Wikipedia:Reference desk/Archives/Science/2012 September 4

= September 4 =

Reference frame for Dark Energy
Does Dark Energy have a preferred reference frame or is the value constant at every velocity? If it is frame invariant, then how do two different observers at different velocities come up with the same predictions for how galaxy clusters will evolve over time? If it does have a reference frame, then what is this and how do we determine what it is and how fast we are moving relative to it? Hcobb (talk) 01:09, 4 September 2012 (UTC)


 * It's frame invariant. I don't really understand your second question. Galaxy clusters aren't frame invariant—they have a state of motion. -- BenRG (talk) 01:54, 4 September 2012 (UTC)


 * Let's do a little thought experiment. Take two massive objects and place them at rest with respect to each other and exactly the right distance from each other so that the gravitational acceleration towards each other is exactly the same as the expansion of the Universe between them due to Dark Energy. These two masses will with respect to a stationary observer remain at rest with respect to each other. Now take another observer who is moving into these objects with them lined up in front of him. Do to his high speed he will see that these objects have increased masses and a reduced distance between them. Therefore from his point of view the normal level of Dark Energy is no longer sufficient to balance out the gravitational attraction, and so these two objects MUST be accelerating towards each other. So you have two different observers applying the same laws of physics and getting radically different results. Hcobb (talk) 02:24, 4 September 2012 (UTC)


 * You can't just plug the "relativistic mass" into Newton's law of gravitation to find the force and the acceleration. Instead, you would have to include the full momentum and energy, and use the relativistic form of Newton's second law too.  Do this, and you'll get the same result in all frames of reference.  --Amble (talk) 15:27, 4 September 2012 (UTC)
 * Actually, the thought experiment is more problematic than that. A Newtonian picture of gravity gives the wrong answers when high speeds are involved, even with a fully sophisticated application of special relativity to Newtonian gravity.  Indeed, one of the earliest confirmations of general relativity was Eddington's observation of star light deflected by the sun being incompatible with a combination of Newtonian gravity and special relativity.  Pure Newtonian gravity says that light isn't deflected by gravity, because it has no mass.  Special relativity as applied to Newtonian gravity says that light should be deflected (a photon's mass being given as per E=mc2), but it gives the wrong value for the amount of deflection by a factor of two.  The moral of the story is that when high speeds are involved, you have to view gravity from a general relativistic viewpoint, not as a force that causes an acceleration.  Red Act (talk) 06:42, 5 September 2012 (UTC)

Dental question: Toothbrush vs. Toothpaste
I have a question about brushing teeth. Viewed from a high level (obviously), what percentage of the benefit comes from the brushing, and what percentage comes from the toothpaste? Phrased differently, perhaps, could it be said that brushing one's teeth without toothpaste gives about 80% of the benefit of brushing with toothpaste? 50%? 20%?  Thank you in advance! Stingray Xray (talk) 01:25, 4 September 2012 (UTC)


 * This is an awkward question as brushing and the paste each serve different functions. Assigning a percentage benefit to brushing and to the paste implies that if you omit one, you'll still get the remaining percentage benefit - it doesn't work that way.  Its a bit like asking what fraction of the motional benefit of a car comes the engine & transmission, and from the car body.
 * The main function of brushing is to disloge food particles, and rub the paste on the teeth. Toothpaste has several incredients, each designed to serve different roles.  The main ingredient is an abrasive, typically pumice powder.  The abrasive serves to remove food & bacteria stains and keep down tartar  (deposits of minerals and baterial films).  Modern toothpastes usually include a chemical that tends to weaken tartar, and antibateria agents, both of which may provide a small additional benefit above what the abrasive does.  The next significant tootpaste incredients are directed at giving a nice taste in the mouth.  Toothpaste packaging and promotion often includes mention of other things like delivering flouride, (However the chemistry of flourine means that any such benefit is negligible or completely non-existent), and reducing bad breath (however, if you are healthy, eat normal food, and are reasonably good at cleaning your teeth, you won't have bad breath anyway.)
 * So, if you brush without paste, you'll remove the food particles. That's good, as it removes what feeds bacteria.  But without the paste, your teeth will most likely become yellow with tartar.  If you go to a dentist with yelow teeth, he'll most likely be a lot more agressive in treatment, as he'll have more to remove before he can spot any cracks ("leaking" as they call it) or decay.  And when he finds something, he'll go for the maximum corrective treatment, drilling & filling to the max, because he'll be thinking here's a dumb patient whose teeth are going to rot - whereas if you present with nice clean white teeth, he might be more likely to say "we need to watch that tooth, but it's ok until your next checkup", or maybe just do a little tiny acrylic fill.
 * It is difficult to find info on this on the internet that isn't likley to be commerically biased, or just mumbo jumbo. This is a good as any: www.dentalgentlecare.com/toothpaste.htm.
 * Wickwack121.215.159.205 (talk) 02:19, 4 September 2012 (UTC)


 * Wickwack, I appreciate your enthusiasm for the subject, but this is a very poor answer by Reference Desk standards. (1) You have not included a single reference except for your sideswipe at the end, a link to a few paragraphs written by some individual, non-notable dentist. (2) Factual inaccuracy.  Stating that the main function of brushing is dislodging food particles and rubbing the paste on the teeth is nonsense.  The main function is to remove biofilms that accumulate on the teeth because of the normal mouth flora.  This can be demonstrated in your own mouth quite simply.  (a) Brush your teeth and go to bed.  (b) Sleep, then wake up and run your tongue around your teeth, front and back.  Feel the texture.  (c) Brush your teeth with no toothpaste.  (d) Run your tongue around your teeth again.  Feel how they feel smooth and polished and clean?  That's not food particles that have been dislodged, and it's not the rubbing of paste on your teeth; it is the mechanical rubbing off of the biofilm that your mouth bacteria generates continuously.  (d) Your gratuitous blowing-off of the benefits of fluoride, despite our referenced articles like Fluoride therapy, shows you're one of those weird anti-fluoridation activists, which would be OK with me if you supplied references ... but you haven't.  (e) Your cynical note about dentists "drilling & filling to the max" because of yellow teeth is again nonsense.  (f) This is a little much to ask, but if you could apply some imagination, you might not blow off my percentages question quite as much ... not that this means much to be based on your obvious unfamiliarity with the subject.  (One alternative phrasing could have been something like "If two patients with similar mouths and dental activity were to be compared, one brushing with toothpaste and one brushing without, what would the differences be in their dental health, and by how much?")  Please do not post to the Reference Desk without references.  One reason is that it gives readers followup material; another is to reduce errors, like the many errors in this sad post of yours. Stingray Xray (talk) 16:46, 4 September 2012 (UTC)
 * Stingray, if you actually read what I wrote, you'd notice that I strongly AGREE with flouridation of water, and only regard mechanical application of flouride to teeth as probably useless. You'd also see that I gave a range of topics that any reader can follow up for themselves.  I fully agree with and support the need for references in Wiki articles, but this is Ref Desk.  Here, orginal research and even personal opinions are fine, provided they are constructive.  I note that personal opinions and anecdotes on Ref Desk are very common, from many contributors.  Just because a Wikipedia artcles said something is so doesn't make it right, and doesn't make it the last word.  It is Wikipedia policy, and a good one, that Wikipedia is of most value not because of the content per se, but because it gives readers topics and terminology to search on, and links to references.  Finally, if you don't like answers, then don't post questions - otherwise after a while you won't get any answers.  Wickwack121.215.159.205 (talk) 22:07, 4 September 2012 (UTC)

Fluoride benefits ?
As for the benefits of fluoride, I'm under the impression that the fluoride in toothpaste doesn't do you much good, while a fluoride treatment, on the other hand, seems quite beneficial in hardening the teeth and thus resisting cavities (this is where you hold "trays" on your teeth while the solution soaks into your teeth, similar to some whitening methods). This hardening might, however, make chipping more likely. Is this all true, and, if so, why ?

I know that fluoride in large quantities is poisonous, so that might explain the toothpaste part, if they put in too little to be effective in order to avoid toxicity (say if a toddler eats a tube of toothpaste). Perhaps they can risk more in a dentist's office, where the treatment is given, since you are under their supervision when that is used ? StuRat (talk) 02:50, 4 September 2012 (UTC)


 * I was under the impression that brushing without fluoride doesn't do much good, hmm, will need to look into it. The Toothpaste section doesn't really say either way. On a related note, municipal Fluoridation is certainly effective at reducing cavities in a population. Vespine (talk) 03:23, 4 September 2012 (UTC)


 * I'm not so sure. We seem to get plenty of cavities in areas which do this.  Do they just add too little, again to avoid potential toxicity ?  I also get the impression that the benefits of fluoride are not cumulative, so small doses which add up to one large dose do not give the same benefit as the one large dose.  Any truth to this ?  StuRat (talk) 03:36, 4 September 2012 (UTC)


 * This is now off topic, and it would take too much time to track down references. But here's my take on it, based on a combination of what I've read in newspapers and my own knowledge:-
 * 1. Putting flouride in toothpaste is just a marketing thing, with no actual benefit.  It's not so much about how much they can safely put in, it's about the chemistry of flourine
 * 2. While dentists may promote it, its something they can charge extra for, and some may actually believe in it, flouride treatment in the dentist's charir is useless for the same chemistry reasons.  My own dentist says it's a con.
 * 3. Some countries add flouride to the public water supply, as is done where I am (Western Australia).  The flourine from this does get into the teeth and confer a useful benefit, as the body has metabolic pathways that get around the chemistry.
 * It may be useful to go thru the history of flouride in water in W. Australia. In the 1950's and 1960's there was a huge Government campaign to get children to brush their teeth effectively, at least twice a day.  Advertising was directed at parents, we were taught proper brushing at primary school, nurses checked us at school, the works!  This was because, pre-World War 2, as in USA, Britain, and elsewhere, most folk had poor teeth hygiene, and also by middle age mostly had no teeth.  The market for false teeth was huge.  However, all those post-war children still got lots of cavities.  An investigation was done, which showed that the amount of flouride present naturally in West Australian water was much lower than in most European countries.  So, in about 1964, the State decided to add flouride to the water.  Sure enough, the next generation of children had far fewer cavities.
 * It follows from this, that if your area is like ours and has naturally low levels of flouride, then there is a marked benefit in adding it to public water. However, if your area already has lots of naturally occuring flouride, there is no need to add more.  I read somewhere that the amount added by certain USA states is about 1/3 or so what the West Aust Govt adds for this reason - these US states already have significant natural flouride, so they don't need to add so much.
 * Because tooth decay is casued by a certain type of bacteria, you can get the benefit of flouride without getting any flouride yourself! I grew up in a semi-rural area where the main comercial activities are chicken ranching, orcharding, and some mixed farming (goats, pigs, & whatnot).  The folk that live in the town are on the public water supply which is flouridated.  Sure enough, town children tooth decay rates dropped markedly when flouride in water started.  However, almost every farm, chicken ranch, orchard, or whatever, had and still have their own water supply - they are not on the town supply.  Decay rates dropped in farm-raised children as well!  Not quite as much, but almost as much.  Why?  Partly because when at high school, they drank the school water (on the town supply).  And partly because their town friends had low decay, leading to low bacteria load in their mouths.  Somehow the bacteria get from child to child (otherwise there wouldn't be any tooth decay bacteria).
 * In W Australia, tooth decay rates have been rising alarmingly in the last 10 years or so, in spite of flouride in the water. It is thought to be due to children drinking a lot more sugar softdrinks than before, and a lot less water (the McDonalds & Kentucky Fried effect  "Would you like a large Coke with that?").  It may also be that the bacteria have evolved in response to the high flouride, and we now have stronger bacteria.
 * If you make it to adulthood without cavities, mostly you'll be fine from then on (assuming you brush effectively etc), regardless of flouride levels. Flouride helps, but it's while you are growing that it really matters.
 * I mention all this because you hear/see a lot of rot on the pros & cons of flouride in water etc. Evidence may appear contary unless you understand all the factors.  Incidentally I grew up on a chicken ranch with no flouride in the water and went to school in a non-flouride area.  I'm in my 60's now and still have all my teeth.  Wickwack121.215.159.205 (talk) 04:55, 4 September 2012 (UTC)


 * What is the "chemistry" which prevents fluoride from hardening teeth when applied topically, but allows it to work when ingested ? I would have thought the reverse, as fluoride in the blood would only harden the teeth right around the root, while, if applied topically, it can harden the outside, where it's needed the most.  StuRat (talk) 17:35, 4 September 2012 (UTC)
 * Stu, when I was doing an Engineering degree at university decades ago, I did a couple of chemistry units, taught by a lecturer who was an expert on water quality in municipal water supplies, as well as a couple of other fields. We covered the chemistry of flourine, and I recall that the chemistry of flourine was against direct mechanical application, in fact we had an assignment question on it.  There has also been some info in consumer choice magazines in the years since.  However, not being a chemist I can't recite it all from memory.  If you would like to know, please ask in a separate question.  You may get some good responses from others, or you may not.  I will attempt to track down the info we had at Uni.  It's off topic, so I'm not going to spend time on it here on this question.  You will be aware than the body utilises a number of trace elements and other nutrients where activation energies in the chemistry works against it, but the body has evolved a range of complex enzymes & metabolic pathways to enable such elements etc to be used at the cost of some calories.  Wickwack121.215.159.205 (talk) 04:53, 5 September 2012 (UTC)


 * Again, you have not cited any references. This is the Reference Desk.  Please cite references.  Stingray Xray (talk) 16:49, 4 September 2012 (UTC)
 * You did not provide any usefull references in your rant above either. E.g., you cited a WP article on biofilms, but that has only one para on dental film (tartar/plaque) and it has nothing that supports your rant.  Wickwack121.215.159.205 (talk) 04:39, 5 September 2012 (UTC)


 * Fluoride effects the demineralization of teeth caused by organic acids produced by bacteria. It doesn't do anything to the bacteria themselves.
 * Trends in tooth decay decline were seen in countries that introduced water fluoridation, in countries that didn't have water fluoridation and in countries that stopped adding fluoride to drinking water.
 * Fluoride toothpaste is considered the main reason for tooth decay declines in industrialised countries.
 * On a different note: eating (hard) cheese after a meal reduces tooth decay because it helps the remineralization process. Ssscienccce (talk) 17:09, 4 September 2012 (UTC)
 * You get a ceratin bacteria load in your mouth anyway. Brushing with paste helps keep the bacteria load down.  However, if there is inadequate flouride in the food & drink you consume, you will get more tooth cavities. And the cavities will get larger before you or your dentist notices in your annual checkup, assuming you have annual checkups.  Cavities provide a more ideal home for bacteria than does the tooth surface, and brushing is ineefective at removing bateia from cavities.  Thus, low flouride DOES increase the bacteria load in you mouth, further increasing the decay problam and increasing the probability of you pasing the bacteria on to others.
 * Regarding trends, it may be that some countries continue to see a reduction in cavities. Because decay is caused by a specific bacteria type, there will be other factors.  However, in Australia, it is well documented that decay is rising again, despite flouridation.  This does not invalidate flouridation of public water supplies for the reasons I gave above (increased softdrink consumption, decreased tap water consumption, possible evolution of mouth bacteria) - in fact flouridation is thus more important now than it was before.  Wickwack121.215.159.205 (talk) 04:39, 5 September 2012 (UTC)

Also, I suspect that most bottled water is non-fluoridated, except for when it just contains tap water, leading to increased decay. Is this true ? StuRat (talk) 17:35, 4 September 2012 (UTC)
 * I can't speak for Stu's USA, but here in Australia, bottled water is essentially two types: (1) Water sourced from the public water supply and claimed to be filtered by the bottling companies.  This water will have the same flouride content as what comes out the tap. (2) expensive, premium brand / boutique "spring water" imported fron Italy and eslewhere.  I don't know what the flouride levels would be, but the cost limits its consumption to special occaisons, restaurants, and the like, so it won't matter much anyway.  Wickwack121.215.159.205 (talk) 04:39, 5 September 2012 (UTC)

Strontium also has some benefits for teeth. Count Iblis (talk) 22:31, 4 September 2012 (UTC)


 * To go really far afield on a favorite side-track [sorry :)] I'm thinking that the ancestral terrain in which humanity evolved should, on average, have the optimum level of natural fluoride in the water, or else we would have evolved a different preference. There is some population genetic evidence to suggest that humanity radiated out from the general region of Namibia (though personally I'm a fan of the Okavango Delta and larger regions which might have been similar millions of years ago...).  I should note that at least one town in Namibia, Otjiwarongo, is noted in the literature for people with minor fluorosis due to natural fluoride concentrations of twice the usual recommended level.   So I think that fluoride in water can indeed be viewed as a true supplement, not a sinister drug conspiracy, though of course the infrastructure might be usable ..... Wnt (talk) 02:08, 5 September 2012 (UTC)
 * Exactly. Your statement is in accordance with what they State Govt told us when they started flouridation of water.  Our water happens to have very low natural flouride levels, so adding it was a benefit.  Other countries which have naturally high flouride levels meeting or exceeding the body's needs don't need to add it.  Wickwack121.215.159.205 (talk) 04:21, 5 September 2012 (UTC)


 * My earlier post might be a bit out of date. I recall that some years ago, manufacturers of toothpaste in their marketing and packaging were quite heavily promoting that they included a flouride in their product.  However, I have just done my weekly shopping and took the opportunity to look at the various brands & types of toothpaste on display.  The shop had 6 different brands and over 20 different types.  Some of the brands are actually made by a common manufacturer. The major brand Colgate has 5 different types, and only one type has "sodium flouride" listed, in the ingredients fine print.  One brand had sodium flouride listed in fine print of all 4 of its types. All other brands made no mention of flouride at all.  None of the toothpaste displayed any claim that they could reduce decay, cavities, or incidence of cavities.  An interesting side issue:  some brands having more than one type of paste, identified by different names (eg "Total Protection", "For Sensitive Gums", & the like, actually had the same ingredients and quantities listed in the ingredients fineprint.  Wickwack121.221.223.160 (talk) 06:31, 8 September 2012 (UTC)

Are disabled and mentally-handicapped people self-aware?
And by self-aware, I generally mean able to pass the mirror test. Futurist110 (talk) 03:42, 4 September 2012 (UTC)
 * Just a wild guess, but I think Stephen Hawking would pass. Clarityfiend (talk) 05:00, 4 September 2012 (UTC)
 * What about people with Down syndrome or other severe mental impairments? Hawking's impairment is more physical--he is extremely intelligent mentally. Futurist110 (talk) 05:07, 4 September 2012 (UTC)
 * I think you might want to try being a little more specific than "disabled", as I am somewhat confident that most paraplegics, amputees, and hearing-impaired people would pass the mirror test just fine. That said, I believe the age threshold for humans to pass the mirror test is around a year old or so, so any mentally handicapped person with a "mental age" over 12 months should be able to pass it as well. This would include the majority of those with Down syndrome. Evanh2008 (talk&#124;contribs) 05:11, 4 September 2012 (UTC)
 * That's a simplistic view of mental age, and even if you could measure mental age below 1 year, I'm not sure it'll tell you much about the mirror test. In Phantoms in the Brain, the author Ramachandran describes a hemispatial neglect patient who seemed like a perfectly intelligent elderly woman in every way.  Since she was neglecting her left field of vision, the author put a mirror in front of her so that her left side would seem appear in her right field of vision, and wondered how she'd react.  She reached into the mirror to grab an object she saw in the mirror, and proceeded to complain that she couldn't get it because the mirror was in the way!  Even a chimp can figure out how a mirror works, yet here was a perfectly intelligent woman who somehow couldn't understand the difference between a physical object and its reflection.  --99.227.95.108 (talk) 06:04, 4 September 2012 (UTC)
 * Also, I agree that the answer to the OP's question depends heavily on how mentally-handicapped you're talking about. If you have anencephaly, there's no way you're even conscious, let alone self-aware.  On the other hand, I am mentally handicapped (I have Asperger's syndrome), but I'm pretty sure I'm self-aware... --99.227.95.108 (talk) 06:11, 4 September 2012 (UTC)
 * Have you ever met somebody with Down syndrome? They obviously are self-aware (unless they have other much more serious impairments). Staecker (talk) 16:27, 4 September 2012 (UTC)
 * Not in real life, No. Futurist110 (talk) 18:29, 4 September 2012 (UTC)
 * If you've actually never met anyone with Down syndrome, you must have led a very sheltered life. I suspect that it is much more likely that you have, but weren't aware of the fact. AndyTheGrump (talk) 18:40, 4 September 2012 (UTC)
 * I've seen such people in passing and exchanged a few words, but not interacted enough to answer such questions with confidence. And the degree of impairment appears to vary widely. —Tamfang (talk) 21:52, 4 September 2012 (UTC)


 * You may wish to read Oliver Sacks's "The Man who Mistook his Wife for a Hat" for some insight into the tricks our brains can play on us once damaged. --TammyMoet (talk) 10:03, 4 September 2012 (UTC)
 * I'll also link you to the story of an old neighbour of mine: Sharon Parker. --TammyMoet (talk) 10:06, 4 September 2012 (UTC)

Our OP may benefit from watching the Paralympic Games currently under way. These Games signal the return of intellectually disabled athletes to the Games after it was discovered at the 2002 Sydney Games that some of them were just a bit too smart. HiLo48 (talk) 05:58, 5 September 2012 (UTC)

Rigid pavement
In rigid pavement design we use a variable with a unit of length which we call "radius of relative stiffness".Why we call it radius?With which circle is it related? — Preceding unsigned comment added by 116.90.230.202 (talk) 09:33, 4 September 2012 (UTC)


 * Searching around, I discovered that one Dr H. M. Westergaard  is responsible for the name of the variable, and that this is the same Westergaard who invented a thing called the Haigh–Westergaard stress space, along with somebody called B. T. Haigh . Beyond that, I'm guessing. I notice that the "stress space" maps three different kinds of stress (I don't know what they are) to the three spatial axes (up-down, left-right, forward-backward), so this might explain why an apparently spatial idea (radius) is being used in a context where it doesn't seem to apply: the circle is probably, in some sense, a circle of stress. Not a circle in ordinary space.  Card Zero  (talk) 12:29, 4 September 2012 (UTC)


 * It's measure of the stiffness of the slab relative to the stiffness of the subgrade. A measure of how much a load on a small area of the slab is distributed over a larger area of the subgrade. For example, take a thin slab on a subgrade of solid granite rock; the rock won't deform at all, so the total weight of a load would be carried by the area directly under the load and the "radius of relative stiffness" would be zero. The other extreme would be a concrete slab on an air cushion where the force is evenly distributed over the total area, regardless of the size of the slab. Its called radius because a point load will be distributed evenly in all directions, ie two points at equal distance from the load will experience the same force.  Ssscienccce (talk) 19:29, 4 September 2012 (UTC)

Machining
What is grinding wheel signature? — Preceding unsigned comment added by Syed raziuddin (talk • contribs) 15:22, 4 September 2012 (UTC)


 * The characteristic pattern left by a particular grinding wheel? If I were to hazard a guess, that would be what I would think. -- Jayron  32  16:20, 4 September 2012 (UTC)


 * Depending on the context, this could also mean it's vibration profile/acoustic signature (unfortunately, our article is limited in scope to the naval usage). That is, the specific sound it makes.  Analyzing changes in the sound can detect problems, like an imbalance, before they are otherwise obvious. StuRat (talk) 19:33, 4 September 2012 (UTC)

Breaking down hardened building cement or concrete
I am an electrician based in South Africa and have a problem with building cement that has dried inside an electrical conduit. Is there perhaps an acid or some sort of solvent that will either breakdown or dissolve the cement? 41.13.60.104 (talk) 17:23, 4 September 2012 (UTC)


 * Yes. Specifically, if the concrete contains lime, a strong acid should eventually dissolve it.  But it's hard to imagine something that wouldn't also do damage to electrical conduit, any wires in it, and, by leaking out, the rest of the structure.  If the conduit is completely blocked off, you would also have the problem of delivering the acid.  And, if you did manage to dissolve the lime component, you would still be left with conduit full of sand, gravel, and acid.  I really don't think this approach will work.  Unfortunately, I'd say you need to abandon all hope of using that electrical conduit.  You can either remove it and replace it, or, if this is impossible at this point, then leave it in place, but don't use it (if you do use wires already inside it, they are likely to overheat, as the concrete will act as thermal insulation).  Just add new conduit.  If the wall is entirely filled with concrete, you will need to drill a path for the new conduit.  Cement filled walls are a bad idea exactly because of the problem of changing wiring or plumbing after it sets.  StuRat (talk) 19:29, 4 September 2012 (UTC)


 * Lets get things into context. You are an electrician. So, can I take it you where not the one pouring concrete into places it was not supposed to go? Therefore, you should inform your supervisor that who ever poured the concrete have neglected their 'due care' and therefore are obligated to come back with their high pressure jet (of about 2,000 psi) and blast it off.  Concreting companies   should have this equipment because concrete will get stuck to a lot of their equipment so they need this type of gear. As StuRat has stated, there are many acids that will also remove set concrete. However, should your supervisor be week-knead and too shy to make a fuss and be looking towards 'you' for an answerer, then there are acid based mixers that are formulated for this sort of problem. Get on the works phone (i.e.,  let them pay for the call) and talk to a reputable company's  'technical department'. The sort of formulations you should enquire about is something based on something like glycolic acid. See for example:  Refrain from using this stuff to clean antique marble fireplaces etc., - not wise. --Aspro (talk) 22:37, 4 September 2012 (UTC)


 * Only very patient bakers should attempt a week-knead. :-) StuRat (talk) 22:44, 4 September 2012 (UTC)
 * And the boy gets a cigar! ←Baseball Bugs What's up, Doc? carrots→ 03:04, 5 September 2012 (UTC)


 * Without elaborating at all, I see you guys don't understand the challenges of the building "industry" in South Africa. Applying North American (or whichever) standards to (South) Africa is like trying to introduce advanced engineering to a pre-schooler. Best of luck, Mr. Electrician ;) Sandman30s (talk) 13:08, 5 September 2012 (UTC)


 * While there are parts of Africa which lack industry, the nation of South Africa is not among them. See Economy of South Africa. StuRat (talk) 21:27, 5 September 2012 (UTC)
 * Doesn't matter what that article or any official document says. My comment is from first-hand experience with builders, and from the experience of many others. Sure, there might be an end point but the path to the end is fraught with maladies like what the OP describes. And at the end, unless you are rich enough to have used one of the stock-exchange listed development companies, your product will be lacking in quality to say the least. Sandman30s (talk) 11:47, 6 September 2012 (UTC)
 * Various practical solutions depend on the scale (sorry:) of the situation. Partial vs total blockage, length and diameter of the problem, accessibility of it (the conduit tube itself in that area and the position of that area from an open end). DMacks (talk) 11:52, 6 September 2012 (UTC)

self combustion
What's the difference between spontaneous combustion and pyrophoricity?--Jsjsjs1111 (talk) 17:29, 4 September 2012 (UTC)


 * There might be some overlap, but I'm under the impression that "spontaneous combustion" typically refers to things that slowly heat to combustion temperature, like oil and gasoline soaked rags in a pile, versus pyrophoricity referring to things which ignite immediately in air and/or water. StuRat (talk) 19:23, 4 September 2012 (UTC)
 * Definitions seem to vary depending on source. The DOE Handbook Primer on Spontaneous Heating and Pyrophoricity seems to use spontaneous combustion as the general term, saying it is the ignition of a combustible material caused by the accumulation of heat from oxidation reactions. Adding: fires started by spontaneous combustion are caused by the following mechanisms:
 * spontaneous heating (what wikipedia calls spontaneous combustion)
 * pyrophoricity: Pyrophoric substances ignite instantly upon exposure to air (atmospheric oxygen). This is a special case of a hypergolic reaction with the oxidizing agent restricted to atmospheric oxygen.
 * hypergolic reaction: material's ability to spontaneously ignite or explode upon contact with any oxidizing agent.
 * There have been a few spectacular examples of spontaneous heating of ammonium nitrate cargo, destroying ship, harbour and town in one massive explosion. Ssscienccce (talk) 18:39, 7 September 2012 (UTC)

What´s happen if we put a reference system in a photon ?
I´m trying to understand some concepts of quantum physics and I was thinking about time and space contraction. I´ve understood from articles that when particles take speeds near light speed, for observers that are in other referencial system, as in Earth for example, we have time dilation, so for referential system in a photon it should be a time and space contraction. If some particles takes speed as v=0,999999c, the contraction factor it should be 707. If speed of particles are 0,999999999999 c so space contractios it should be around 707107. So, as close we get from light speed, higher it will be the contraction. So whats happens to photon ? If we think in a referential system linked to photon, whats happen with time and space contractions ? May I think that in a photon speed, the time intervals compared with earth time, are so small that it will not take time to go from a point to another and, based of this photon can occupy several places in a space in same time ? Please help to understand this situation! — Preceding unsigned comment added by Futurengineer (talk • contribs) 17:45, 4 September 2012 (UTC)


 * There are two common answers to this that I have heard:
 * This is a meaningless question; photons don't really have meaningful reference frames.
 * You could imagine the photon's reference frame (still not a real thing) as being one where both time and space were infinitely contracted (that is, time is stopped and space is nothing).
 * The former is probably correct but boring; the latter is interesting but probably wrong. Take your pick! At least until someone with more physics chops shows up. (You might also be interested in the idea of the one-electron universe.) --Mr.98 (talk) 18:10, 4 September 2012 (UTC)


 * Mr 98's answer pretty much hit the target. The photon's reference frame is not a valid reference frame because it gives a infinite Lorentz factor. Another way to see that problem is that in this pseudo-referential the photon would be at rest, but that contradicts the principle of invariant light speed, one of the postulates of special relativity. Also, there is no possible Lorentz transformation that would lead into such a pseudo-referential so it is not an element of Lorentz group. Dauto (talk) 00:31, 5 September 2012 (UTC)
 * Great minds think alike, Futurengineer. From Einstein's Autobiographical Notes, "...a paradox upon which I had already hit at the age of sixteen: If I pursue a beam of light with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as an electromagnetic field at rest though spatially oscillating. There seems to be no such thing, however, neither on the basis of experience nor according to Maxwell's equations. From the very beginning it appeared to me intuitively clear that, judged from the standpoint of such an observer, everything would have to happen according to the same laws as for an observer who, relative to the earth, was at rest. For how should the first observer know or be able to determine, that he is in a state of fast uniform motion? One sees in this paradox the germ of the special relativity theory is already contained." See and John Z (talk) 14:08, 5 September 2012 (UTC)

] Thanks everybody, I´m just wandering how explain that light(photons) goes for several paths before we measure that. Also, the spin of one electron seems to be linked to other in such way that if we change spin of one, the other change in same instant. And also we know that there is no actual vacuum in space but a sea of bosons. So, how understand this? It seems that the universe from perspective from elementary particles like photons could be different. That is why I was try to open my mind for news perspectives. — Preceding unsigned comment added by 187.64.171.240 (talk) 17:35, 5 September 2012 (UTC)
 * Regarding the problem of the linking of spins of fundemental particles, see Quantum entanglement. One's persective on quantum entanglement, that is, whether it is a sort of "no DUH?" kinda unsurprising fact which is expected, or whether it is some weird, unexpected, and odd occurance (called "spooky action at a distance" by Einstein et. al.), depends on which particular Interpretations of quantum mechanics you ascribe to.  -- Jayron  32  17:42, 5 September 2012 (UTC)

Calorie-equivalent exercise compared to wading in a pool.
I'd like to know a range of how many calories per distance (or time, but distance is better) would be burned by wading in a pool filled to should(er) depth, and what sorts of activities would burn close to the same number of calories for the same person. In otherwords, I want proportional numbers, not absolute numbers. I have looked but we don't seem to have anywhere near a list of calories burned by activity. Thanks. μηδείς (talk) 18:42, 4 September 2012 (UTC)


 * Let me shoulder the burden of asking if "should" should be "shoulder". :-) StuRat (talk) 19:20, 4 September 2012 (UTC)
 * Look, I don't type these things. My fingers do. μηδείς (talk) 19:22, 4 September 2012 (UTC)


 * It will depend entirely on water temperature. In tepid water, you might as well be lying in bed.  In cold water, you can burn a significant number of calories.  And of course the more you move around, the more calories you will burn. Looie496 (talk) 22:12, 4 September 2012 (UTC)


 * I disagree with "In tepid water, you might as well be lying in bed". Wading through shoulder-deep water at a high speed takes a considerable effort, owing to the much higher density of water than air. StuRat (talk) 23:19, 4 September 2012 (UTC)


 * Medeis didn't say anything about high speed. Looie496 (talk) 00:13, 5 September 2012 (UTC)


 * I didn't want an argument, but a ref to a website with a list of calories for each exercise type. Assume 80 degrees F, although I though the resistence would be what matters.  I meant at the highest speed one could go, that's usual for calorie-burning exorcises. μηδείς (talk) 01:06, 5 September 2012 (UTC)


 * And wading in shoulder-depth water still takes more effort, at any speed, than lying in bed. StuRat (talk) 20:24, 7 September 2012 (UTC)


 * Maybe what you want is here? Mayo Clinic is an authoritative organisation and I'd have thought this would be reasonably accurate. --TammyMoet (talk) 14:16, 5 September 2012 (UTC)


 * Yes, that's excellent, exactly the sort of thing I was looking for, although it doesn't give info for wading. Subjectively I think the 10mph bicycling would be about the closest in effort. μηδείς (talk) 17:18, 5 September 2012 (UTC)
 * Our article Water aerobics could do with some more development! Graeme Bartlett (talk) 09:36, 6 September 2012 (UTC)

Does nioxin shampoo make hair grow?
Currently most of my hair is shoulder length and the on my hair is jaw-length out grown bangs. How many faster would nioxin shampoo make it grow? Neptunekh2 (talk) 19:34, 4 September 2012 (UTC)


 * Comment: The Nioxin article looks a good contender for AfD - spam.--Aspro (talk) 19:41, 4 September 2012 (UTC)
 * [removed stray template] μηδείς (talk) 01:10, 5 September 2012 (UTC)
 * I can still see the question ! And the professional is called a trichologist. An'  still think the article  should be AfD'd.--Aspro (talk) 22:43, 4 September 2012 (UTC)
 * I suspect Nioxin is notable enough for an article. The existing article does look like an advertisement, but that's cleanup, not deletion. --Trovatore (talk) 23:20, 4 September 2012 (UTC)
 * The answer to the question is no; even the manufacturers don't claim it will make hair grow. As for the article, it desperately needs reliable sources, and the squishing of the spam links.--Shantavira|feed me 12:12, 5 September 2012 (UTC)

Mind downloading
Would it eventually be possible to download's one entire mind into a virtual world? One of my friends made this proposal as a possible future response to severe overpopulation caused by a cure to aging. Futurist110 (talk) 22:07, 4 September 2012 (UTC)


 * Please review WP:CRYSTAL, and ask yourself how you think any of us might answer your question. AlexTiefling (talk) 22:08, 4 September 2012 (UTC)


 * We actually have an article on Mind uploading. Beyond pointing you to that article, the best answer anyone can give you is, "Maybe?" No one can provide accurate predictions about future technologies when we don't even understand the science that it relies on. Someguy1221 (talk) 22:12, 4 September 2012 (UTC)


 * It'll be SOP if the excellent Iain Banks is a futurologist and not an SF writer in desperate need of a technology to make galactic exploration practical. Bandwidth and storage wise it doesn't seem ridiculous, but the whole brain scanning part is still in its, well not even infancy, more like we have some sort of vague idea how memory works. The other bit is philosophical, if I make an exact copy of my mind, and boot it, and kill the original, is the new one 'me', or just a copy? My gut feel is that copies will feel like they are me, initially, but killing 'me' to make a copy is still dying. Greglocock (talk) 03:06, 5 September 2012 (UTC)


 * That issue can be addressed by not booting up until you die naturally. If we can do a scan of your brain each night as you sleep, and update the copy accordingly, then you would lose, at most, one day's worth of memories when you die.  If you suffer from dementia, though, we might want to go back to a "checkpoint" taken before the dementia started. StuRat (talk) 03:18, 5 September 2012 (UTC)


 * This is purely my own opinion unreferenced here, so I hope Medeis doesn't hop and delete the thread, but I would personally be more comfortable if you simply blurred the distinction between mind and machine. Upload your brain to a machine that is built into your brain, constantly updating, and "assisting" you. As your brain naturally decays with age, the machine takes over more and more functions, eventually becoming your entire mind. This way there is no single moment when you stop being you and start being a machine. Then again, we still can't explain the experience of consciousness, or even know if it has a true scientific basis, so all my method accomplishes is making me feel better. Someguy1221 (talk) 03:24, 5 September 2012 (UTC)
 * "Eventually"? Why do you think this hasn't been done already, that you aren't there already? Didn't you get the How2getouttahere pamphlet at the entrance? Me, I'm going Back to Reality (Red Dwarf).John Z (talk) 13:52, 5 September 2012 (UTC)


 * As an alternative to activating a "last good version" (whose definition is nontrivial!), I've thought of wiring all available backups together, thus: each neuron, instead of connecting to other neurons in its own "slice", connects to the corresponding neurons in both adjacent slices. Knowledge acquired during the declining stage can then propagate to, and be processed by, the healthier versions.  A big problem remains: where to connect the i/o ? —Tamfang (talk) 06:15, 6 September 2012 (UTC)

You are your body. Your consciousness is a harmonic relationship between your body and its environment, like a hum in tuning fork induced by an outside vibration. The simple answer is no. Copy the hum of a tuning fork onto a tape and destroy the fork then you are simply dead and playing the tape is a simulation, however self-satisfied it is and however comforting to others. But Someguy has it right. You are your body. If you can slowly replace parts of your body, whether by generating new cells, or replacing them with machine parts, without disrupting the major continuity of your consciousness, then you can have your actual immortality, rather than making a realistic Tupac hologram of yourself. PS. If I am missing a good reason for hatting this thread, let me know, and I will get on it right away. μηδείς (talk) 18:46, 5 September 2012 (UTC)


 * See Ship of Theseus. StuRat (talk) 21:24, 5 September 2012 (UTC)


 * One definition of 'me' is my living body. Another reasonable definition is my behavior.  The thing that bothers me most about death (other than the unpleasantness of the transition) is that with me gone no one will do the things I intend to do.  A software copy of me will have the same tastes, and therefore will carry on my projects, whether or not it is me in your philosophy. — I still prefer incremental prosthesis, though. —Tamfang (talk) 06:15, 6 September 2012 (UTC)


 * The phrase "my behavior" amounts to begging the question. An entity is its attributes.  That includes the sum of its properties, states, qualities, actions, relationships, etc.  The word "my" in my behavior stands in for "the behavior of this body".  It is only the behavior of that body if it is the behavior of that body.  Unless you are looking at behavior as an alienable, rather than inalienable possession.  As in, I paid that hooker to pole dance, so that's my behavior she is doing.  Or, "Look, dear, the mime is doing such a great impression of your walk!"  If that's the case, Elvis is alive today...in each one of his impersonators.  μηδείς (talk) 07:34, 6 September 2012 (UTC)


 * Only if they are exact replicas, which they are not. StuRat (talk) 10:29, 6 September 2012 (UTC)


 * If you were standing next to your exact replica, Stu, would his thoughts be your thoughts? μηδείς (talk) 01:24, 8 September 2012 (UTC)


 * No. First, the environment is never exactly the same.  Even if they always stood next to each other, each person would experience a slightly different view, sounds, etc. (would the one on the left turn out to be a leftist ?). :-)


 * Then there's also a random factor involved. Even identical twins don't have identical freckle patterns.  Similarly, sometimes one twin is straight and one is gay, even when raised together.  So, something random is clearly going on in the brain, too. StuRat (talk) 02:29, 8 September 2012 (UTC)


 * Medeis, I can play your game too: "my body" really means "the body occupied by a person who behaves as I do".
 * If I wrote some programs in 2002, copied them to another computer in 2005 and then to yet another computer in 2010, should I consider them new programs and the old ones lost?
 * If "an entity is its attributes", does someone die with every transfer of property? Change of clothing?  Haircut?  Tooth extraction?  Amputation of a digit?
 * If an Elvis-impersonator could accurately reproduce all the behavior of the real Elvis – not only aping his stage mannerisms but sharing his memories and opinions (which are learned acts of thought) – I'd consider him functionally equivalent to a real living Elvis. We don't yet have good vocabulary for what I really mean, so I'm forced to speak of behavior that matches the reference standard defined by the occupant of Elvis's original body.
 * I believe that my view will have a selective advantage over yours, but I don't say you're wrong; I similarly refuse to say the ancients were wrong in defining stars to mean "little lights in the night sky" (and thus to include the planets). —Tamfang (talk) 04:24, 8 September 2012 (UTC)


 * To ignore the undertones of that post, and simply answer your objections, saying that there is such a thing as your self prior to your bodies' existence, and that your body is identified as you only because it acts like that self, is begging the question. It sounds like the mystical Tibetan Buddhist process of identifying lamas, or some weird scifi premise.  Or it would be like if the word Google had always existed, and people had always wondered when it would be invented, and the one day Larry Page turned to Sergey Brin, and said, "Oh my God!  You know what?  I think we have finally invented the Google!"  The notion of self depends on the notion of a body, without which we could never have arrived at the concept of self.


 * As for the program, depends on the context which determines what definition you are using. If you are referring to the algorithm as such, it is the same.  If you are referring to its instantiation, then you have a physical replica which can perform the same function as the original.  But the replica is obviously not the original, just able to function in its place.  That's really not confusing.  People might not notice the original was destroyed.  Same as if it were possible to make a copy of you.  If I did that and then deleted you, you would still be have died, whether or not people knew the replacement was a copy.


 * As for "an entity is its attributes" that doesn't just mean at one moment. It is the sum of all of them through time. (By the way, there have been people who argue that an entity can be separated from its attributes--see transubstantiation.) Obviously if you have only lost your arm in a car accident, you haven't died. You have simply changed into a person who now lacks an arm. Neither do you cease being a person who once had an arm.  You have to understand that my point is not to say what science will or will not accomplish in the future, but to argue that a lot of confused ideas result from treating what are relations as if they were chemical substances.  You can't distill the mind out of a person and pour it into another container any more than you could distill the evil out of a murderer or an illegal drug and inject the evil into someone else, or remove a shadow from one body and attach it to another.


 * This was all discussed at length recently here: Reference desk/Archives/Science/2012 August 24 I suggest you read that thread, and take a look especially at two books I recommended that most libraries will have or can easily get, Introduction to Objectivist Epistemology, and Ten Philosophical Mistakes. Links to them at Amazon are in the old thread. μηδείς (talk) 17:19, 8 September 2012 (UTC)


 * Who said anything remotely like "there is such a thing as your self prior to your bodies' existence"? To generate a human personality requires a human body, yes; and to generate an orange requires an orange tree, but an orange doesn't cease to be an orange when you pick it.  (I know the metaphor is flawed. Not gonna spend all day looking for a better one.)
 * How sure are you that "we could never have arrived at the concept of self" if we had permanent personalities but not permanent bodies? I have no sure knowledge that any of the entities that post here (with one exception!) even has a body – some of you may be committees or programs for all I know – and yet I detect features of personality in some.
 * When mind-copying technology comes along, I believe we'll generally be better off if the law treats the vessel of a transferred mind as mostly equivalent to the original than if the body is the only legal entity. If you choose to see such transfer as a legal fiction, and insist that a copy of your dead friend is not your friend, I won't pressure you to socialize with Pseudo-Friend.  But personalities who accept copying will eventually outnumber those who don't!
 * Tangent: Your crack about the word Google reminds me of a conversation long ago. An entity that I'll call James advocated realism, which he defined as the position that meaningful concepts exist prior to our perceiving and naming them, and condemned nominalism, the practice of assigning words to arbitrary incoherent concepts.  I argued that with imperfect knowledge the best we can do is evolutionary nominalism, and James called my position realism. —Tamfang (talk) 02:16, 9 September 2012 (UTC)


 * Greg Egan's story "The Safe-Deposit Box" is narrated by a personality who (involuntarily) inhabits a different body every day. —Tamfang (talk) 06:42, 20 September 2014 (UTC)

Yet another bug ID question
The other day, in my yard in North Carolina, I spotted a rather large bee or bee-like insect (may have been a wasp or hornet, but it looked more bee-like to my untrained eye). It was unusually large for such an insect, and the coloration struck me. The main color of the head and thorax was a rusty brownish-red color, almost exactly like iron rust, while the abdomen was bright yellow striped, like a honey bee or yellow jacket. It was, however, considerably larger than either of those, perhaps twice the size of a typical honey bee. Anyone have a good guess as to what that might have been? I tried to snap a picture, but my phone camera's kinda sketchy, and I didn't get anything as it would move away by the time I could get it in frame. Doing some digging, the closest I could find was Sphecius grandis, but it wasn't quite that big (I don't think) and that species isn't known in this area. Any ideas on something kinda like that one but found in North Carolina? -- Jayron  32  22:20, 4 September 2012 (UTC)
 * My usual ref-desk answer to "bee-like insect" questions has been "some sort of hoverfly". There are so many species of the critters, however, that pinning down the exact one may be difficult. Googling for "North Carolina" syrphid will lead you to a lot of photos of various species; perhaps you can find one that resembles your sighting. Deor (talk) 01:02, 5 September 2012 (UTC)
 * Can you not upload a picture, Jayron? μηδείς (talk) 01:18, 5 September 2012 (UTC)
 * As I explained, I would have liked to, but I couldn't get him to sit still long enough to get one in my crappy flip-phone camera. The shutter response time was so slow that by the time I got him in frame and pushed the button, he'd moved out of frame.  -- Jayron  32  03:53, 5 September 2012 (UTC)
 * Doing some more research, I think it might be some species of Polistinae (paper wasp) that I hadn't seen before. We've got more species of wasp around here than you can shake a stick at; on any given day if I look I can find half a dozen or more different ones in my yard.  Though I've never seen one like this before (the rust color was rather striking), and though I can't find the exact one in any pics I have found, given the number and variety of wasps out there, I am thinking more and more that this is one of those.  -- Jayron  32  04:07, 5 September 2012 (UTC)

Can runners prevent knee pain by injecting motor oil in their knees?
You need to refresh the oil in your car, so why not do the same with our knees? Almost no runners who have been doing long distance running for more than a few year are completely pain free. Count Iblis (talk) 22:26, 4 September 2012 (UTC)


 * I very much doubt it. However, if you're contemplating doing something like that, talk to your doctor first. ←Baseball Bugs What's up, Doc? carrots→ 22:35, 4 September 2012 (UTC)


 * Motor oil is toxic. You are not even allowed to empty it down the drain because it is poisonous, it must be disposed of properly. The only thing you would gain by injecting yourself with it is an entry in the Darwin Awards. Try feeding your car by sticking a hamburger and chips into the petrol tank and then topping up with a large coffee with a few spoons of sugar. Your car wouldn't like it any more than you'd appreciate drinking a cup of petrol. Dmcq (talk) 22:47, 4 September 2012 (UTC)


 * I would argue that it could reduce knee pain, since you will soon be dead and thus unable to feel pain. StuRat (talk) 22:53, 4 September 2012 (UTC)


 * Silly question; See Synovial fluid. The omega fatty acids in the oil obtained from the Chinese Water Snake have been found of use in joint conditions based on generations of  empirical experience. However,  merchants of patten  medicine have regarded this treatment as  a competitious  threat to their lively hood and so have successfully hood winked the public into regarding it as   'snake oil'   which of course it is. --Aspro (talk) 23:14, 4 September 2012 (UTC)
 * Whether people have been using something for a long time says nothing about its actual efficacy; it could still just be placebo. (The placebo effect is still an effect, mind you. It's not synonymous with saying something is totally made up.) Show me some controlled studies that show it is better than mineral oil or just water and then we can talk like informed people. :-) --Mr.98 (talk) 13:05, 5 September 2012 (UTC)
 * A lot of work has now been done on eicosapentaenoic acid matched against placebo, both topical and oral, and so its been  known how snake oil works for the passed few decades. Having so many indications it would be better I think if you pick one out for yourself. This is not a chat-room. --Aspro (talk) 20:09, 5 September 2012 (UTC)
 * Just found what what claims to be the earliest  analysis of snake oil. . Hope this helps.--Aspro (talk) 20:18, 5 September 2012 (UTC)
 * I'm not interested in what's in snake oil — I'm interested in whether topical application is actually effective. If it actually is effective, add some real citations to the snake oil article or the Chinese Water Snake article. If the citations are so plentiful, you shouldn't have any trouble doing such a thing, no? --Mr.98 (talk) 18:05, 6 September 2012 (UTC)
 * You appear to be adopting the habits of an armchair pseudoskeptic that wants to be spoon-fed. I'm  not going to encourage this habit any further. As I said, this is not a chat -room  and you'll probably battle to have  the last word without adding anything useful to the OP's (silly?) question. --Aspro (talk) 18:56, 6 September 2012 (UTC)
 * Some good answers above. Note that as this is biology, we really don't know until someone injects his knees with motor oil, which means that hopefully this will remain an open question for a long time coming.  I don't know how quickly a hydrophobic liquid would leach out of the synovial space, but I'm thinking that longer term effects of injecting a solvent (but not short term effects like asphyxiation) would be comparable to huffing the same amount as a volatilized gas, which for anything but the smallest injection would be substantial.  I'm not sure if this is comparable to injuries from hydraulic fluid injection (which alas does happen with some frequency) - that can net a litigant $250,000 in damages. [www.sansonelaw.com/2012/04/250000-00-settlement-hydraulic-fluid-injection-injury-resulting-negligent-hose-repair/] Wnt (talk) 23:33, 4 September 2012 (UTC)

You now better than this, Iblis, and enough fun already. μηδείς (talk) 01:17, 5 September 2012 (UTC)


 * Well, as Ford Prefect never said, science is fun, so fun is science... :) Really though, it's a pretty straightforward thought experiment, and if we focused less on the toxicity and more on the mechanics someone might enlighten us greatly about how knees work. Wnt (talk) 02:13, 5 September 2012 (UTC)


 * It's a question, not a request for medical advice. So, what about other fluids that are not toxic? Count Iblis (talk) 01:38, 5 September 2012 (UTC)


 * Even water on the knee is not good. ←Baseball Bugs What's up, Doc? carrots→ 01:58, 5 September 2012 (UTC)


 * But then the body does use lubricants, so why can't we produce something that does work and inject that into the joints? Count Iblis (talk) 02:05, 5 September 2012 (UTC)


 * This is done - search for "synthetic joint fluid" and you'll find many doctors' sites. (Someone should start an article...)  One is Synvisc (that redirects to hyaluronic acid, which is scarcely deserving of being called such).  But glancing over the sites, apparently the stuff, while it might allow for reduced inflammation, still is mostly a weekly injection to delay harsher measures. Wnt (talk) 02:20, 5 September 2012 (UTC)


 * I've also heard of injecting chicken fat - again, a temporary measure. But that's a substance rather more likely to be compatible with an organism than refined petroleum would be. ←Baseball Bugs What's up, Doc? carrots→ 02:39, 5 September 2012 (UTC)


 * Well, any animal product adds the possibility of infection, as we would be vulnerable to many diseases normally wiped out by our digestive system when we eat them. While motor oil is toxic, perhaps some version of petroleum jelly could be used.  This is, after all, designed to be applied to the skin, so is non-toxic.  However, it might still create problems if injected. StuRat (talk) 02:51, 5 September 2012 (UTC)


 * I should clarify that this was some kind of "purified" substance that was administered under a doctor's care. And nobody should be injecting themselves with anything unless they're doing it under a doctor's care. ←Baseball Bugs What's up, Doc? carrots→ 03:02, 5 September 2012 (UTC)

Ultimately, while the quality of one's synovial fluid is strongly correlated with the health of the joint, the reduction in quality is merely a symptom. Various injections may reduce pain and inflammation, but it won't help the joint beyond that. As for motor oil itself, even if you ignore the fact that it's a terrible idea, it's also a terrible lubricant compared to synovial fluid, not even to mention they are used in different contexts. The coefficient of friction inside a human joint is on the order of 10 times smaller than what you find in lubricated machine parts (see here and here). I suspect this is why the stuff that doctors (quacks and otherwise) use as synthetic synovial fluid is either a synthetic compound or something derived from an animal. And indeed, there are plenty of sites advertising this type of procedure. Someguy1221 (talk) 02:57, 5 September 2012 (UTC)


 * This article on Runner's Knee (Patellofemoral Pain) suggests a variety of causes, none of which is a lack of synovial fluid. BTW, I've been running (admittedly fairly moderately, but I've done two full and many half marathons) since the 1970s and don't have any knee problems at all, unlike a lot of soccer and rugby players that I know. Alansplodge (talk) 14:13, 5 September 2012 (UTC)


 * Great question. Span (talk) 18:56, 7 September 2012 (UTC)