Wikipedia:Reference desk/Archives/Science/2011 January 18

= January 18 =

Rocking Cooking Pot
What causes a (metal) cooking pot (no handle) to rock from side-to-side when on a stove burner (electric in my case) just as the water is about to boil? This motion can be halted temporarily by grasping the pot briefly. When released, the rocking resumes.--Koosharem (talk) 01:20, 18 January 2011 (UTC)
 * Even before proper boiling, bubbles form in the water. These bubbles can exert forces on the walls of the pot.  It could also be from Cavitation, which is the net effect of lots of tiny shock waves created by tiny bubbles collapsing.  -- Jayron  32  03:03, 18 January 2011 (UTC)
 * Short, uncomplicated answer - The water is moving. Roger (talk) 07:43, 18 January 2011 (UTC)

undetectable viral load risk
how risky is it for those that have unprotected sex with someone that is hiv+ but has an undetectable viral load? I know that most people get HIV from other people that have just gotten it because those people have the highest amounts of replicas of the virus in their bloodstream. I know it is less likely that you would get hiv from someone on antiretrovirals or that is undetectable but is it nearly safe sex or not? Are there any statistics on this? Where would I find the answer to this question?Thisbites (talk) 01:29, 18 January 2011 (UTC)
 * See the second to last question here and this briefing sheet. Ariel. (talk) 01:45, 18 January 2011 (UTC)

Accessing Previous Questions and Dates asked.
How do I access a previously asked question.eg Jan 8 2011? —Preceding unsigned comment added by 118.208.117.68 (talk) 02:01, 18 January 2011 (UTC)
 * You can search the reference desk archives with the "search" button at the top of this page; or you can browse them at Reference desk/Archives. Here is Reference_desk/Archives/Science/2011 January 8.  Nimur (talk) 02:10, 18 January 2011 (UTC)

Light Sails.
Arthur C Clarke and others have postulated "Gossamer thin sails" for interstellar travel using light presure.Since light by definition is massless how can it exert pressure to 'fill' the sails? John Cowell118.208.117.68 (talk) 02:15, 18 January 2011 (UTC)


 * See solar sail, which operate by radiation pressure. -- Finlay McWalter ☻ Talk 02:21, 18 January 2011 (UTC)


 * Photons (light) have momentum even though they have no mass. In modern physics, relativistic momentum is more complicated than just the simple "mass × velocity" relationship; in fact, momentum is related to the mass, velocity, and energy of the particle, according to a Lorentz transform.  (So, even zero-mass photons can have non-zero momentum).  This was formalized by Einstein as part of the theory of Special Relativity.  Nimur (talk) 02:25, 18 January 2011 (UTC)
 * Photons have no rest mass. However, they clearly have energy and energy is mass, so anything which has energy can also exert a force.  The photoelectric effect, not-so-coincidentally also described by Einstein at the same time he explained special relativity is an atomic-scale example of a massless photon moving a massed particle (the electron).   It works just as well on solar sails.  -- Jayron  32  03:00, 18 January 2011 (UTC)


 * Photons are not massless. They have no rest mass (or to put it another way, at rest they don't exist), but while in transit they do have mass. Ariel. (talk) 03:01, 18 January 2011 (UTC)
 * There's no disagreement about the physics here - this is strictly a matter of semantics and terminology. I use the term "mass" to specifically refer to rest mass - as do many physicists.  An equally-valid but different definition of the unqualified term "mass" refers to the sum of the rest mass plus the normalized kinetic energy, per mass-energy equivalence.  Photons have an exactly-zero rest mass.  Many physicists (myself included) thus say "it has no mass."  Many other physicists dislike this terminology, and always use "mass" to refer to relativistic mass.  I don't think we need to devolve in to word-mungling pedantry over this, because we're all in agreement about the actual phenomena.  See the mass article, the terminology section, and the list of reference texts and papers for a bunch of different opinions about which definition is "better." Nimur (talk) 04:08, 18 January 2011 (UTC)
 * I wasn't arguing with you (not sure if you thought I was), it was a reply to the OP. I prefer to assign the word mass to relativistic mass because that's the one you need to use for calculations - momentum, gravity, inertia, etc. The trouble with doing so is that relativistic mass is not a constant (because it depends on who you are comparing it with), so I understand the arguments for assigning it to rest mass. Ariel. (talk) 04:22, 18 January 2011 (UTC)

Energy in a magnet.
For more than 20 years I used a 3 inch magnet on a daily basis.It was so strong it would fly out of my hand if I got too close steel and the only way to release it from the deck of my truck was to slide it to the edge and carefuly remove.As a tool of trade for a scrap metal buyer it even exerted a 'pull' on 304 and 316 stainless steel.It was used for holding steel for welding,holding spring doors open etc.It would have lifted the equivalent of hundreds of tons over the years without diminishing in strength. How can so much potential energy be incorporated in something so small,how is it stored and calculated,and surely there must be a multitude more practical uses for such a mini powerpack other than computers and maybe speakers? John Cowell118.208.117.68 (talk) 03:07, 18 January 2011 (UTC)
 * The nutshell answer is that a magnet exerts force, which is neither energy nor work. Work, rather, is force acting over a distance.  When the magnet leaps from your hand to the steel, it's done some work, because it's moved.  However, it's then stuck to the steel and does no further work.  For it to move again, you've got to do work of your own (counteracting the work the magnet did) to get it back away from the steel.  As for other practical uses (I'll leave aside whether they're more practical, as computers are way up there), magnets are essential to electric motors, generators, transformers, and medical devices.  &mdash; Lomn 05:14, 18 January 2011 (UTC)
 * I was thinking about this the other day again because magnet questions are quite common on the ref desk. Maybe someone has used this analogy before but I thought a spring analogy might be good at illustrating the difference between force and energy. A loaded spring exerts a strong force, try holding a strong spring closed just with your arms for a long time! It can take a lot of energy on YOUR part. But a spring can only do an amount of work relative to its length and force it was loaded with to begin with. Once a spring is "unloaded" that's it, no more force. Same as a magnet. Vespine (talk) 05:48, 18 January 2011 (UTC)


 * OP, This is by no means the first time a human has had this thought! :) Magnets are quite baffling until you understand how they work. It's the mystery of magnets that has led men on life-long fruitless and often fraudulent attempts at gaining "free" energy/money (Steorn, for example). Until a material is discovered that can block magnetic fields, no "work" can be done by them, just simple attraction. They are still fun to play with thoughZzubnik (talk) —Preceding undated comment added 12:39, 18 January 2011 (UTC).
 * This work has some interesting things to say regarding the science behind magnets. -- Jayron  32  14:43, 18 January 2011 (UTC)
 * For those of you wondering, the song in the link Jayron gave is the source of the "Fucking magnets, how do they work?" Internet meme (which may not really be a meme, the talk page argues...). Also, I never realized people got hung up about the use of the word "miracles" in that song :rolleyes: TomorrowTime (talk) 15:16, 18 January 2011 (UTC)
 * Ha ha ha, that is silly. This is how they work YouTube link to discussion of how magnets work..Zzubnik (talk) 17:01, 18 January 2011 (UTC)
 * I'd like to point out the enormous work I do every day by exerting a force of mumble Newton with by behind to the seat of my chair - not to mention the nightly work quota I exert on my bed. ;-) --Stephan Schulz (talk) 17:32, 18 January 2011 (UTC)
 * The Tesla is not actually a unit of energy, so you can't say how much energy it takes to make a magnet of a certain strength. And yet, it would be interesting to know how much actual energy it takes to turn a non-magnetic chunk of metal or rare earth into a powerful magnet like the one described; and conversely whether there is any theoretical way by which the entropy of the magnet as it degrades from perfect order could be used to drive a thermodynamic process that produces work.  Hmmm - is this the same as a measurement of any excess thermal energy released if the magnet is pulverized under a powerful ram?  I would think that the amount of energy needed to create two magnets of opposite polarity must exceed the amount of energy they release by coming forcefully together - I suspect that this is by some large factor - I wonder what physical factor describes this necessary limitation on the ease with which permanent magnetism can be induced in a material. Wnt (talk) 06:10, 19 January 2011 (UTC)
 * I suspect that the 'crushing' process would actually be endothermic, not exothermic. Ordered, aligned spins in a ferromagnetic material have a lower energy than randomly oriented spins; you have to put in energy to break the alignment.  At the Curie temperature, a phase transition occurs when you move from aligned to random spins; this shows up as a measurable endothermic bump by differential thermal analysis.  Similarly, if you just pull aligned-spin particles or domains apart without jumbling their orientations, that costs you energy as well &mdash; the energy of aligned spins is lower than the energy of the free or separated particles. TenOfAllTrades(talk) 14:30, 19 January 2011 (UTC)
 * Well, I have to admit, you're right about that. My intuitive feeling was that a pile of powdered magnet shouldn't spontaneously assemble into a powerful magnet ball - I wonder if that was also false. Wnt (talk) 18:07, 19 January 2011 (UTC)

Will an object past the event horizon of a black hole inevitably reach the singularity?
An object around a gravitational body like the Earth can orbit indefinitely if its velocity is sufficiently high, but is it possible for an object to remain stationary within a black hole? Likewise, can an observer past the event horizon perceive other objects? By definition, light can not escape the horizon, so would it be impossible for photons to reach the observer from further within the black hole? —Preceding unsigned comment added by 68.40.57.1 (talk) 03:27, 18 January 2011 (UTC)


 * Yes, in case of Schwarzschild black hole, object that crosses event horizon reaches the singularity sooner or later. All the paths inside of event horizon lead to singularity. So harder it tries to avoid, sooner it reaches singularity. For other types of black holes (charged or rotating black holes), there is possibility of avoiding singularity. I am doubtful whether an object can remain stationary within a black hole. About your last question, are you asking whether photons from within black hole can reach observer who is outside event horizon? No, photons cannot escape from black hole. Or, are you asking whether observer within the black hole can observe photons? Yes, observer falling inside black hole continues to observer things according to his clock, he cannot determine whether he has reached event horizon or has crossed it. - manya (talk) 04:21, 18 January 2011 (UTC)


 * To clarify, I was asking whether the observer within the event horizon can detect photons from further inside the black hole. Also, your statement regarding the observer not being able to determine whether he has reached the event horizon is in contradiction of the article on it. --68.40.57.1 (talk) 04:34, 18 January 2011 (UTC)


 * No, it is exactlyt confirmed by the event horizon article. Let me quote it for you.  "An observer crossing a black hole event horizon can calculate the moment they've crossed it, but will not actually see or feel anything special happen at that moment."  -- Jayron  32  04:40, 18 January 2011 (UTC)


 * I presume you meant to say "within the event horizon", not "within the singularity". Yes, for a while an observer inside the event horizon will be able to see an object that's further inside the black hole, that fell in shortly before the observer.  However, the object will rapidly move further away from the observer, due to the extreme tidal forces, and the object's image will become red shifted, to the point where the observer soon won't be able to see it at all.  In other words, the appearance of the object will qualitatively appear very similar to the appearance of an infalling object as seen from an observer that's outside the event horizon.  Red Act (talk) 06:16, 18 January 2011 (UTC)


 * KruskalKoords.gif have to be specific about what you mean by "further inside", because black hole spacetimes are nothing like the ordinary flat space where concepts like "inside" are normally defined and make sense. The most obvious thing you might mean by "further inside" is that the Schwarzschild r coordinate is smaller. Outside the event horizon, that coordinate measures distance from the center of the hole, more or less. Inside the event horizon, though, it measures time. The singularity is in the future, not in a particular place, and "further inside", in this sense, would really be "later in time". You can't see the future, even inside a black hole. You can, however, see objects that crossed the event horizon before you did. The easiest way to understand how this works is to look at a diagram like the one to the right. Ignore everything but the upper right quadrant. The straight diagonal line is the event horizon; below and to the right of that is the outside world; above and to the left is the black hole interior. The singularity is the boundary of the grey region. The grey region itself is nothing (it's not part of the solution). The past is down, the future is up. Light travels along 45° diagonal lines. You can only cross the event horizon from right to left, since you're limited by the speed of light. If you draw two sub-light worldlines crossing the horizon, it's easy to see that light from the first one will reach the second, so you can see someone who crossed the horizon before you did. You will hit the singularity before you see them hit the singularity, though. The animated blue lines are lines of constant Schwarzschild r. -- BenRG (talk) 07:25, 18 January 2011 (UTC)

Ticklish sensation near forehead
If an object is brought close to my forehead, but does not touch it, my forehead becomes sensitive and starts tingling and becoming very "ticklish", for lack of a better term. For several years, I've asked certain people if they've had the same sensation, and I've only met one girl who did. I have unsuccessfully tried testing the sensation with my eyes closed. As the object (any object) is brought closer to the forehead, the sensation deepens. It used to be really bad when I was a child, but now as an adult, I hardly even think about it anymore. It just popped into my head a minute ago and I decided to ask about it :)Reflectionsinglass (talk) 03:56, 18 January 2011 (UTC)


 * You are not alone. -- I'm particularly interested in this comment from DocCathode:
 * "Nothing supernatural about it. It's a mixture of a sense of danger/discomfort, the urge to move away, and the repression of that urge.
 * "To prove this, you need a friend who trusts you and follows instructions. Tell them to stay still, and to open and close their eyes when you tell them. Begin approaching with finger about two feet away. Tell them to close their eyes. Move the finger foot closer and tell them to open their eyes. Tell them to close their eyes. Move the finger to six inches away. Tell them to open their eyes. Tell them to close their eyes. Move the finger to three inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to two inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to an inch. Tell them to open their eyes. Tell them to close their eyes. Move the the finger to half an inch from their forhead. Tell them to open their eyes. Tell them to close their eyes. Slowly and quietly move your arm away from them. Tell them to open their eyes.
 * "The tingling sensation is most intense the last time, despite the fact the no object is near their forehead."
 * Please try that and let us know what happens. 71.198.176.22 (talk) 05:57, 18 January 2011 (UTC)

what killed Dinosaurs
I read an article that had say something about the death of mamots in 35000years ago that may be general for last happening for dinosoros 0 the radiation of any supper nova can kill dinosoros in some million years ago. A.mohammadzade jan 18 iran  —Preceding unsigned comment added by 78.38.28.3 (talk) 04:23, 18 January 2011 (UTC)
 * I'm not sure I understand your question properly. Dinosaurs became extinct during the Cretaceous–Tertiary extinction event. There are various theories about what caused this to happen. The most popular theories have to do with an asteroid (or asteroids) hitting the earth. You may also find the simple wikipedia article or the farsi wikipedia article on this topic to be helpful. Calliopejen1 (talk) 04:55, 18 January 2011 (UTC)
 * 3500 years ago? Are you thinking about Noah's flood (Nuh in Islam)? According to the (Christian) Ussher chronology this occurred 2348 BCE. Modern science places the dinosaurs extinction to the Cretaceous–Tertiary event 65.5 million years ago (as Calliopejen1 noted), and woolly mammoths to about 10 thousand years ago. BTW, several web-browsers have spell-checkers for their text-entry boxes; you should consider installing one for all the languages you speak. CS Miller (talk) 05:36, 18 January 2011 (UTC)
 * We have an article on near-Earth supernovae, which discusses their effects. A supernova is believed to have caused the Ordovician-Silurian extinction events, which was one of the first major extinctions, around 450 million years ago. CS Miller (talk) 05:45, 18 January 2011 (UTC)
 * Actually, the OP said 35,000 years ago, not 3,500 - no need to drag young earth creationism into this. As you note, mammoths were still alive and well at that point, so it's a curious date to bring up. Our article on 35,000 BC No, we don't really have an article on that date, but it is a nice redirect... doesn't mention anything particularly germane. 15:08, 18 January 2011 (UTC)
 * Ooops. My apologies. I can only think the lack of punctuation made me not see one of the zeros, and conflate the OP's timescale with that of YECs. CS Miller (talk) 17:05, 18 January 2011 (UTC)
 * There is really no question that the asteroid killed the dinos. Headline writers and popular science in general will never tire of stirring up controversies, but a panel of 41 international experts have met and agreed that there is consensus on the cause. This is mentioned in the articles. Imagine Reason (talk) 00:00, 19 January 2011 (UTC)
 * Actually, I killed the dinosaurs. It was a time travel mistake, sorry, but when you gotta sneeze, you gotta sneeze.  I take no responsibility for the mammoths, though.  I think Baseball Bugs did them in.  -- Ludwigs 2  00:04, 19 January 2011 (UTC)
 * I thought Tezuka killed the dinosaurs. — DanielLC 06:02, 19 January 2011 (UTC)
 * Really? Could've sworn it was Adric. Crimsonraptor &#124; (Contact me) Dumpster dive if you must 14:23, 19 January 2011 (UTC)

Sprouts with quickly growing roots
What is the fastest growing, soil erosion preventing, preferably edible plant suitable for San Francisco's climate? 71.198.176.22 (talk) 05:47, 18 January 2011 (UTC)


 * Lespedeza are commonly used in the Southeastern U.S. and meet all of your requirements except edibility. Not sure if it will grow in the Bay area, however.  -- Jayron  32  05:53, 18 January 2011 (UTC)

never say death star for pulsars
the crab nebula is sending several rays and is alive there in space. the heart of the star is sending palses so we ought never say the super nova has died. a. mohammad zade    iran --78.38.28.3 (talk) 06:06, 18 January 2011 (UTC)
 * There is no question that the crab nebula article uses the term "dead" only when citing . 71.198.176.22 (talk) 06:03, 18 January 2011 (UTC)

when the earth was shining
i think that the earth was shining for some million years. if you want to know why then that will explain with my new theory  a. mohammad zade
 * Why don't you ask whether your theory is consistent with the evidence so we can critique it for you? To do so, you would have to explain it. It is true that the elements heavier than iron came from supernovae in the Earth's distant past. 71.198.176.22 (talk) 06:06, 18 January 2011 (UTC)
 * thanks for giving commnets .i will soon write my theory hear i have some problems in safe evaluation andpublishing . so i save it such as patent . it will wrote  here as soon as i published .--78.38.28.3 (talk) 06:13, 18 January 2011 (UTC)
 * The Earth is still shining, see earthshine. Pfly (talk) 10:54, 18 January 2011 (UTC)


 * Wikipedia is not the right place for people to develop their new theories. See our WP:Original Research policy.  Comet Tuttle (talk) 18:38, 18 January 2011 (UTC)

Pre-existing conditions and Medical Insurance
I really don't understand why people who have a pre-existing conditions are making SUCH a big deal out of having to pay more for insurance. I understand they get mad if they are denied, but they should have to pay more. It's the same way I have to pay more for auto insurance because I am younger and have had several speeding tickets in the past few years, I am a greater risk. Many (not all, but many) CHOOSE to have these pre-existing conditions. Many people who are obese, choose to have several other related problems, many people who high cholesterol choose to have it, same with so many other conditions. Is there a flaw in my thinking? I'm already paying over $200 a month for insurance when I don't ever use it because of all these abusers, when I am perfectly healthy, take care of myself, follow a healthy diet, and go to the gym 5 days a week. If everyone was covered, it would just make the problem worse and more expensive for everyone. —Preceding unsigned comment added by 76.169.33.234 (talk) 07:44, 18 January 2011 (UTC)


 * What country are you from? People there might be grateful they don't live here in Australia.  Here, if you have a pre-existing condition, you can be denied any benefits for treatment of that condition for 12 months after taking out the insurance; but after that, you're fully covered like everybody else.  There's no alteration to premiums, though; that's strictly outlawed.  --   Jack of Oz   [your turn]  08:00, 18 January 2011 (UTC)


 * USA. I don't know how people think in Australia or in other countries, but I work in a pharmacy and my customers think just because they are taking a cholesterol medication, they can eat whatever they want. My customer was joking about it the other day. —Preceding unsigned comment added by 76.169.33.234 (talk) 08:04, 18 January 2011 (UTC)


 * Yes, insurance companies have to discriminate, but it's sometimes hard to be tough on those with self-inflicted conditions while being fair to those whose ailments are innocently gained. HiLo48 (talk) 08:09, 18 January 2011 (UTC)
 * No, insurance companies don't have to discriminate, but only if you run a system of compulsary insurance. This is what happens, in one form or another, across most of the developed world: compulsary insurance with a ban on discrimination. Physchim62 (talk) 12:39, 18 January 2011 (UTC)
 * I'm actually kind of struck by your first sentence. My fiancee, in trying to get private coverage, has been rejected by every insurer in California due to a pre-existing condition, which we're told will continue to be the case for another couple years. This is not a matter of paying more - she's not even allowed in the existing high-risk pools. I hate to think where she'd be if neither she nor I had a job. HIPAA and COBRA (expensive) do ignore pre-existing conditions, but they are not available to everyone. As for whether people choose to have a pre-existing condition, I have no comment. Someguy1221 (talk) 08:15, 18 January 2011 (UTC)


 * HIPAA is a health information privacy act, not an insurance company. COBRA is Federally mandated insurance coverage for those who recently left employment.  I do not see how those apply in the context you are using. --  k a i n a w &trade; 17:28, 18 January 2011 (UTC)


 * Further, California has a state managed program specifically for high-risk patients who have been denied insurance. It is explained here. --  k a i n a w &trade; 17:31, 18 January 2011 (UTC)


 * I wasn't even aware of that plan, thanks (but thankfully she has a job, and I don't even want to know how much that costs). I was referring to HIPAA health plans, by the way. I was using both that and COBRA as examples of coverage potentially available to individuals with pre-existing conditions who do not get such coverage through their current employer, or who are unemployed. Someguy1221 (talk) 00:04, 19 January 2011 (UTC)

Really it is a question of what costs we think are fair to spread across society, and which we don't. If you happen to be develop a terribly expensive health condition, through no fault of your own, should society bear this cost, or should you? Thinking from a position behind the veil of ignorance, one might prefer to spread such costs across society. Also, you note that some health conditions are in part caused by deliberate choices. This may be true, but most health conditions are not, and what sort of surveillance regime would be necessary to monitor which people this applies to? Such surveillance would likely be prohibitively expensive, as well as intrusive on privacy. Thinking forward into the future, as genetic health data becomes more readily available, it is plausible that insurance companies could very easily calculate your health risks to a much greater precision. (Assuming this were legal.) Is this something you would want? It is essentially just an extension of your principle of paying a premium that reflects your health risks. It would assign costs much more precisely to the individual, but it would change the nature of health insurance as we know it. Now, health insurance effectively insures against the risk that you will get Alzheimer's, for example. In the future, perhaps it would already be known that you will get Alzheimer's (even now, there are some genetic markers identified that are highly correlated with it). Then, since your premiums would already reflect your future disease, you would bear the cost for your Alzheimer's treatment, and your insurance would only be effective against risks such as being hit by a car and needing emergency surgery. Would this be preferable? To me, probably not. YMMV. Calliopejen1 (talk) 11:11, 18 January 2011 (UTC)

What does this have to do with science? thx1138 (talk) 13:01, 18 January 2011 (UTC)
 * For the areas of science related to the question, see: Actuarial science. Risk assessment and probability are aspects of this thread. Also see Social sciences. The thread relates to economics, sociology, and psychology. See Medicine. The question is related to Health care. See Disease. Edison (talk) 16:41, 18 January 2011 (UTC)
 * Generally this is misplaced, although the degree to which disease is a "choice" could be more scientific. After all, obesity and even high cholesterol are controlled by genetic and other propensities (I suspect that there should be a dramatic role for epigenetics here...)  I feel that nothing but prejudice controls what people like the OP pick out as a "choice" - after all, the commuter who suffers injuries in a traffic accident also made a choice, right?  The skier who leaves his testes with a buried pole on the slopes, likewise.  The HIV victim, few would disagree, but what about the victim of flu or rotavirus or meningitis or malaria, who could have avoided it all just by staying inside his front door?
 * It may be more for the humanities desk to answer what the point is of having insurance if suffering a diagnosis means being denied insurance. Why not just keep your money and pay as you go, with no private bureaucrats pretending to serve you by driving up costs?  The problem is, no one wants to be diagnosed with anything, and as they are servants only of corporations and government the doctors are trusted far less than Mafia bookies, so preventative care becomes a pretty myth. Wnt (talk) 15:30, 18 January 2011 (UTC)
 * "Why should society pay for the consequences of someone's bad choices?" begs the question of bad things happening to people who have in no way brought it on themselves. It is a reasonable question whether a society should spread the medical costs across all members, or have a "Every man for himself and the devil take the hindmost" lifeboat ethic. A person can be bopping along, healthy as a horse at 20 and at 30, and at 40, never took a sick day, eating right, not smoking, exercising regularly, then suddenly they have some crippling injury or ailment, like a debilitating and persistent and ineradicable infection, or a crippling injury,  or cancer, or heart disease, or insulin dependent diabetes, with little hope of getting individual health insurance from a for-profit insurer. Many Americans live in a fantasy world where they will always have a policy from work. If the hospitalization means you can't work, and you don't have or lose  your employer-provided insurance, you are just out of luck when you need surgery or hospitalization which might cost $100,000. Figure on losing the home and spending every dollar of retirement savings. "Move in with the folks" is not an option when they are dead and gone. Even if someone with severely impaired health found a private insurer, it would cost more per month than they could pay, especially if they are not healthy and can only work part time or a lesser pay level than their previous fine career allowed. "Paying more for insurance because of a preexisting condition" may mean paying an extra $12,000 a year more than the basic insurance, or even more than that, which the unwell person simply cannot afford. According to a report, "80 percent of people with diabetes were uninsured after they lost health insurance coverage due to loss of a job or job change, divorce, change in income or health status, or a move. " It is not presently affordable for them.  Over 50 million Americans have no health insurance, so that if they do go to see a doctor or have tests, they must pay "list price," typically several times what the cost is for those with insurance, since Blue Cross et al reduce the price to a fraction of what the doctor, hospital or lab says it should cost. For instance, Xrays that the insurer writes down to $100, and which cost me $15 out of pocket, would have cost the uninsured $350. An EKG that would have cost the uninsured $1100 got written down by the insurer to under $300 (and only cost me under $30). Edison (talk) 16:59, 18 January 2011 (UTC)
 * Fom a european persepective the "devil take the hindermost" American health care system, or lack of it, is scandalous. Add that to guns being used freely, with gun-murders being 100 times more common per capita. They are not good adverts for the US. 92.24.183.183 (talk) 14:42, 19 January 2011 (UTC)
 * While I agree with all that you said (in particular, many medical conditions are not or not fully the result of irresponsible choices), there is also another aspect: It might be cheaper to pay for the effect of someones bad choices. Sick people typically can contribute less to society - imagine Stephen Hawking without universal health care. Similarly, desperate people will do desperate deeds. Would you rather pay for someones cancer treatment via a social insurance system, or pay for more police to keep desperate husbands, wives, or parents from robbing banks to pay for treatment? --Stephan Schulz (talk) 17:24, 18 January 2011 (UTC)
 * This is a valid point, but it really doesn't go far enough. Society has prevented disaster by various back-door ways of paying for health care for the poor, such as hospitals providing care and then just not getting paid for it, then working the costs into care for other patients.  But hospitals have become more and more commercialized, with less profitable sites even shutting down, and if political efforts to correct the situation are rebuffed, then you're left with a situation where a segment of the population denied access to health care would begin to turn on it as an enemy.  The effect of even a single ambulance bomb would be devastating (and how do you apply security precautions?).  The effect of three or four simultaneous attacks against all remaining hospitals of a metropolitan area would essentially put major health care out of commission for a hundred miles in any direction - even if such a homegrown al Qaida didn't manage to get their hands on the radiation sources inside the hospital ... Wnt (talk) 05:12, 19 January 2011 (UTC)


 * I have a concise answer: The argument (that people with pre-existing conditions should just suck it up and pay a lot more for their medical insurance) makes complete sense from an actuarial point of view, but it collides with many people's belief that a society should take care of its sick, even though this makes insurance more costly for the more-healthy.  Comet Tuttle (talk) 18:37, 18 January 2011 (UTC)
 * Yes. Once we have decided we will not let people simply die on the street, then we must assess the cost of emergency treatment and conclude that an ounce (or penny) of prevention is worth a pound (dollar) of cure, therefore the next step is to try to fund preventative care. Because whether through taxes or insurance premiums, you still have to pay for the sick, so might as well pay less for better results. SamuelRiv (talk) 22:10, 18 January 2011 (UTC)
 * This isn't really a science issue and is OT on the RD anyway but that probably applies to most of this discussion. The above is one of the arguments for measures to tackle obesity, smoking and other problems as well as encouraging healthy eating, exercise etc in countries with some sort of socialised medical care. Of course depending on the measures this can lead to claims of nanny state, food police, sin tax and whatever else and measuring the efficacy of such measures is generally difficult at best. And I've seen it argued smokers at least actually cost the system less in the long run, particularly where there are other costs (e.g. in NZ where a government funded pension is something most citizens past a certain age are entitled) due to the shorter lifespan even with their added medical bills. (Of course you then get in to complicated issues like whether they contribute less.) Unrelated to this but related to the earlier point you also get the complex issue of how much should be spent on treating people with a given expected outcome. For example, is it worth spending $100k on treatment that may increase the chance of living past 5 years from 5% to 10%? (Very simplistic of course, the outcome of many treatments come in things like improved quality of life which are generally subjective.) Ironically this was seen to some extent in the US with the recent debates when the death camps nonsense came up. Nil Einne (talk) 22:46, 18 January 2011 (UTC)


 * Most of the others have hit the main points here, but I just want to point out that insurance that covers you when you are healthy, but not when you are sick, is not really insurance. That's just a series of subsidized physical exams. The entire point of insurance is that you pool the resources of many so that when others are in hard times, they have resources as well. It is a sign of how screwed up the American medical system has become that the basic notion of insurance has been completely forgotten by most Americans, who just understand it as "the way I pay for routine checkups and prescriptions." It's about spreading the risk, plain and simple. --Mr.98 (talk) 03:30, 19 January 2011 (UTC)
 * The deal with paying for routine checkups is that's how the insurance companies manage their own risk. The costs of dealing with tragic diseases goes up considerably the later they are treated; insurance companies actually save themselves money by making sure you go to the doctor regularly to for physicals, and to get even "nuisance" issues checked (like the non-specific and usually benign but occasionally deadly "Flu-like symptoms").  The ideal "deal" between insurance companies and their customers is something like "You agree to get checked by doctors more often, and we'll cover it when shit goes really bad".  Same deal with prescription coverage; people would forgo necessary medicine if it's too expensive, and on the bulk these people will end up costing the insurance companies much more if you end up in the hospital getting treated for something your medicine could have prevented.  This is not a defense of the American insurance industry at all; they've basically dropped the ball with regards to their fiduciary responsibility towards their clients.  But in theory, the system is supposed to work as I describe.  -- Jayron  32  05:26, 19 January 2011 (UTC)
 * Isn't it the insurance company's fiduciary duty to do the bare minimum to brand the sick person with a permanent record of poor health, and help their client (the employer) to get rid of the problem before it amounts to a major expense? Wnt (talk) 18:11, 19 January 2011 (UTC)
 * Thank god for the National Health Service. It has made me disinclined to emigrate to a sunnier cheaper or less crowded country as I would not have the piece of mind of knowing that I would get unlimited free health care if I needed it. See also Universal health care. 92.24.183.183 (talk) 13:17, 19 January 2011 (UTC)


 * I am the OP, sorry it took me so long to get back to this post....

Edison, you are really sucked into the idea that obesity and high cholesterol is almost all about genetics, when it has little to do with it. The issue here is that for a genetic defect (not sure if this would be the right word) to be present, it would require the proper environment. Almost every single obese person eats horribly and that is a choice. Same with many people with high cholesterol. You can be thin and have high cholesterol, but if you really take a look at it, almost every single person with high cholesterol is overweight, many of them even obese. If you look at both groups, neither one in almost every consumes a "healthy" or a low calorie diet (low cholesterol diet in the high cholesterol patient) and they almost never exercise if they do at all. Most these people "think" they know how to diet, but they have no clue, they think 3000 calories a day or more is a diet. They think exercising is walking around the block or taking the stairs instead of taking the elevator. Try going into the gym and pounding the weights for an hour and then doing 45 minutes of hardcore cardio 5 days a week and then lets see if you still have high cholesterol or are obese after a year doing that and consuming a low calorie diet. I can guarantee you over 90% of the people will be cured as long as they keep it up.


 * Now lets discuss choices in life. Everything you do is a "choice." Many or all of them involve some degree of risk. Everyone knows that driving a car involves risk, you can get into an accident. Some people choose to take that risk and some paranoid people or people that have been in very bad accidents that have not recovered emotionally choose to not take that risk. So is it a choice? Yes, it is. At my age, I choose to take the risk of maxing my car out to see how fast it goes on the freeway. I know there is more risk involved going very fast, but if I had children, I would not take that risk. Same with skiing, there is a risk involved. An example that may be more clear would be weight lifting, there is a great deal of risk involved. Personally, I choose not to do some exercises at the gym because of the risk involved. And yes, even with sex and contracting HIV there is a risk. Have you not heard of getting tested yourself and having your partner tested before you have unprotected sex? Do you think its a good idea to have sex with a woman or a male that has had 50 partners in the past? Would you take that risk? Some people would, some people wouldn't. That is called a choice. There is a distinction between acceptable risk and unacceptable risk.


 * The real issue here is that many diseases are preventable. Look at most people with type 2 diabetes. If they lose the damn weight and exercise, most of them would be cured. I work with one of them, he has either Jack in the Box, Kentucky fried chicken, or McDonalds every single day. Then he has 2 snickers and peanut M&Ms on top of it. He has high cholesterol and is overweight because of all that junk too. He never goes to the gym and has no interest at all in dieting. His blood sugar was dangerously high before he found out (at work by the way). As previously mentioned, going to the doctor for preventative care can reduce the chances of contracting several diseases or at least you can cut down costs to treat the disease if you catch it early. Most people don't even do that and it costs us healthy people tons of money. Some older women don't get mammograms as often as they should, others don't get them at all. Some older people don't get colonoscopies. Other people don't get their yearly physicals and dont people don't want to pay for their medication and think they know better than their doctor. In the end, it costs us money. It just hurts my wallet and others when I take good care of myself, eat healthy, exercise, and get regular checkups and do everything necessary to stay healthy and other people don't and I have to pay for it. There is no reason why I should have to. ALSO, let me add something to what I originally said. I don't have an issue with supporting people who are disabled and cannot work, I don't have a problem paying for their healthcare. I'm also kind of OK supporting some people who's income is around the poverty level, but then again, I do believe if they really wanted to, they could somehow, someway, come up with the money. I mean just imagine, the last time you really wanted something you could not really afford, didn't you figure out a way to come up with the money? I always do and so do many other people. —Preceding unsigned comment added by 76.169.33.234 (talk) 09:34, 20 January 2011 (UTC)


 * I'm gonna skip all the non-sense rant about having to burden the expenses of other people's choices (Welcome to life in society. Go be an hermit if you don't like it) and go directly to the only point of your post worth commenting on. YOU SHOULDN'T SPEED IN THE FREEWAY JUST FOR THE FUN OF IT. I sincerely hope that you get caught next time you do it, making the freeways safer for the rest of us. Dauto (talk) 16:27, 20 January 2011 (UTC)


 * To all the "Blame the victim" ranters: Heart disease, strokes, type 1 diabetes, (and even type 2 diabetes) and cancer, not to mention infections and injuries, happen all the time to those who take good care of their bodies. Some diseases are more prevalent among those who eat greasy food 10 times a day, smoke and never exercise, but you could still fill any number of hospital beds with those victims who are "blameless." Edison (talk) 22:35, 21 January 2011 (UTC)

Tidal Locking Formula
You have an article Tidal Locking

You have two formulas under the section "Timescale"

Two different science textbooks are quoted for the source of these formula: B. Gladman et al. (1996). "Synchronous Locking of Tidally Evolving Satellites". Icarus 122: 166. 10.1006/icar.1996.0117. (See pages 169-170 of this article. Formula (9) is quoted here, which comes from S.J. Peale, Rotation histories of the natural satellites, in J.A. Burns, ed (1977). Planetary Satellites. Tucson: University of Arizona Press. pp. 87–112.)

Do both formulas come from the same publication?PaulNethercott (talk) 09:25, 18 January 2011 (UTC)


 * I fixed the link for you, and placed a link on the doi from the reference. Hopefully someone has access to read the article and can check for you. Ariel. (talk) 10:49, 18 January 2011 (UTC)
 * The article is available online here (PDF). It gives the first formula and cites to Peale. I didn't look thoroughly for the second formula - maybe someone else can do that? (Note that the Wikipedia article does not cite the second formula to this journal article specifically, though perhaps it also comes from here.) Peale does not seem to be available online anywhere. (I searched in google books using a variety of ISBNs that seem to be associated with the book, and I didn't get any results.) If you are interested in verifying the formula in the original source, the Burns book seems to be available in many university libraries and large cities' public libraries, or you can buy it through Barnes & Noble for $1.99. Calliopejen1 (talk) 10:54, 18 January 2011 (UTC)

An object hanging on a string
On this page: http://www.croomphysics.com/notes/app_hewitt/chapter2.pdf (page 11) I found an answer to a question that confuses me: "Consider what would happen if you suspended a 10-N object midway along a very tight, horizontally stretched guitar string. Is it possible for the string to remain horizontal without a slight sag at the point of suspension?"

Answer: "No way! If the 10-N load is to hang in equilibrium, there must be a supporting 10-N upward resultant. The tension in each half of the guitar string must form a parallelogram with a vertically upward 10-N resultant."

I understand this for a guitar string and a 10-N load, but what if the string is replaced by a strong rope, and the load is only 1 N. Surely it must be possible to pull at both ends of the rope with enough force to make it remain horizontal without a sag??? Actually, I tried this myself with a piece of rope that I pulled apart and a pair of scissors, and there was no perceptible sag. My reasoning is that a stretched rope must be able to exert an upward directed normal force in the same way as a table exerts an upward directed normal force. Am I correct?? Lova Falk    talk   13:05, 18 January 2011 (UTC)
 * No. Your rope cannot exert a force at right-angles to itself. The only way it can hold something up is if it is pulling up at the point of the suspended object (to cancel the object's gravitational downward pull). If it's pulling up, it must have a vertical component to its direction, which means it's distorted down from perfectly horizontal. Once you recognize "one mass, one string", there's no basis for making a cutoff "only if the mass is less than a certain amount" or "only if the string has certain elasticity". For a very light mass on a very stiff string, the deflection is just very small (because the mass is light, doesn't require much upward pull, and that can be accomplished without much deflection because the string is so non-stretchy). DMacks (talk) 13:13, 18 January 2011 (UTC)
 * No, there should always be a sag, but the sag may not be perceptible under certain parameters. A non-ridged string should always sag in the middle if supported only at the ends, regardless of how hard you pull it. What your eye defines for you as "horizontal" may have a higher tolerance than a true horizontal. In fact, horizontal is one of the least stable positions for such an arrangement, if you look at something like bridges; all rope bridges sag in the middle; if you try to make them not sag, then you end up putting so much force on the ropes as to make them too close to the breaking point for safety. In Suspension bridges, you often engineer the roadway to sort-of "reverse sag", that is many such bridges actually have a hill in the middle, in effect redirecting the stress into the ground anchors on either side of the bridge.  -- Jayron  32  13:16, 18 January 2011 (UTC)
 * Thank you! :)  Lova Falk     talk   13:26, 18 January 2011 (UTC)
 * Indeed, the rope will sag under its own weight, even if you don't have any additional suspended mass. If the rope's mass is uniformly distributed along its length, it will form what is known as a catenary curve. TenOfAllTrades(talk) 15:12, 18 January 2011 (UTC)
 * Another perspective: in physics problems, 'rope' is often modeled as a mass-less object that has tensile strength but no compressive strength. Real ropes DO have compressive strength, especially large diameter ropes of short length. A short length of thick rope (~6" diam X 3' long), anchored at both ends can support an upright load-bearing catenary like the gateway arch. This would not usually be considered 'sagging'. SemanticMantis (talk) 17:37, 18 January 2011 (UTC)
 * I seem to recall an unintentional verse in a book by a distinguished scientist:
 * For no force, however great,
 * Can stretch a thread, however fine,
 * Into a horizontal line
 * That shall be absolutely straight.
 * --rossb (talk) 17:44, 19 January 2011 (UTC)
 * The exact wording of William Whewell's accidental poem was
 * Hence no force however great
 * Can stretch a cord however fine
 * Into an horizontal line
 * Which is absolutely straight.
 * as you can see here. Of course, he's talking about the weight of the cord itself, but the sentences just before that are about the case of a weight hanging from a cord whose own weight is negligible.  According to Martin Gardner in a Mathematical Games column reprinted in Martin Gardner's Sixth Book of Mathematical Games from Scientific American, Whewell was annoyed to learn about the "poem" and had the wording changed in the next edition.  Gardner misquotes the "poem" slightly, though. --Anonymous, 05:10 UTC, January 20/11.
 * Even the ground will sag if enough weight is put on it. Compressive strength means only that the material resists sagging, not that it avoids it entirely. Wnt (talk) 18:42, 19 January 2011 (UTC)


 * Sure, I just wanted to point out the limitations of the way string is often modeled for simple problems. In particular, a string modeled with no compressive strength cannot take the shape of an upright catenary, but a real rope can. This may help explain some of the confusion between real-world problems and physics 101 type stuff. SemanticMantis (talk) 20:59, 19 January 2011 (UTC)
 * What if both ends of the string are attached to spherical cows? -- Jayron  32  00:57, 20 January 2011 (UTC)

Planck length for Idiots
This basically translates into "the absolute smallest a thing can be and still physically exist", right? Half Shadow  18:23, 18 January 2011 (UTC)
 * Not really. It's a really, really small distance, so there are some theories that it's the fundamental granularity of the universe, but none of the well-accepted, well-proven physics theories hold that there is anything special about that length. It's just the length unit you get if you attempt to scale units such that major physical constants come out to unity ("natural units"). Keep in mind that the mass unit you get when you do that (the Planck mass, is 2.2 x 10-9 kg, about the size of a human egg cell (see Orders of magnitude (mass). -- 140.142.20.229 (talk) 18:46, 18 January 2011 (UTC)
 * As it says in Planck length: "In some theories or forms of quantum gravity, it is the length scale at which the structure of spacetime becomes dominated by quantum effects, giving it a discrete or foamy structure, but other theories of quantum gravity predict no such effects." Basically, we don't know what happens at such small scales. --Tango (talk) 21:56, 18 January 2011 (UTC)
 * I think you might fairly say that it's the absolute smallest a black hole that can exist. Any smaller, and the Compton wavelength gets bigger; but the Schwartzschild radius gets smaller.  Which means that the hole is too fuzzy to fit in the hole, so to speak.  So if you have a black hole that is evaporating by Hawking radiation, something ought to give out at least mathematically around this time; the Heisenberg principle says you're not supposed to know where the black hole is that precisely, but how is it going to get away?  You can play a merry chase through Planck mass, Planck length, Planck momentum, Matter wave to figure this out, but one word of caution - I initially looked up de Broglie wavelength to see how the math worked out and had a curious disagreement by a factor of 2 pi (on the Planck momentum; with the de Broglie wavelength you can't say a mass has a given wavelength without giving it some arbitrary velocity).  It turns out that there's a distinction between the "reduced" and "non-reduced" Compton wavelength as explained in that article.  A distinction which I don't understand... you'll need a real physicist for that... :( Wnt (talk) 05:02, 19 January 2011 (UTC)

Coal mining efficiency
I saw on a TV show this gigantic drilling machine many hundreds of feet below the surface around Pittsburgh, PA and started thinking about the massive amount of energy that must be needed to turn the thing's huge and undoubtedly heavy drill bits against the resistance of the earth it was drilling through, and the energy needed to move the thing forward, along with all the energy used for the other trolley cars, lights, ventilation systems, and of course the energy expenditures to raise the mined material back to the surface, and I wonder roughly how much energy quantified as an amount of coal (I know the machines don't take coal for fuel, but I want to know the figure in terms of coal) the average coal mining plant expends in all the actions it takes to extract 100 tons of coal? Just a very ballpark estimate is all I'm after here. For instance, do they use about a ton of coal's worth of energy to get 100 tons? Do they use over 50 tons' worth? Thanks. 20.137.18.50 (talk) 18:38, 18 January 2011 (UTC)
 * This is a very important and valuable analytic tool: it is formally known as EROEI (energy returned on energy invested). It is heavily studied by economists, business analysts, and geoscientists and engineers in the mining and production industries.  I know quite a bit about the ballpark numbers for the oil industry, but unfortunately not for coal; I imagine coal mining experts know similar metrics for coal mining.  I have heard reputable petrophysicists claim that the EROI for tar sands is dramatically and dangerously approaching 1.0 in the long run; this means that it is economically unsustainable (in other words, you must use one full barrel of oil to power the extraction of one barrel of oil).  Coal mining is different from petroleum, because the energy to extract coal comes from many sources: electricity (... from coal); chemical energy (from explosives... and you could trace the energy budget farther back to the factory, to electricity, and again, ...to coal); and petroleum (...imported from the oil industry). The oil industry, on the other hand, powers almost all of its field operational energy budget using energy derived from oil - so the budget is easier to balance.  (Machines, drills, motors, trucks, and so on, are all diesel or even fuel-oil powered).   As discussed in the article I just linked, the EROI is very difficult to measure exactly.  Nonetheless, the EROIE definitely does impact the business model of large-scale energy extraction.  Here is an OilDrum node on the EROI of coal.  Let me know if you need help deciphering the energy-budget numbers in there.  ("Lower-" and "Higher-" heating values, and so on, are all "engineering adjustments" that cloud the nice, pure theoretical thermodynamic analysis of "how many pounds of coal did we burn?")  And, as one post anecdotally claims, if you still live in an area where coal can be mined with a pick and shovel, (like Indonesia), you burn zero pounds of coal to extract 1 pound of coal - a net EROI of "infinity."  I would posit, based on comparative prices between coal and oil in BBOE, that coal extraction is significantly more energy-efficient than oil - let's say, 1 ton of coal burned to extract 10 tons of coal (in a developed, mechanized, American Wyoming strip mine).  In the spirit of providing solid, numerical references, there's no substitute for the cold, hard economic and production statistics collected by the United States Department of Energy, and made available at no charge to the public through the Energy Information Administration website.  Nimur (talk) 20:57, 18 January 2011 (UTC)

Stability
Did first-rate ships of the line such as the HMS Victory have any stability problems? It looks very top-heavy. Did it go a long way under the water? And does anyone have a picture of a model of it out of water? --  T H F S W  (T · C · E) 18:46, 18 January 2011 (UTC)
 * Some of your questions are obliquely answered in the article Ship of the line. In the earliest era of European warship building when trial-and-error and guesstimation ruled, stability was indeed a problem, as witnessed by the fates of HMS Mary Rose (1509) and Sweden's Vasa, but by Victory's era Naval architects worked by well-established scientific laws. Some of the more basic means of achieving stability are ballast below the waterline and the 'tumblehome' or inward angling of the upper decks, which significantly improved weight distribution. 87.81.230.195 (talk) 19:25, 18 January 2011 (UTC)
 * And does anyone have a picture of what the Victory would look like out of water? --  T H F S W  (T · C · E) 19:30, 18 January 2011 (UTC)
 * Well seeing as the Victory has been "out of the water"/in dry-dock for almost a century, I'd expect that most photographs that exist of the hull are "out of the water". Roger (talk) 20:12, 18 January 2011 (UTC)
 * My mistake, I thought it was in the water. Still, that doesn't answer my question: does anyone know where I could find a picture of the whole thing, or an accurate model? I mostly want to see the bottom. --  T H F S W  (T · C · E) 20:53, 18 January 2011 (UTC)
 * I think this site might be helpful. There are a number of reasonably good photos of what appears to be an accurate scale model, particularly this one.  Ka renjc 21:55, 18 January 2011 (UTC)
 * Out of water? Drink rum! Arrrrhhhh. Clarityfiend (talk) 07:37, 19 January 2011 (UTC)

A centreboard is a useful addition for stability. Trouble is, that article doesn't give much history. I'm personally aware of them being used on some sailing ships of the nineteenth century. HiLo48 (talk) 22:07, 18 January 2011 (UTC)
 * Personally aware? How old are you? DuncanHill (talk) 00:06, 19 January 2011 (UTC)
 * A centreboard or keel, as I learned earlier here, is mostly to keep the ship in a straight line. Anyways, thank you, the site Karenjc pointed out is exactly what I was looking for. --  T H F S W  (T · C · E) 00:37, 19 January 2011 (UTC)
 * Actually, a centerboard is mostly to keep a ship from drifting sideways with the wind. As a side effect, it does reduce rolling, but it adds little if anything to improve real stability, as it does not significantly change metacentric height. A keel can serve either or both purposes, drift reduction and increasing stability. --Stephan Schulz (talk) 19:35, 19 January 2011 (UTC)
 * Here's a picture of the Victory; there's no centreboard. The keel was also the main structural member of any wooden ship. Alansplodge (talk) 23:48, 20 January 2011 (UTC)