehow. The event horizon is a line that is continually accelerating against the rest frame. The Unruh radiation is seen because it is accelerating. If you're falling in, you're not accelerating, so what looks like an infinite energy vacuum to the event horizon looks like a just plain vacuum to you. I think. Note that there is also some absurd time dilation going on in the event horizon time frame - all that extra Hawking radiation isn't piling up in the region between event horizon and infinity, so the amount going on at any given moment (faraway rest frame time) at the event horizon must actually be very small. Wnt (talk) 23:08, 13 August 2013 (UTC)

AM radio reception (unconventional)

The AM radio station WLW once broadcast at 500kW, and could be heard across much of the globe. Our article says there are reports from people living near the tower, who claimed to hear broadcasts through the coils of their mattress springs:WLW#History. The cited ref acknowledges that these reports are to be treated skeptically. But I wonder: is it conceptually possible for a very high power AM broadcast at 700kHz to stimulate audible vibration in a spring? More far-fetched: is it possible for for a spring to act as antenna and speaker, so that the actual signal being sent is demodulated and heard faithfully? I've seen lots of "yes" (and "no") answers via googling, but few that were explained scientifically or inspired much confidence in their reliability/authority. Thanks, SemanticMantis (talk) 22:05, 13 August 2013 (UTC)

Seems to me there have been stories of people picking up radio frequencies in the fillings of their teeth, so anything's possible, especially if you're close to the source. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:28, 13 August 2013 (UTC)

The scientific explanation you are looking for is magnetostriction. Close to a powerful transmitter almost any piece of ungrounded metal will mechanically vibrate in sympathy with the RF transmission. I recall a case during refurbishment of the BBC's medium wave Brookmans Park transmitting station (in the 1980s iirc) that Radio 2 came blaring out of the newly replaced heating radiators because the pipework had not been properly RF earthed. All test equipment brought onto the site had to be specially custom modified for RF decoupling otherwise it would pick up the transmission rather than measure what it was supposed to be measuring. It could even be destroyed. The perimeter fence around powerful transmitting stations have to be earthed with ground spikes at regular intervals to prevent dangerous voltages being induced. SpinningSpark 00:07, 14 August 2013 (UTC)

...and I see that they are still causing problems for the local residents 30 years later. SpinningSpark 00:20, 14 August 2013 (UTC)

Lucille Ball always claimed that she could hear radio stations through the fillings in her teeth (There is a brief mention of the story in Lucille_Ball#Later_career - and a more complete rundown over on Snopes). I suspect she added much to the claim that this happens - but her story doesn't exactly hold water. She claimed to have heard a Japanese spy network transmitting somewhere in California and that her report led to them being captured. Sadly, there doesn't seem to any actual information that it really happened - so it's very likely to be a complete fabrication. But I think that her public retelling of this story in numerous books and interviews is where the whole thing started. SteveBaker (talk) 02:10, 14 August 2013 (UTC)

I challenge the claim that WLW could ever have been "heard across much of the globe." Maybe it could have been heard across much of the continental US, not including Alaska and Hawaii, but including parts of Mexico and Canada, if local stations with the same frequency engaged in a "Silent Night" wherein they shut down for an hour or so to allow local listeners to DX, as was sometimes done in the 1920's. The WLW AM frequency is probably too low for the short wave skip propagation which allows reception half the world away. And 50 kilowatts is more likely as a US "clear channel" station than the claimed 500 kW, though I stand ready to be corrected by reliable sources. Some Mexican stations might have transmitted at 500 kW. Edison (talk) 06:03, 14 August 2013 (UTC)

You may be to a certain extent wrong. The wikipedia article states that the 500 KW transmitter was used to broadcast to US troops in Europe at the close of World War 2. With tube radios featuring low intermodulation distortion, and the generally less noisy conditions before the proliferation of home elctric goods in the 1950's, 50 kW AM stations could be heard up to 2000 km away. Using 10 times the power with top loaded antennas that suppress high angle radiation, you get a bit better than root-10 times the range, ie about 7000 km in this case. While sky wave propagation requires frequencies above the AM band, the lower frequency you go, the better the ground wave follows the curvature of the Earth. Once the ground wave gets to an ocean, it follows the curvature of Earth with somewhat less attenuation. So coverage of at least half the surface of the Earth is possible, perhaps more. 1.122.88.140 (talk) 06:54, 14 August 2013 (UTC)

• Thanks all, especially SpinningSpark. So, it seems that getting audible vibration is fairly reasonable with the right setup. I understand why e.g. fences would need grounding to shunt off induced currents, and the basic idea behind magnetostriction. But I'm still confused on how a single spring or radiator (no resistors, transistors, etc) could act to demodulate an AM signal, so that the actual broadcast is heard, and not just some rhythmic "vibration in sympathy". Wouldn't it have to do something similar to that described at Demodulate#AM_radio? I suspect that this would rely on some really good luck regarding the nature of the spring, and the frequency of broadcast. That is, I don't expect to have any old spring act as a complete radio whenever it's sufficiently close to a powerful broadcast. Does that sound right? Bonus question: could I "tune" a spring to work this way for a specific broadcast tower/frequency, provided that I can get rather close to a 50kW AM tower? SemanticMantis (talk) 15:37, 14 August 2013 (UTC)

August 14

Ship traffic controller

Is there some kind of ship or sea traffic controller for straights and such? Or how do they know that ships won't crash? OsmanRF34 (talk) 00:56, 14 August 2013 (UTC)

If by controllers you mean the equivalent of air traffic controllers then no, they do not exist in international waters. However, in some busy lanes there are Traffic Separation Schemes where conventions are set by the International Maritime Organization that all ships are expected to follow. An example is the Dover Traffic Separation System which covers the busiest shipping route in the world, the English Channel. SpinningSpark 01:20, 14 August 2013 (UTC)

Air traffic controllers operate mostly only around airports right? Not general "international air space". Similarly, I thought shipping ports had controllers. There is a big tower at the port near where I work that even looks like an air traffic control tower. The only reference I could find after a very quick search is this [about the control at Sydney harbor. Vespine (talk) 01:28, 14 August 2013 (UTC)

Ports tend not to be in international waters. That is a very different situation. Shipping will be controlled by the port authority and ships will often be required to take a local pilot on board while entering and exiting. Your statement about air traffic controller is also incorrect. Regions outside airports can also be controlled airspace - airways for instance. In England there is almost nowhere that is not controlled airspace by someone. See also North Atlantic Tracks as an example of controlled airspace in international airspace over the Atlantic. SpinningSpark 01:52, 14 August 2013 (UTC)

The most accurate way to say it then would then be, in some places yes, but in most places no. Mingmingla (talk) 03:59, 14 August 2013 (UTC)

Not all air traffic controllers work at an airport, see Area Control Center. Some of those controllers may be responsible for international air space. CambridgeBayWeather (talk) 05:54, 14 August 2013 (UTC)

Straits as well as ports may require pilots. See [6] to hire a pilot for the Detroit River (err, strait) Rmhermen (talk) 12:51, 14 August 2013 (UTC)

How is this slide possible?

Can anyone enlight me how come the car in this [7] doesn't flip over? It's sliding some fair distance, velocity perpendicular to the wheels direction. How is that possible? Zarnivop (talk) 13:11, 14 August 2013 (UTC)

C'mon, it's 9GAG, it's probably manipulated or something. ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 13:14, 14 August 2013 (UTC)

Loose dirt. Low center of gravity. Professional driver. --Onorem (talk) 13:19, 14 August 2013 (UTC)

Drifting (motorsport) - In the interest of actually also providing a ref. --Onorem (talk) 13:24, 14 August 2013 (UTC)

The video looks speeded up to me. Otherwise, it looks like fairly typical rally driving on a low-grip surface. AndyTheGrump (talk) 13:20, 14 August 2013 (UTC)

See also Scandinavian flick. AndyTheGrump (talk) 13:28, 14 August 2013 (UTC)