::On a second thought, if you are also allowed to use heat pumps (which are nothing more then heat engines running backwards), then it is possible to dump the work in the third body reversibly by pumping heat from one of the colder bodies into the hot one using the work extracted from the heat engine attached to the two fist bodies. If you are allowed to do that then the first method gives the correct answer. [[User:Dauto|Dauto]] ([[User talk:Dauto|talk]]) 14:33, 27 May 2010 (UTC)
::On a second thought, if you are also allowed to use heat pumps (which are nothing more then heat engines running backwards), then it is possible to dump the work in the third body reversibly by pumping heat from one of the colder bodies into the hot one using the work extracted from the heat engine attached to the two fist bodies. If you are allowed to do that then the first method gives the correct answer. [[User:Dauto|Dauto]] ([[User talk:Dauto|talk]]) 14:33, 27 May 2010 (UTC)
:::Thank you, that makes sense. Yes, you're allowed to use heat engines, heat pumps, refrigerators, and absolutely anything else in the world except outside energy. --[[Special:Contributions/99.237.234.104|99.237.234.104]] ([[User talk:99.237.234.104|talk]]) 03:27, 28 May 2010 (UTC)
== Shaker ==
== Shaker ==
Revision as of 03:27, 28 May 2010
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Technically aren't asphalt highways just oil spills mixed with dirt? 71.100.3.228 (talk) 02:26, 24 May 2010 (UTC)[reply]
No. Part of the definition of "spill" is that it is accidental. Also, asphalt is a specific component of crude oil, rather than crude oil itself. --Tango (talk) 02:32, 24 May 2010 (UTC)[reply]
That's right — fractional distillation is used to separate crude oil into things like gasoline, kerosene, and asphalt. But then the asphalt is indeed mixed with dirt; our asphalt article, in its Rolled asphalt concrete section, states that an asphalt highway is actually only 5% asphalt itself, and 95% "aggregates", meaning gravel, sand, and stones. Comet Tuttle (talk) 06:56, 24 May 2010 (UTC)[reply]
Roads and urbanization are a different form of habitat destruction than oil spills. They definitely all involve introduction of non-natural (or at least, non-local) materials into the environment, often significantly altering the local ecosystem. However, unlike oil spills, roads have a measurable benefit - improving the quality of life for humans - so there is at least some level of tradeoff to consider. Nimur (talk) 14:43, 24 May 2010 (UTC)[reply]
Asphalt is not a liquid, so it doesn't have the same effects that the liquid crude oil has on birds, fish, etc. --Chemicalinterest (talk) 14:55, 24 May 2010 (UTC)[reply]
Roads are also confined to discrete areas; their destruction is intense, but it covers only a fraction of land area. Roads generally do not move on their own, so animals have some hope of avoiding their hazard. Oil spills on water can spread widely and uncontrollably. Sea birds and other animals have trouble avoiding oil slicks. However, note that motor vehicles can drip appreciable amounts of engine oil onto road surfaces, which tends to run off during rain storms, thereby polluting the runoff. A busy roadway thus functions like a low-level oil spill that continues indefinitely. A widespread shift to battery electric vehicles and bicycles instead of the current dominance of internal combustion engine vehicles would greatly reduce oil pollution on road surfaces. --Teratornis (talk) 19:40, 24 May 2010 (UTC)[reply]
Well, if you're advocating some kind of worldwide mandate to ban automobiles and force everyone to use bicycles or glorified golf carts, then we will veto it in the United Nations before you can say "oil spill". This kind of change is absolutely out of the question for civilized, industrialized nations -- what about the eighteen-wheeler trucks that take merchandise from the warehouse to the local neighborhood store? A much better way would be to implement more frequent, more stringent and consistent mechanical inspection requirements for motor vehicles to make sure they don't drip motor oil all over the place -- this would achieve substantially the same result, but without nationwide economic upheaval that your proposal would cause. 67.170.215.166 (talk) 06:38, 25 May 2010 (UTC)[reply]
There are electric cars available today that are not remotely similar to golf carts — they have highway performance that matches up quite nicely with gasoline-powered cars. Range is a bit of a problem — the Chevy Volt has a nice interim solution, with a gasoline engine that doesn't kick in until it's needed, which except on long trips, it usually won't be.
The big problem with them, at the moment, is price. Hopefully that will come down.
But of course if/when that happens, if they're going to be our transportation solution for large numbers of people, then we're going to need a lot more generating capacity. I suspect the only realistic way of getting that much capacity, without producing lots of greenhouse gases, is to build a lot of nuclear plants. Unfortunately it takes upwards of a decade to get a nuclear plant on-line. That's why I think we need to get some in the pipeline starting now. --Trovatore (talk) 22:01, 25 May 2010 (UTC)[reply]
Excellent idea, why don't we write Congress and demand more nuclear reactors? 67.170.215.166 (talk) 01:41, 26 May 2010 (UTC)[reply]
acetone
does acetone evaporate like alcohol or does it leave a residue? can u use it on food surfaces? —Preceding unsigned comment added by Tom12350 (talk • contribs) 03:37, 24 May 2010 (UTC)[reply]
Yes, it evaporates very quickly, maybe not as quickly as most alcohols though. No, I would never use it on anything that would ever contact food. Beach drifter (talk) 03:44, 24 May 2010 (UTC)[reply]
After a little reading, it appears to be hardly toxic at all. I still see no reason you would need to use it in the kitchen. Beach drifter (talk) 03:47, 24 May 2010 (UTC)[reply]
can i use it on a plastic counter top, and a particle board kitchen table with a wood looking plastic/ vinyl vanear —Preceding unsigned comment added by Tom12350 (talk • contribs) 04:11, 24 May 2010 (UTC)[reply]
It's a solvent, so plastic-based and printed food surfaces might get damaged, or colors from packaging transfer. What would you intend to use it for? FT2(Talk | email) 04:12, 24 May 2010 (UTC)[reply]
There are lots of products specifically designed for this use, visit your local supermarket. Vespine (talk) 04:50, 24 May 2010 (UTC)[reply]
No. Don't use it on those - it will dissolve them, then evaporate, leaving an impossible to clean mess. Not really a mess - more like a mushy smear of the veneer. It's pretty non-toxic though (it's actually legal as a food additive!), and does not leave any residue behind, so in that regard it's safe in the kitchen. I use acetone to remove stickers. But you have to work VERY fast, it evaporates very quickly - even the open bottle will evaporate. Put the acetone on a tissue, and rub the sticker - don't put the acetone on the sticker, it will dissolve the glue, then run, leaving a bigger sticky spot than when you started. Ideally have a second person to cap the bottle in between putting some on the tissue. Acetone is probably the fastest evaporating solvent commonly available. Ariel. (talk) 05:32, 24 May 2010 (UTC)[reply]
A little WD-40 will remove stickers as well and there's no bottle to close. Dismas|(talk) 08:10, 24 May 2010 (UTC)[reply]
You dont' want to use that stuff in the kitchen, though, it leaves a mess and it can be toxic if ingested. 67.170.215.166 (talk) 06:43, 25 May 2010 (UTC)[reply]
How much are you using?! Do you lick your counter clean?! I doubt any reasonable person would A) use so much WD-40 as to be a health hazard and B) just let WD-40 sit on their counter after cleaning off sticker residue and then use that spot to make a sandwich. Dismas|(talk) 08:06, 25 May 2010 (UTC)[reply]
I'd rather not use any petroleum distillates in my kitchen, unless absolutely necessary. 67.170.215.166 (talk) 01:57, 26 May 2010 (UTC)[reply]
how will plastic-based and printed food surfaces get damage if they use it in labs to clean plastic labware? will it help if i dilute it 50-50 w/water? —Preceding unsigned comment added by Tom12350 (talk • contribs) 06:13, 24 May 2010 (UTC)[reply]
Not every plastic is the same, some will be totally unaffected, others will dissolve into goo - there are a LOT of different kinds of plastic. I don't know what water will do, probably it will slow down the dissolving. Ariel. (talk) 08:08, 24 May 2010 (UTC)[reply]
arent there only 7 kinds of plastic? —Preceding unsigned comment added by Tom12350 (talk • contribs) 08:41, 24 May 2010 (UTC)[reply]
There are many more! I used acetone in the lab and I saw somebody cleaning a keyboard. The Grey keys like Strg And Alt got very soft and the printed letters vanished, the other white keys showed no problem and ended up very clean.--Stone (talk) 09:37, 24 May 2010 (UTC)[reply]
The better cleaning agent for you might be, what other people use for disinfection, it is a mixture of 70% isopropanol and water.--Stone (talk) 09:37, 24 May 2010 (UTC)[reply]
i already tried that. will it help if i dilute acetone 50-50 w/water? —Preceding unsigned comment added by Tom12350 (talk • contribs) 10:49, 24 May 2010 (UTC)[reply]
That would slow its evaporation, but it would also slow its cleaning abilities, so there would be no net difference. You can put it in a spray bottle, not a mist one, a squirt one. --Chemicalinterest (talk) 11:02, 24 May 2010 (UTC)[reply]
i dont understand. if i dilute it wont it be less corrosive? —Preceding unsigned comment added by Tom12350 (talk • contribs) 11:14, 24 May 2010 (UTC)[reply]
Yes diluting it will make it less likely to damage the plastic. Alchohol is a better choice though if you have it. What are you cleaning?87.102.85.123 (talk) 11:47, 24 May 2010 (UTC)[reply]
I used to be a follower of the "throwing assorted chemical compounds on a surface makes it cleaner" school of thought, I must admit, but a lot of 'em will ruin your crap if you aren't careful. The way I see it, just because something kills bacteria and viruses doesn't mean it's safe for you to eat. It's not that antiseptics and antibac soap are actually making the surface cleaner on a microscopic scale - they're simply poisons designed to kill microbes instead of humans. Which is why you're supposed to wipe away the disinfectant before you eat off something you use it on. In the same vein, just because something is caustic doesn't mean it's necessarily going to clean whatever you put it on. And if its effects are 75% "creating a goopy catastrophe" and 25% "cleaning the surface", no matter how much you dilute it you're still going to get three times as much goop as cleaning action. ZigSaw 11:46, 24 May 2010 (UTC)[reply]
I don't understand why you are so intent on using acetone in your kitchen. Did you get a hold of an industrial quantity and just trying to use it on EVERYTHING? Lol… if you absolutely insist on using it, at least try rub some on the least conspicuous spot first and leave it for a few minutes and rub it again, see if it damages the surface before making a mess of it.. My know it all uncle once used to clean his fancy hi fi with metho, one day he decided that acetone might be a better idea and it melted the face of the LCD display making a matted mess you couldn't even see through, he was gutted. Vespine (talk) 23:13, 24 May 2010 (UTC)[reply]
Crystal Violet
Hi there :) My name is Elin and I'm from Sweden. Right now I'm writing an assay about terraforming in astrobiology with chemistry and biology as "main subjects". I'm now stuck on gram staining and I really need to know how crystal violet is produced. When I read this article: http://en.wikipedia.org/wiki/Crystal_violet, I don't quite get the production. Mostly it's because I don't understand everything that is written, for example I don't get if it's ment that it is redox (gain) or oxidation (loss) that happens when you oxidize the compund in the second prodction step. And what about the last step? Is that the final step to get crystal violet, or is it a step to produce something else since it says "Hydrolysis of crystal violet gives the carbinol"? And what is a leuco?
I've written about the first two steps, but I've left out what I've asked about (the oxidize-question, leuco and the third step). I feel like I should bring more to the table in order to get a higher grade and it would be sad if difficulties with language should stop me from getting the grade that I need.
Please try and explain clearly and detailed. I don't mean that I want it to be simple, just that i'm thankful if you explain a lot since I don't understand all english words.
Thanks a lot! /Elin —Preceding unsigned comment added by Ailithey (talk • contribs) 08:56, 24 May 2010 (UTC)[reply]
The leuco (white or colourless) form is oxidized with oxygen. The carbinol is a alcohol derived from methanol by substituting the hydrogen by something different, here the central C-OH is attached to three 4-dimethylaminopheny substituents.--Stone (talk) 09:46, 24 May 2010 (UTC)[reply]
Thanks a lot, I'm starting to get it. But if you look at the article http://en.wikipedia.org/wiki/Crystal_violet, I still don't really get the production. The ast step says this:
A typical oxidizing agent is manganese dioxide. Hydrolysis of crystal violet gives the carbinol:
[C(C6H4N(CH3)2)3]Cl + H2O → HOC(C6H4N(CH3)2)3 + HCl
Is this step part of the production of crystal violet? Do you get crystal violet by following all three steps, or is the last step the formula for the production of a carbinol? —Preceding unsigned comment added by Ailithey (talk • contribs) 10:38, 24 May 2010 (UTC)[reply]
It should be clear now. The last step was not part of production. 87.102.85.123 (talk) 12:06, 24 May 2010 (UTC)[reply]
center of mass
why does objects rotate around it's centre of mass ..?
I mean as a example, when we throw a rod (something like that) in the air holding at the edge,we can see it rotates around its CM.dany (talk) 13:19, 24 May 2010 (UTC)[reply]
Try to imagine an object that does not rotate around its CoM. Then that would mean that the CoM of the object would rotate around some point (inside or outside of the body). Therefore the CoM would be accelerating toward the point of rotation (centripetal acceleration). That would require an external force. Count Iblis (talk) 14:06, 24 May 2010 (UTC)[reply]
When an object is forced to rotate around something other than its center of mass by an external force, the object will precess, and if it continues to rotate for a long enough time (e.g., low friction or low damping), it will eventually change its rotation through a precession so that the rotation aligns with its principle axes. Nimur (talk) 14:48, 24 May 2010 (UTC)[reply]
Let's envision your example of the thrown rod. The center of mass will follow a parabolic path back to Earth, and in that respect the rod will act as if all its mass is located at the center of mass. In addition, the rod can have rotation around one or several axes, but the center of mass will still follow the same parabola. If it didn't, it would act like a thrown marble rippling up and down instead of following a parabola back toward earth. That would require energy instead of just gravity.Overjive (talk) 03:16, 26 May 2010 (UTC) —Preceding unsigned comment added by Overjive (talk • contribs)
aching muscles = laughing reflex?
Yesterday I played in an action cricket tournament. Being the most unfit person ever, today my muscles are all exacting their revenge on me and I could hardly roll myself out of bed this morning. Funny thing is, I discovered that whenever I move (and stretch some of my sore muscles) I get this urge to laugh for no apparent reason. Even thinking about it now makes me giggle. Is this a known thing or am I the only one? Could it be related to tickling (I'm VERY ticklish and laugh uncontrollably when people try to tickle me, even before they've made any contact)? I tried Googling but I'm getting false hits about laughing so much your muscles ache. Zunaid 16:28, 24 May 2010 (UTC)[reply]
You evidently have an easily-triggered laugh reflex, so perhaps the pain in your muscles triggers this by reminding you of the fact that you find the situation amusing. Dbfirs 06:57, 25 May 2010 (UTC)[reply]
I mixed solutions of sodium hypochlorite and sodium acetate together. Is the hypochlorite strong enough to oxidize the acetate ion? I noticed some gas being produced (not much), but otherwise there was no indication of a reaction. Thanks. --Chemicalinterest (talk) 17:19, 24 May 2010 (UTC)[reply]
(edit conflict with below) Oxidize it to what? Peracetic acid? Usually that's done with hydrogen peroxide, but hypochlorite isn't that much weaker of an oxidizing agent than peroxide, so I suppose it could. Even with hydrogen peroxide, the equilibrium still lies to the left, so it makes sense that only a little, if any acetic acid would be oxidized. Buddy431 (talk) 20:40, 24 May 2010 (UTC)[reply]
Did you look on a standard reduction potential table? We've linked them before, and there are many of them out there on the internet and in books as well; the numbers should tell you if it is possible for hypochlorite to oxidize acetate. The only possible products are the chloride ion and carbon dioxide, so if hypochlorite DID oxidize acetate, you'd get some bubbles. --Jayron32 20:31, 24 May 2010 (UTC)[reply]
The standard reduction table here doesn't have acetic acid, so no beans. And why do you say only that Chloride and CO2 are the only products? It could only be reduced to chloride gas (a weaker oxidizing agent than the hypochlorite), which could be the bubbles observed. Buddy431 (talk) 20:42, 24 May 2010 (UTC)[reply]
Doubtful. Chlorine gas disproportionates to hypochlorite and chloride in any basic solution, see Chlorine_bleach#Chemical_interactions. Cl2 may be an isolatable intermediate, but I think that spontaneously, the chloride ion ends up being the lowest-energy product here. Consider that the Eo for the reduction of chlorine gas is highly positive itself... --Jayron32 21:03, 24 May 2010 (UTC)[reply]
It's not clear what the reaction would be here:
Acetate oxidise to CO2 - can't find potentials either - note - acetic acid is quite resistant to oxidation - it's used as a solvent in many oxidation reaction.
Peroxide - maybe?
Reaction to form a chloroacetate - this seems quite likely - chlorite would be reduced in this reaction - so I suppose acetate must be oxidised. I'm fairly certain this reaction will go, don't know how fast.
There are simple tests to see if a reaction has happened - such as add chlorite to excess acetate, let it react, then add iodide - if chlorite remains iodine will be produced (visible), as a control compare with the control reaction (chlorite + water . no acetate) 77.86.125.207 (talk) 18:33, 25 May 2010 (UTC)[reply]
Special Relativity
One of the implications of Einstein's Theory of relativity is-
If two observers are in relative motion, they will not, in general, agree as to whether two events are simultaneous. If one observer finds them to be, the other, in general, will not.
Now I read this example in Halliday/Resnick, Fundamentals of Physics.
Two observers Sally and Sam stand in two long spaceships. They are stationed a the midpoint of the two ships. The relative velocity of ssSally with respect to ssSam is v separating along a common x axis. They are stuck by two meteorites just when they were crossing each other, one setting off a red flare and the other blue, leaving marks at R and B on ssSam and R' and B' on ssSally. Let us suppose that Sam and Sally are positioned right in the middle of R and B and R' and B'. Sam receives the two light waves at the same time and gave the following explanation.
Sam: Light from event red and light from event blue reached me at the same time. From the marks on my spaceship, I find that i was standing halfway between the two sources. Therefore, event red and event blue were simultaneous events.
Sally and the expanding wavefront from event red are moving towards each other, while she and the expanding wavefront from event blue are moving in the same direction. Thus, light from event red reaches her before light from event blue. Her explanation goes as follows.
Sally: Light from event red reached me before light from event blue did. From the marks on my spaceship, I find that i too was standing halfway between the two sources. Therefore, the events were not simultaneous.
These reports do not agree. Nevertheless, both observers are correct.
My question goes as follows:
If we observe the two spaceships from a third inertial reference frame, we will discover that the two events occurred simultaneously as they occurred at a unique instant when the two spaceships coincided on the x-axis. Does that mean Sally's explanation was wrong? If that is so, is the first postulate of the Theory of Special Relativity contradicted? Please explain the validity of Sally's explanation in this light.
--Lightfreak (talk) 18:20, 24 May 2010 (UTC)[reply]
You said that Sam is equidistant from R and B and saw light from the two flares at the same time. That means that the two collisions were simultaneous in the rest frame of Sam, so your third inertial frame is the same as the rest frame of Sam. There is no unique instant when the spaceships cross because they have length; it takes a while for them to pass each other completely. There is a unique instant in a unique inertial frame when the ships occupy the same range of x coordinates, but the collisions didn't happen at that instant. (One of them may have, but not both.)
I don't think there's much insight to be gained into special relativity by looking at different reference frames. It's like checking that 5+5+5 = 3+3+3+3+3 and 7+7+7+7 = 4+4+4+4+4+4+4 and so on. What you really want to understand is why multiplication is commutative in the first place; then you don't have to try all the special cases. The best way to understand this problem is to draw a spacetime diagram showing all of the events. -- BenRG (talk) 18:51, 24 May 2010 (UTC)[reply]
What is the point of a lawn?
Besides the aesthetic aspect, is there any coherent reason to constantly trim, weed, fertilise and reseed the part of your property with nothing built on it? I can understand preventing erosion, but wouldn't regular old wild weeds do that? Does anything horrible happen when grass gets too long? It seems to me that a ludicrous amount of money goes into herbicides, mowers/gas, fertilizers and all kinds of ugly side effects of fighting natural selection to get a "good-looking lawn". Unless there's some benefit I'm not seeing... ZigSaw 20:36, 24 May 2010 (UTC)[reply]
Small animals, some of which may be pests, can hide in tall grass. Jc3s5h (talk) 20:41, 24 May 2010 (UTC)[reply]
I figured lawns were a sign of the wealthy being able to afford land and to manicure it as well. As well as for aesthetic purposes, lawns provided ample grounds for one's "constitution" I suppose. More recently, lawns are smaller and part of the package when you buy a nice house. It's probably more for aesthetic purposes now than it ever was, because most lawns (at least around where I live) are so small, you can't even play Badminton on them. Backyards usually allow for a single sport and maybe that's it... barbecues and other activities are restrained to a porch. I know that with my family's country estate, we have no "lawn", because it's all overgrown and wild and absolutely beautiful. (According to lawn, it's still a lawn.) Of course, lawns at, like, Versailles, are simply ostentatious but stunning. – Kerαunoςcopia◁galaxies 20:43, 24 May 2010 (UTC)[reply]
There's nothing wrong with doing things for aesthetic purposes. You either do something because you want to adhere to cultural norms, or you do it specifically to fuck with cultural norms. So, either you maintain a lawn because its expected, and your culture tells you it looks good, or you let it grow wild because you want to intentionally go against those norms. Either position is equally valid, and both have as much weight. It comes down to personal aesthetic choice and little else. --Jayron32 20:52, 24 May 2010 (UTC)[reply]
Kids and pets can play on them. They are pleasant places to sit or snooze with a beer and a good book. Grass is basically outdoor carpeting. If you don't have grass then you have...what?
Nothing - you live in an apartment with no outdoor space.
Dirt - which you can't lie on and isn't comfortable to walk on - and is unusable for days after rain.
Xeriscape - less work but also uncomfortable to lie on. Also, doesn't naturally absorb dog poop and is hopeless for little kids to kick a ball around on.
Concrete - ugly, also not very useful for all the reasons above.
If you want extra space beyond your indoor living space, a garden...and therefore a "carpeted" garden is the way to go. Grass is the natural choice because unlike most other plants it's evolved to survive being grazed by herbivores - and can therefore be mowed to keep its height in check and to maintain the density needed.
Having said all that - my house is situated out in woodland and my kid is old enough not to need to go out and play in it - so we mostly have wild grass which doesn't grow too long because of the dense trees - and doesn't get mowed because we don't live someplace where we have to conform to social norms with manicured grass.
This probably goes back to the rise of surburban life - in the 20th century - before then people didn't have lawns - they either lived in towns (with almost certainly no garden at all) or in the countryside.. Lawns did exist prior to surburbanisation - notably common land such as the village green; the lawns would be 'mowed' mostly by sheep - which do a very good job.
The rise of surburban life meant that everyone got their own miniature village green - called a garden. (along with a miniature mock tudor mansion - or 'semi').
That is basically the origin of the grass lawn. Basically people now imitate the cutting sheep once did using lawnmowers. Strange behaviour but true. If you don't believe me ask on the humanities desk. Obviously grass is good for playing on. Doh, I just found out all this is at lawn, nobody will read it anyway. 87.102.85.123 (talk) 21:39, 24 May 2010 (UTC)[reply]
We do have a History of the lawn article: they appear to date from before the 20th century: the first lawnmower (as opposed to a scythe) was invented in 1827. Buddy431 (talk) 22:28, 24 May 2010 (UTC)[reply]
As mentioned above by many, having a lawn at the backyard is actually quite nice. I just want to point out that you don't really need to use herbicides, fertilisers or gas to have a nice lawn. I don't use any of that and still am quite happy with my lawn. Dauto (talk) 03:19, 25 May 2010 (UTC)[reply]
Some lawns have just the right amount of moisture from ground water and sun to only require mowing. Other lawns require watering and mowing. Other lawns require so many things that its better to zero-scape. If you use mulch to zero-scape then it will retain moisture and and allow the zero-scape plantings to thrive. The problem is when neighbors want to dictate whether you have grass or zeroscaping and constantly yap to the police. You should have the right to have any kind of "lawn" your heart desires that is affordable and not a hazard to others. Some people though claim that zeroscaping hampers firefighters and attracts venomous or disease carrying creatures. If the economy gets any worse though even fancy dancy bank lawns might be used to grow tomatoes. 71.100.8.229 (talk) 20:52, 25 May 2010 (UTC)[reply]
It's because lush, green grassland would have been a sign of plenty to our very distant ancestors. Food, water, and good visibility to protect against preditors. Even our eyes are structured to process horizontal objects more readily than vertical. It's a comfort factor that is bolstered by other social and cultural points raised above. 24.130.145.253 (talk) 04:33, 26 May 2010 (UTC)[reply]
Old Testament states "Adam has lived 930 years".How this can be explained? Real today's years, or possible short years of the old time? Does the length of years,as days,may be variable? Today 1 year=365 days, but billion years ago 1 year=15 days for example?TASDELEN (talk) 21:13, 24 May 2010 (UTC)[reply]
There's no evidence such intervals have changed that much in Earth's history. 67.243.7.245 (talk) 21:32, 24 May 2010 (UTC)[reply]
In scientific terms, it is explained by pointing out that many cultures have myths that are not scientifically accurate. Anything other than that is sheer interpretation. Creationists and others who are decidedly not scientific (in that they take their conclusions as givens and then work backwards from there) usually say things like "God let him live that long" and "since the time of the Flood people have been more and more sickly and sinful and degraded" and things of that nature. See e.g. Answers in Genesis, a young-earth creationist ministry. But there is absolutely zero scientific evidence for this and it is entirely implausible from a truly scientific standpoint. AIG happily distorts scientific evidence to fit its very literal interpretation of the Bible. Frankly I think (as a nonreligious person) that such analytical attempts miss out on the entire point of the Bible, which was not meant to be considered a science textbook. But that's a personal opinion, to be sure. --Mr.98 (talk) 21:34, 24 May 2010 (UTC)[reply]
(edit conflict with above x2) Look at this article we have: Longevity myths#Biblical. Some scholars argue that people inflate the lifespans of their important patriarchs and elders (sociological/anthropological reasons I guess, I'm not in this field, so I can't discuss that aspect any more). Note that most (i.e. all) non-religious scholars do not believe that there was a literal single first human (named Adam or otherwise). Buddy431 (talk) 21:37, 24 May 2010 (UTC)[reply]
(ECx3) I don't know why this is on the science desk since the obvious scientific answer is it's all nonsense, but AFAIK it's generally held by those who believe in those parts of the bible literally that human age was significantly reduced after the great flood. E.g. [1][2][3][4][5][6]. The reason for this is obviously something those who do believe in such things can't agree on, since it isn't really discussed in the bible but it's either thought of as a result of direct action by god (punishment or whatever), the problems/consequences that resulted from flood or the way humans have lived since then (see the earlier links some of which include discussion). Not to do with changes in the length of years AFAIK. Nil Einne (talk) 21:38, 24 May 2010 (UTC)[reply]
Not sure where you got a billion years from, neither creationists nor evolutionists would try to argue that anything like first humans were around a billion years ago. For some actual science, a DAY is determined by how fast the Earth spins on its own axis, a YEAR is determined by how long the Earth takes to orbit the sun. Days and years are independent of each other, a planet can have a long day and a short year, or a long year and a short day, there is no correlation. For example, in the Moon's orbit around the Earth, Moon days and years are actually equal, they are both one Earth month. We're less interested in length of days for the time being. As for years, the orbital period of any object around a much more massive object, like the Earth around the Sun is directly determined by the distance between the objects. This means: how far the Earth is from the Sun. The further apart the objects are the longer the orbital year. Mercury is only 0.4 of the distance from the Sun to the Earth and it has a year of about 88 days, Venus is 0.7 of the distance from the sun to the earth, it has a year of 224 days. Earth obviously takes 365 days to orbit the sun, Mars is 1.5 the distance from the Sun to the Earth and it has a year of 780 days. So for the earth to have a shorter year it would have to be closer to the Sun. There's no evidence that the Earth shuffled around or changed places since the formation of the solar system, there may have been some catastrophic events which changed the year a bit, but there's some decent evidence that the Earth has been at least in the Habitable zone, since life arose anyway. Vespine (talk) 22:42, 24 May 2010 (UTC)[reply]
So just for completeness, for Earth's year to be 15 days, it would have to be 0.15AU away from the Sun, that's a third of the distance to Mercury which is already a hot Sun scorched rock with any hope of an atmosphere blasted away long ago, quite certainly incapable of harbouring any life. So we can be pretty certain that at no stage during evolution of life was the Earth's year as short as 15 days. Going by the habitable zone link I gave above, I think shortest possible year that the Earth with life could have is about 345 days. Vespine (talk) 23:01, 24 May 2010 (UTC)[reply]
The explanation that I am familiar with is the confusion between the lunar month and the solar year that has occurred before the stories of the Bereyschitt (Book of Genesis) were written down. I think this is the explanation Zenon Kosidowski gave in his "Biblical stories" (Russ. transl. from Polish: Библейские сказания) book. Kosidowski is almost certainly not the first one to come up with it, though; I do not know who is. Our Longevity myths#Biblical article mentions this explanation, too. --Dr Dima (talk) 22:46, 24 May 2010 (UTC)[reply]
So that means he lived 930 months which would be 77.5 years, that's much more believable, while still being very old for the time. Vespine (talk) 23:04, 24 May 2010 (UTC)[reply]
We may have ended up with some ages in months and others in years. Hunter/gatherers tend to use months, while farmers tend to use years, with herders using a bit of each. Since society of the time had a mixture of farmers and herders, they may have gone back and forth between the two systems. And just as we often omit the word "years" when giving our age, so do those who give their ages in months. Also realize that many books of the Bible were told, retold, written, rewritten, compiled together from multiple accounts, etc., to make the final text. This method results in rather poor quality control and many inconsistencies. This was also common to other books from antiquity, such as the Odyssey and Iliad.StuRat (talk) 00:27, 25 May 2010 (UTC)[reply]
So Enos fathered a son at 90 years old even though he died about 15 years before? (905 months = 75.4166667 years) I never knew the bible discussed sperm preservation and artificial insemination (well not counting the virgin Mary). And to think some Christians are opposed to these sort of things despite having the clear approval of god! Nil Einne (talk) 08:39, 25 May 2010 (UTC)[reply]
There were also likely many mistakes in the Bible, such as confusing two people with the same name, or maybe people just lying about their ages. But a large portion of the ages seems to be around 12 times what would normally be expected, so confusion over months and years is the most likely explanation for most of this. StuRat (talk) 02:37, 26 May 2010 (UTC)[reply]
The modern practice of observing nature, making written records, and thinking freely and critically are recent developments. Galileo Galilei is considered to be the father of this scientific approach to thinking, and he did not do his ground-breaking work until the early 1600s. Prior to Galileo’s new approach to thinking, myth, superstition and intuition were all that was available. People were illiterate and favourite stories were passed by word-of-mouth from parents to children, generation after generation, gathering embellishment along the way. The ancient scriptures, including the Bible, were written by men in that era of myth, superstition and intuition. We should not be surprised when we find things in these ancient scriptures that are not believable. These things should be ignored. Dolphin(t) 23:50, 24 May 2010 (UTC)[reply]
That is not true. Schliemann found Troy based on the Iliad record. Archaeological sites in modern Israel, Palestinian Autonomy, and Jordan are too numerous to even start to mention, and match very well the Biblical record, at least in their location (see e.g. Temple Mount, Tel Megiddo, Tel Hazor, Tel Be'er Sheva). Timelines are far more fuzzy, as expected for the events that took place several hundred years before being written down. Regarding month / year confusion, I recall Kosidowski speaking specifically about people's ages; it may have something to do with how the human age used to be specified 3000-4000 years ago. The day and the month of the Great Flood are indeed specified, as Wavelength has mentioned; but that does not mean that Noah's age is accurately recorded. --Dr Dima (talk) 00:08, 25 May 2010 (UTC)[reply]
I didn't imply that everything found in ancient scriptures is incorrect or unsound. My view is that when we find things in these ancient scriptures that are not believable, we should not believe them. See Scientific scepticism. The alternative, to which User:TASDELEN alludes, is that the things in the ancient scriptures must be correct and therefore we need to construct an explanation that makes them believable. Dolphin(t) 04:38, 25 May 2010 (UTC)[reply]
As someone who believes in the literal truth of the Bible, I'm rather confused by the idea that "most non-religious scholars do not believe that there was a literal single first human" — wouldn't standard evolutionary theory hold that there was a point at which one organism reached the point that it would be classified as Homo sapiens? Nyttend (talk) 05:44, 25 May 2010 (UTC)[reply]
Not really, we have a Most recent common ancestor also Mitochondrial Eve and Y-chromosomal Adam. I don't think you could really pinpoint the origin or Homo Sapiens to one individual. Even if we are commonly descended through ONE of the individuals, there were thousands of other very similar individuals in the same species which just happen not have surviving descendants today. Vespine (talk) 05:55, 25 May 2010 (UTC)[reply]
(edit conflict) Not really. Speciation is a much more fuzzy and fluid concept. We don't really have a hard-and-fast definition of what makes one group of living things a distinct species. Some of the stuff is really obvious (for example, dogs are different than cats), but at the edges it becomes quite fuzzy. For every aspect of the standard "textbook" definition of distinct species, there are exceptions which are common enough to make the definition problematic. There is the Mitochondrial Eve, often cited as the ancestor of all modern humans, but that doesn't make her a single individual which was a unique species different from the other members of her community. After all, she had to be able to mate with the members of her community to have viable offspring; which would make her the same species as those other members. At a temporally zoomed-out view, we can say that the first modern humans developed sometime around, say 200,000 years ago. But its not like on Monday there were no humans, and on Tuesday there suddenly was one. AT any given point, there are a population of fully interbreedable individuals; that is usually the common definition of a species; when two populations drift genetically apart to the point where they are no longer able to produce viable offspring with each other, we generally hold that they are now different species. But its not a binary state; if we go back to the time when the populations became seperated, they likely would be considered the same species for many thousands of years before genetic drift causes them to differentiate. There isn't a single individual which represents the new species. --Jayron32 05:57, 25 May 2010 (UTC)[reply]
Postscript: Found a good link for Nyttend which discusses in more detail what I was trying to explain above. See Species problem. --Jayron32 06:10, 25 May 2010 (UTC)[reply]
See also ring species (and linear species), where there are a number of different communities of a species, each community is slightly genetically different. Each one can breed with its neighbours, but not with the neighbour's neighbour's. If the community in the middle were to be wiped out, then there would be two unique species, albeit very similar to each other. CS Miller (talk) 11:50, 25 May 2010 (UTC)[reply]
Nice and reasonable comments!
Vespine says: "I think shortest possible year that the Earth with life could have is about 345 days". Then, if the velocity of the light has a fixed value, the definition of light-year distance should be changed to be "light-day" or 1000 LD distance, as " Days and years are independent of each other, a planet can have a long day and a short year, or a long year and a short day, there is no correlation...".I understand 1 Earth's day length is innate,is constant while 1 Earth's year length is variable. So, the distance of the Earth to the Sun is variable.GOD has not placed the planets at a fixed distance and let them orbit the Sun at these fixed distances, on a fixed elliptical orbit as said Kepler in 1609.TASDELEN (talk) 10:30, 25 May 2010 (UTC)[reply]
Sorry I'm struggling to understand what you mean by all of that.. Barring any cataclysmic events, these days both the year and the day of the Earth are quite stable. See Stability of the solar system. I was referring to the period during the formation of the Earth or when there might have been other cataclysmic events, not in the recent or even not so recent past. Vespine (talk) 11:43, 25 May 2010 (UTC)[reply]
I meant the nonStability of the solar system; because,as you say,"I think shortest possible year that the Earth with life could have is about 345 days".So, 1 year may be=to 345 days, in an older time. Then ligth-year distance, at that old time should be = actual measurement*345/365; which is impossible.This why "the non-stability" should be considered. TASDELEN (talk) 14:04, 25 May 2010 (UTC)[reply]
No, TASDELEN, you seem to have have misunderstood some of the earlier discussions. Neither the Earth's day length nor its year length are "innately fixed" so you can't define one variable as a constant and then compare another independent variable to it. The only constant is the second, because we have (now) defined it according to another fixed value based on the invariable properties of light and independent of anything to do with the Earth's motions. We extend the defined second to a defined year by simple multiplication, and the light-year is based on that, not on any derivitive of the actually variable day length and/or year length.
The length of the day (defined as noon to noon) varies slightly through the year due to the eccentricity of the Earth's orbit around the sun: its average over the year depends (mostly) on the speed of the Earth's rotation on its axis. This has been gradually slowing since the formation of the Moon around 4.5 billion years ago, due to tidal acceleration (which both slows the Earth's rotation and moves the Moon further away), so as one tracks further back in time the days were shorter and there were more of them in the year, and also the months were slightly shorter (because the Moon was closer and orbited the Earth faster): "620 million years ago: the day was 21.9±0.4 hours, and there were 13.1±0.1 synodic months/year and 400±7 solar days/year", as that last linked article says. However, these changes are very long term, and the day and month lengths a mere few thousand years ago when the accounts preserved in the bible were formulated would not be noticeably different from today's.
The Earth's orbit, and consequently the length of the Earth's year also varies slightly over very long periods due to several factors, but not by any amount significant for everyday purposes (like measuring lifespans) over historical periods; nonetheless we no longer ultimately define any scientific measurements relative to the actual year, but instead to a year derived from the independently defined second. Vespine was alluding to a purely theoretical situation where the Earth would have fewer days (of the current length) in the year by virtue of orbiting closer to the Sun in accordance with Kepler's third law; increased insolation due to the simple inverse-square law would clearly place a lower limit on the proximity, and hence the number of days in the year, for which habitability would be possible.
Note that a light-year is the distance which light travels in a vacuum in one Julian year (astronomy) which is 31,557,600 SIseconds (with each second defined as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom"). This measure of time is not dependent on the length of sidereal year which is not even now precisely equal to the Julian year (astronomy). 124.157.249.129 (talk) 15:05, 25 May 2010 (UTC)[reply]
When I say "innate=constant", I consider Newton's total energy expression: Etot=Ekin+Epot=Ct, where Ekin=1/2*m*Vr^2+1/2*I*w^2. All V=Velocity related values are evaluated according the new second. So, 1/2*I*w^2 is constant, was (innate), today or 4 billion years ago and this represent what we call "day" in Newton's expression. 1 year is the time for 1 cycle of the Earth around the SUN. Practically, we say this time is 365 days. Year's lengths are "not innate" but variable according the distance of the planet to the SUN.(Kepler's period law). As a possibility of 1 year=345 days is considered, I say "light-year" distance has no sense, but ligth-second distance should be defined. Say 3600*second=1 day=innate=Constant. Then we must use Ligth-day or 1000LD distance in astronomy; not ligth-year. Now, coming back to our Adam's 930 years living, it seems that this is possible if we agree on "variable year lengths". Suppose the human life is 100 fictive Earth's years, today. 100 Earth's years=36500 today's Earth's days. If we were living on Saturn, according Kepler's period law, we will live only ....Saturn's years. Are there any old Earth's periods, where Adam has lived 930 cycles corresponding to today's 100 cycles of the Earth around the SUN? That may explain Adam's and others long life. And probably Adam (homo sapiens) has lived at a period where 930*P=36500 fictive days.Then P=39 days/ a cycle. Mathematically this is possible, but physically it looks impossible. Is it really impossible? TASDELEN (talk) 18:53, 25 May 2010 (UTC)[reply]
No, there has never been a time when the Earth revolved around the Sun 9.3 times faster than it does now (which would require it to orbit only about 30 million miles from the Sun, closer than Mercury). In any era that Homo sapiens has existed (no further back than 1.5 million years using the most generous definitions) the year length has been very close to today's value, so shorter actual years cannot in any way explain the Bible's supposed lifespan values. The fact that in the remote past the Earths axial spin was faster, so that there were more but shorter days in the year, is quite irrelevant to this question, as is the way we define the distance we choose to call a light year (which you have misunderstood, please re-read 124.157.249.129's correct explanation above). 87.81.230.195 (talk) 21:24, 25 May 2010 (UTC)[reply]
Most certainly, people back then were not thinking about velocity of photons or even the rotation of the Earth. Most of the stories where these "timing problems" are present are set in a time when people were not much more than hunter-gatherers. How could they measure years and moths? How could anyone of us, without extensive knowledge of astronomy and without the help of the organized society around us know the exact month we are in or your exact age? Especially in a region without observable change of seasons? How could you measure time frames longer than the day based on things that really interest you? Maybe after the harvest seasons of certain plants? Migration patterns of certain animals you hunt? A year could mean pretty much anything, and most stories before the time of Moses are probably set many centuries apart from each other. Besides this, many people assume the language, way of thinking and memes were exactly the same as today. It's like if you write down that you've seen dozens of something, and many centuries later someone reads it, looks up what "dozen" could have meant, does a research about the things you've seen, discovers that their number was not exactly divisible by 12, and reaches the conclusion that you were a big liar. --131.188.3.21 (talk) 22:39, 25 May 2010 (UTC)[reply]
Numerology was common. A lot of the age spans are probably numerological. Clearly, for example, the 500/600 year motif in the story of Noah is numerological. Also, there are probably clues embedded for the use of ancient scholars but hidden from the common people; for example, the math indicates that Noah's father (Lamech) and grandfather (Methuseleh) both died the year of the (fictional) flood, circa 1656 years after creation ... perhaps masking via allegory a more ancient historical story of a dynastic rivalry. (The preceding is from memory; a detail or two may be wrong.) Perhaps, too, "sacred" science was encoded. The oldest figure is Methesuleh; Methuseleh's age, if expressed in lunar months (circa 27.321 days) rather than years, equals the number of years necessary for the equinoxes to precess exactly one degree. Of course, we presume this figure was unknown to the authors. 63.17.33.231 (talk) 11:44, 26 May 2010 (UTC)[reply]
Yes,User:Dolphin51.I want to believe to the Old Testament citations on ages,and I am searching a mathematical model to explain these sentences.I am Muslim=very good Christian of the time of Jesus=believer of Mooses= from the religion of Abraham= God religion.I am sure a mathematical relation should exist between the ages and the periods of the Earth around the SUN.I don't think the periods were constant since the existence of the Earth.A new theory? TASDELEN (talk) 19:03, 26 May 2010 (UTC)[reply]
A correction: 3600seconds*24hours*365,25days= 1Julian year. When (365,25) is a fixed value, the light-year distance has a fixed value. If, or when a year was 345 days will the ligth-year mean the same distance ? Of course, not. Then, ligth-year definition is inappropriate to measure astronomical distances; while I*w^2 is constant, is innate (any question?). This why, I propose the use of light-day or 1000LD distances for astronomical measurements.Otherwise we should agree that from the existence of the Earth until its collision with the SUN (end of the Earth) years have 365,25 days.And in this case never a collision will occur,as 365,25 is the period of 1 cycle of the Earth around the SUN.Periods should change,should go bigger and then diminue (within 5-6 billion cycles) with time. TASDELEN (talk) 20:54, 26 May 2010 (UTC)[reply]
So, I think most people on the science ref desk will not agree with you. It is a fallacy in science to START with a conclusion and then try to fit reality to your conclusion. Yes we agree there are issues using ANY reference point. Even our galactic co-ordinate system has problems with drift over long periods of time. It doesn't matter WHAT you use as a point of reference, it is an issue that needs to be taken into account and scientists understand that, that's all there is to it. Scientists aren't going to change the astronomical scale so that it fits better with an account from the bible. That's not to say it will never change, but I guarantee that won't be that reason. I think this discussion has gone on long enough already. Vespine (talk) 02:11, 27 May 2010 (UTC)[reply]
I think,I find a math which fit the physics: Newton's law F*dt=m*dv. From this physical law, I will deduct Bible's "Adam 930 years of age". Will this reasoning be a fallacy? You will decide.
F*dt=m*dv means F*r*dt=m*r*dv ( energy conservation equation). So, we write
1/2*m*Vr^2+m*gr*r+1/2*I*w^2=m*r*dVr (total energy with g variable;and Vr=radial velocity)
This is a differential equation
dr^2+K*dt^2=2*r*d(dr)
with solution
r=-a*t*(t*tmax)+K where K=2*gr*r+I*w^2/m=-a^2*tmax^2/(1+4*a)
On Cartesian, the graph of (r) is a parabola.
On Polar this graph is a cardioidal looking spiral: billions of spirals. Expanding then after compressing; with a max.point, only one max.point.
This is the shape of the orbits. No sign of ellipse, no sign of aphelion, no sign of perihelion.A new theory for "orbits" !!!!.
Expansion and compression of the spiral ring's amplitude means "variable cycling period".In this concern,the creation of the Earth is due to a "small bang" of the SUN which ejected the planets and other celestial bodies of the Solar system.The "variable cycling periods" is due to the constant,innate, I*w^2.That means Vp perpandicular to Vr is "invariable". Then,"Adam's 930 cycles" may fit a period of P*930=36500 days (considering today's 100 cycles for Adam life).That is P=39 days/a cycle.And this period existed 4 344 656 600 cycles ago,approximately.According this evaluations "homo sapiens" should have existed so long time ago.TASDELEN (talk) 07:41, 27 May 2010 (UTC)[reply]
So instead of taking the knowledge we have of how long a human can live and turning it on its head to fit your conclusion, you're going to take all of cosmology and turn it on its head instead? Why bother? Just say Adam lived 930 years, you only have to break one rule then instead of rewriting the entire solar system; and God did it anyway, so what's the problem? You seem exhibit very little faith for someone trying so hard to reconcile God's "actions". I've said about all i have to say on this subject, if you want to debate this subject more I suggest you seek out one of the many discussion forums around the internet as a more appropriate place for these kinds of discussion. If you have any more specific questions about planetary orbits or something else sciency, feel free to start a new section and ask away. Vespine (talk) 00:45, 28 May 2010 (UTC)[reply]
ThanksVespine. Your's "There's no evidence that the Earth shuffled around or changed places since the formation of the solar system, there may have been some catastrophic events which changed the year a bit, but there's some decent evidence that the Earth has been at least in the Habitable zone, since life arose anyway" is a canonic sentence. As an alternative, I proposed Newton's F*dt=m*dv which gives r=-a*t*(t*tmax)+K (may be wrong!) from where I evaluated mathematically (not physically) the age of ADAM. That means "Earth is changing places" is a non-canonic statement, and it is difficult to change the perception of the community with such reasoning.It was nice to communicate with you.Thanks again. TASDELEN (talk) 21:22, 28 May 2010 (UTC)[reply]
I think we have shown elsewhere that your mis-derivation of "spiral orbits" (in contradiction of Kepler's laws and the observations of Tycho Brahe) just don't make sense, so they cannot explain varying "years". There is quite a lot of science that it is worth challenging, but I don't think you have the remotest hope of creating a new mathematics of orbital motion. Too many mathematicians have understood the derivation, and too many observations have confirmed that they are valid. Sorry. Dbfirs 15:32, 29 May 2010 (UTC)[reply]
You have shown nothing. You did not considered my derivations.(even they may be mis-derivations). You did not pointed out the false steps of my derivations. You just copy-pasted ellipse article from WİKİ, as a proof. According me Wiki's proof of orbital motion is wrong, since Vp perpandicular velocity to Vr (radial velocity) is asumed to be variable, and I say constant. If you prove that Vp velocity is variable, then Newton's energy conservation expression should be refused. You are refusing Newton's F*dt=m*dv. Sorry. TASDELEN (talk) 18:59, 29 May 2010 (UTC)[reply]
And I copy-paste the following discussion paragraph,for your control:
No Tango.The statement (1/2*m*Vr^2+m*gr*r+1/2*I*w^2=m*r*dVr) is correct as it is the energy conservation expression. With the following correction (K/dt^2=m*gr*r+1/2*I*w^2) we write:
1/2*m*(dr/dt)^2+K/dt^2=m*r*d(dr/dt)/dt which is,after simplification:
r'^2+2*K/m/dt^2=2*r*r" a differential equation (with all the terms of the same size,same order) having the solution:
r=-a*t^2+a*t*tmax+K where K=-a*tmax^2/4=Constant.In fact:
dr/dt=r'=-2*a*t+a*tmax
d(dr/dt)/dt=r"=-2*a
r'^2=4*a^2t^2-4*a^2*t*tmax+a^2*tmax^2
2*r*r"=-4*a*(-a*t^2+a*t*tmax+K)=4*a^2*t^2-4*a^2*t*tmax-4*a*K which is ending by:
4*a^2t^2-4*a^2*t*tmax+a^2*tmax^2+000000=4*a^2*t^2-4*a^2*t*tmax-4*a*K and after simplification
a^2*tmax^2=-4*a*K and K=-a*tmax^2/4 (as I have posed=Constant).
All this has one meaning: [r=-a*t*(t*tmax)+K] and the graph of this equation is a spiral on Polar plane.Not an ellipse.I think Kepler's laws of planetary motion#Derivation from Newton's laws should be revised for (Derivation) and should not be copy-pasted as icon. I insist: either Newton's law indicates my solution or the solution of Zunaid. I need mathematical proofs, confirmations, and not discouraging sentences like they don't have a grasp of English. What about your Turkish? Meanwhile, a difficult question about Kepler's area law: do you believe to the derivations on Wiki? Is Vp perpandicular velocity to Vr (radial velocity) variable or constant? Wiki says: variable. I say constant. Thanks.TASDELEN (talk) 13:10, 28 May 2010 (UTC).TASDELEN (talk) 08:10, 30 May 2010 (UTC)[reply]
No comments from Wiki administrators? Which administrators are refusing Newton's law of F*dt=m*dv? No one ? Very good, then consider please Wiki's derivations correctness about the orbital motion of the planets: see if Vp is constant or not. According me Vradial is variable, Vperpandicular is constant. And a simple proof of this is as follows:
1/2*m*V^2+m*gr*r+1/2*I*w^2=Ct (total energy equation with variable g,and innate I*w^2)
(Vr1^2+Vp1^2)+2*m*gr1*r1=(Vr2^2+Vp2^2)+2*m*gr2*r2 (equality at#1 and #2 position)
Vp doesn't change the equality of the energy conservation equation,So
Vr1^2+2*m*gr1*r1=Vr2^2+2*m*gr2*r2 and this means Vp1=Vp2=Vpn=Ct
And saying so, dVp/dt=0
Wiki says d(r*Vp)/dt=0 and deducts "areas equality laws". Wiki is wrong. Administrators should comment this math. The orbit of the planets is a spiral situated on a paraboloid surface along the trajectory of the Sun in its galaxy, expanding and then compressing.For this look please to some galaxies photos from Nasa. New theory on cosmology !!!!No reference,no back ground,but Newton's laws derivations.TASDELEN (talk) 22:01, 31 May 2010 (UTC)[reply]
TDS
Say one has a geophysical electric log with data for SP, short number (16), long number (64), and what one wants to do is to calculate/estimate the TDS (Total dissolved solids) -- water quality -- from that data. How does one go about doing that? Killiondude (talk) 22:14, 24 May 2010 (UTC)[reply]
This link may be of some help, although it points out that it can be used in this way provided that the analysis is tied closely to local water chemistry measurements. Mikenorton (talk) 19:32, 25 May 2010 (UTC)[reply]
Consider a satellite moving at 3.87 km/s - how much is the clock aboard the satellite affected by special relativity per day?
The calculation I did was meaning that the clock aboard the satellite falls behind by about 7.2 microseconds per day. Could someone please verify that this is the correct approach?220.253.221.60 (talk) 00:32, 25 May 2010 (UTC)[reply]
Could you give us the rest of your approach? It is difficult to know if it is right based on just the final answer. (I could try and calculate it myself and see if I get the same answer, but even if I do, that doesn't mean your approach was right - you might just have been lucky.) --Tango (talk) 00:54, 25 May 2010 (UTC)[reply]
(ec) It's fine, except that a day is 86400 seconds long, not 86500, and you can't realistically ignore general relativity in this situation. (Also, you're comparing your satellite clock to a clock "at infinity". If you wanted to compare to a clock on the surface, you'd have to take into account that surface clocks also move at up to 0.5 km/s relative to a nonrotating frame, depending on latitude.) -- BenRG (talk) 00:55, 25 May 2010 (UTC)[reply]
Ah, that's why I wasn't recognising the method! Now I see what the method is! --Tango (talk) 01:04, 25 May 2010 (UTC)[reply]
Global Average Annual Temperature limits
How low/high can the Global Average Annual Temperature drop/rise before it irreversibly spirals into either an snowball effect or a runaway greenhouse gas effect.24.78.167.139 (talk) 01:00, 25 May 2010 (UTC)[reply]
I don't think the scientific community has reached a consensus on that. I'm not sure there is even a consensus that either of those things would happen at all. --Tango (talk) 01:12, 25 May 2010 (UTC)[reply]
The problem with climate change is that the current climate system has been relatively stable for a long period of time. Historical records of climate show that in transitions between different stable climate states, the system becomes highly chaotic and unpredictable before establishing a new equilibrium. So, while the current rate of carbon emissions is likely to lead to a warmer, on average, equilibrium climate conditions, the path to that new equilibrium state is likely to be a wild ride, and very unpredictable. Picture several centuries of unpredictable and wild climate swings, and that is part of the big problem. Its not that we can predict what will happen that is the problem. That would actually be less of a problem, because we could at least prepare for it even if we couldn't stop it. Its that we a) know its going to be crazy and b) can't predict what kind of crazy its going to be. The problem is that this is a complex problem which has been reduced by the popular media to "global warming" or "global cooling". Then people here scientists making both predictions, and think "they don't know what they are talking about, so we can ignore whatever the scientists predict." It might be better to think of it as "global climate clusterfuck." --Jayron32 01:30, 25 May 2010 (UTC)[reply]
Y'know, climate change could go different ways in different parts of the world, too (for instance, we could have global warming in Europe and Africa but global colding in North America, among many other possibilities). FWiW 67.170.215.166 (talk) 06:53, 25 May 2010 (UTC)[reply]
You're confused about the meaning of the word 'global'. 67.243.7.245 (talk) 19:14, 25 May 2010 (UTC)[reply]
I think there is a consensus that if it somehow got so cold that the oceans froze over down to the equator, the resulting Snowball Earth state would be stable until CO2 built up to extremely high levels. I think there is also a consensus that a runaway greenhouse is not a real possibility -- CO2 levels have been over ten times higher in the past without producing such an effect. Looie496 (talk) 06:56, 25 May 2010 (UTC)[reply]
So there is no maximum temperature, and there is no minimum temperature??24.78.167.139 (talk) 07:12, 25 May 2010 (UTC)[reply]
Not so. There are probably (though not certainly) both, but we don't yet know what they are, and other factors beyond average global temperature (such as atmospheric composition, continent distribution and biosphere feedbacks) also have influence through multiple interactions more complex than we yet understand. Our current studies are focussed mainly on changes and states that are much less extreme, but which nonetheless would have serious effects on human global infrastructures and civilisation (such as sea-level changes). Looie496's second point (on the runaway greenhouse) related only to CO2 levels, but ultimately increased insolation due to the long-term brightening of the Sun will almost certainly cause one, and one way or the other will raise the average global temperature way above survivability. 87.81.230.195 (talk) 13:33, 25 May 2010 (UTC)[reply]
The utter maximum could easily be close to the situation on Venus - 460°C!! Venus is a little closer to the sun - but not anywhere near enough to account for the difference. But the truth is that we don't know.
There is certainty in a short term (several years) rise in average global temperature and a rise in ocean levels...we're actually measuring that happen and seeing it correlate to CO2 levels. But if it levels out - and where it levels out is totally unknown.
Firstly because we can't predict irrational human behavior...the degree to which we turn down the CO2 production rates is sensitively dependent on crazily unpredictable things like the reaction of the US public to a health-care bill pushing out the time when the climate change laws can be discussed and whether some accident in the gulf of mexico produces an oil spill and a knee-jerk reaction to pro-"green" agendas.
Secondly, there are feedback loops - both positive and negative built into the system. Some things (like the melting of the polar ice causing the shiney white reflective surface to be replaced by dark green, heat-absorbing ocean) mean that as things get hotter, so those systems make the world hotter still - positive feedback - a 'runaway' effect that's impossible to stop once it gets started. Other things (like the increase in CO2 levels causing some kinds of plants to grow faster - enabling them to absorb yet more CO2) have the opposite effect - negative feedback.
When you get dualling run-away systems, the result is exceedingly hard to predict. If you turn on both taps on your bathtub and pull the plug out - will the bath stay more or less empty or will it eventually fill up and overflow? It's hard to guess. What if you install a device that opens the faucets up more and more the deeper the water gets? And this is a vastly over-simplified analogy. There aren't two systems (drain and faucets) fighting each other, there are hundreds of systems - and many of them have that property of positive feedback: "the worse things are, the worse they'll become".
The smart money says this: Even if the findings are 'iffy' and there is only (let's say) a 15% chance of making the planet essentially uninhabitable and an 85% chance that it's all just bad science - can we really just ignore that risk? Would you be prepared to risk the future of your child's life on the roll of a single dice? If it comes up '1', they shoot your kid...and everyone else's kid for good measure? If that was the choice then wouldn't you do absolutely everything in your power to avoid rolling that dice? The science is easily 15% reliable...probably more like 85% reliable. Roll a dice, if it doesn't come up '6' they kill your kid. Why are you waiting for a certain answer? SteveBaker (talk) 20:21, 25 May 2010 (UTC)[reply]
What makes you think that climate change has the slightest possibility of making the planet "essentially uninhabitable"? Even scientists who agree that global warming is happening don't make such outrageous claims anymore -- only Al Gore still makes these kinds of statements. 67.170.215.166 (talk) 02:04, 26 May 2010 (UTC)[reply]
I think you mean human-caused climate change. The earth itself is capable of some pretty destructive stuff all on its own, without humans. There have been some catastrophic geologic events in the past, and there's nothing to say something like the YellowstoneSupervolcano couldn't happen again, say, tomorrow. Look at the effect of the Mount Tambora eruption on climate (the Year Without a Summer, and imagine an event several orders of magnitude larger. Such eruptions exist in the geologic record. There are lots of ways the climate could change to make the Earth essentially unlivable. It is unlikely humans could do anything like that, but that isn't to say that the Earth could not become unlivable. The article Risks to civilization, humans and planet Earth contain some overview of this. --Jayron32 02:19, 26 May 2010 (UTC)[reply]
I have trouble buying anything in the foreseeable future completely destroying humans. At this point, we have the technology to survive in some pretty extreme conditions. I can imagine something wiping out 90+% of people (heck, we can even do that with nuclear weapons), but killing off everyone would be hard, even for nature. Buddy431 (talk) 03:55, 26 May 2010 (UTC)[reply]
Brewing yeast and fructose
What is the difference between yeast metabolism of glucose and fructose? Our yeast article only mentions fructose once. Specifically, I'm curious in brewing yeast whether fructose has the same conversion rate as glucose. Shadowjams (talk) 02:07, 25 May 2010 (UTC)[reply]
Most yeast uses glycolysis to convert sugars into energy (and alcohol). One of the early steps in glycolysis is the conversion of glucose-6-phosphate to fructose-6-phosphate. This reaction is easily catalyzed, and goes back and forth freely (glucose-6-phosphate isomerase is not a control point in glycolysis). The only difference between glucose and fructose utilization would be differences in efficiencies between going from free glucose to glucose-6-phosphate and free fructose to fructose-1-phosphate. -- 174.24.200.38 (talk) 04:32, 25 May 2010 (UTC)[reply]
Thank you for that, but I think glycolysis differs greatly from fructolysis and fructose-6-phosphate is quite different from molecular fructose. Do yeast have a fructolysis pathway? Shadowjams (talk) 05:37, 25 May 2010 (UTC)[reply]
Cats and newborn/infant humans
My wife and I have 4 cats and we are planning on adding a human soon. Could someone please help me find reliable sources regarding precautions and practices for newborns and cats? I am not asking for medical advice, I'm asking for help finding government health guidelines and the like - there is certainly a distinction. I'm already aware of toxoplasmosis - but that's the only reliable and well-sourced issue I can find. Help? 218.25.32.210 (talk) 03:19, 25 May 2010 (UTC)[reply]
The medical professionals you consult at various stages during the pregnancy will be able to give you advice on pets or at least tell you where to find that advice. I think they can do that better than we can. --Tango (talk) 03:22, 25 May 2010 (UTC)[reply]
When I was a baby our cat (Kitty Fisher) used to sit in my pram and guard me :) DuncanHill (talk) 07:40, 25 May 2010 (UTC)[reply]
Cats rock, but ask your doctor. The toxoplasmosis issue is relevant, but perhaps there are other issues. Shadowjams (talk) 10:13, 25 May 2010 (UTC)[reply]
Antenatal classes warned us on the risk of accidental suffocation from cats thinking babies faces were nice warm places to sit. A cot net or exclusion was advised. --BozMotalk 10:41, 25 May 2010 (UTC)[reply]
Yeah, there are documented cases of that, with babies at least as old as 3 months. EverGreg (talk) 11:19, 25 May 2010 (UTC)[reply]
A study found that children who were exposed to cat-allergenes in the household dust at age two, had an increased risk of developing asthma at age 10. So cleaning would be important. cleaning, vacuuming mattresses and keeping the cats away from the bed would be a precaution. (This is from the PhD thesis of R.J. Bertelsen: "The indoor environment and childhood allergic disease; the importance of allergens and microbial components" [8])
This goes hand-in-hand with the suffocation issue. Never let the cat have access to a sleeping child and keep it out of the bedroom completely.
Confusingly, other studies have shown the opposite effect of cats and allergies, so the issue is not completely settled, though this appears to be one of the more thorough studies.
There are also issues of cat-psychology. The cat could get jeleaous or stressed and react by biting the baby or defecating indoors. Some recommend to famliarize the cat with the baby, by letting it smell the baby for instance. EverGreg (talk) 11:19, 25 May 2010 (UTC)[reply]
My sister didn't have a cat at home until she was about 3 - she is asthmatic. I had a cat in my pram from as soon as Kitty could get in there, and I'm not asthmatic. When she had her kitten (Pussy Simpkins) she'd bring Puss in by me too. DuncanHill (talk) 22:24, 25 May 2010 (UTC)[reply]
Nothing personal but I would strongly advise against this kind of anecdote. This is one of the reasons we don't give medical advice, everyone has an anecdote but for all we know, your and your sisters asthma (or lack of) could very well have nothing to do with cats. The OP was asking where to find information, not for personal experiences. Anecdotes are what superstitions, pseudoscience and quackery thrive on. Vespine (talk) 22:50, 25 May 2010 (UTC)[reply]
Vespine is right. --Tango (talk) 23:41, 25 May 2010 (UTC)[reply]
Vespine is absolutely right, we all know people who lived to old age despite smoking and not wearing seat-belts, but those stories are not an appropriate answer to a question about whether those things are good ideas. APL (talk) 18:47, 28 May 2010 (UTC)[reply]
You should also take in to account the personality of the cats. Babies cry, whine to be fed constantly, and puke at inopportune moments. Some cats react badly to this. We were lucky in that we had a Siamese which considered all that to be perfectly normal behaviour. As EverGreg mentioned above, jealousy can be expressed in all kinds of ways; during the first meeting, you'll want to be extremely close by to immediately correct any violent behaviour towards the infant; they'll need to learn right off the bat that attacking the new naked "cat" is unprofitable. Contrary to popular belief, cats can understand a basic social hierarchy, so long as it is presented clearly. This site suggests that some cats may "spray" in response to the new arrival (in an attempt to cover the new scent). I'm not sure what kind of precautions you can take with that, but if you've been thinking about replacing your carpets with linoleum, now might be a good time. :-) Matt Deres (talk) 23:24, 25 May 2010 (UTC)[reply]
Cats Protection has published a leaflet Cats and children (PDF). This publication by UK government website Teachernet, advises the use of cat nets to prevent suffocation, as mentioned above. There is Cats and babies - can they co-exist? (although it does contradict the cat suffocation thing). This article is about psychologically preparing your cat for a new arrival. I also found this and this which provide some more of the same advice. I had a trawl through some UK government websites, but haven't found anything more substantive so far. --Kateshortforbobtalk 20:08, 26 May 2010 (UTC)[reply]
Future computer (from IP 117.197.246.107)
if in future somebody makes a future predicting device/computer , what would be its concequences??? —Preceding unsigned comment added by 117.197.246.107 (talk) 10:03, 25 May 2010 (UTC)[reply]
This has been considered and there are results in computer science that state that such a machine is impossible. Consider: Machine #1, able to predict the future, tries to predict what will be going on inside a house. In that house there is machine #2 which can also predict the future, but it predicts the future of machine #1. That is, it knows what machine #1 will predict and then it does something that breaks with that prediction, invalidating the result of machine #1. Put in another way, a machine can't predict the outside world because you can't cram all the complexity of the outside world into a computer. EverGreg (talk) 11:03, 25 May 2010 (UTC)[reply]
Perfect future prediction being available creates causality problems, so they couldn't exist unless we are massively wrong about the way the universe works. For example, imagine that this computer predicts whether I'm going to say "apple" or "orange" next. In order for the prediction to work, I can't look at the prediction and do the opposite, but that's the very thing I want to do!
Interestingly, there's a a similar argument that the easier-sounding problem of halting problem is also unsolvable. If you could write a program (call it "H") to determine whether another program will halt or not, you could write another program that runs H on itself, and obstinately does whatever H said it wouldn't do it. It may seem like a silly trick, but this kind of thing comes up all the time in computer science. Paul (Stansifer) 12:00, 25 May 2010 (UTC)[reply]
Perfect prediction is impossible since quantum mechanics tells use the universe isn't deterministic. Approximate prediction we already have in various ways (eg. weather forecasting, as already mentioned). --Tango (talk) 16:01, 25 May 2010 (UTC)[reply]
We have computers which predict the future! They predict the weather every day. They compute the orbits of satellites and predict where they will be. They predict solar eclipses, predict winners in baseball games, predict population growth for traffic studies, predict where an artillery shell will land, etc. anonymous6494 16:00, 25 May 2010 (UTC)[reply]
Right. You can predict "future" (trajectory) of a macroscopic system, with accuracy that decreases for longer time. If the dominant interpretation of the quantum mechanics is correct, however, you can not predict the outcome of a measurement unless the system is in an eigenstate of the operator involved; you can only predict the probabilities of all possible outcomes, but not the outcome itself. Even when you disregard the quantum-mechanical "complications", in classical mechanics most many-body systems exhibit "deterministic chaos", which essentially makes the long-term prediction of future an exercise in futility; I can go into more details if you want me to. --Dr Dima (talk) 19:40, 25 May 2010 (UTC)[reply]
They don't "predict" the future (check your dictionary!) - that would imply that they always get the answer 100% perfectly right! They estimate the future...with varying degrees of success - that's certainly possible.
Wrong. Predictions always have a finite accuracy, and are never implied to be 100% correct. That is how a prediction is defined. See Prediction interval. --Dr Dima (talk) 00:42, 26 May 2010 (UTC)[reply]
The problem with perfectly predicting the future is also a matter of thermodynamics. The computer requires energy in order to perform calculations - and that energy gets turned into (mostly) radio waves and heat. The amount of radio/thermal energy and the direction it's radiating in depends entirely on how those calculations turn out - roughly, on how many bits have to be flipped. Simplistically: if the answer to a simple piece of arithmetic changes the value in a one-byte memory location from 0 to 127 (which in binary is from 00000000 to 01111111) then the computer will consume seven times more energy than if the answer to the calculation had been just one bigger and changed the memory contents from 0 to 128 (ie from 00000000 to 10000000). Since the energy output by the computer as a part of its calculations goes out into the environment, it actually affects the very future that the computer is trying to predict (not by much...but think "butterfly effect"!). That means that to perfectly calculate the future, the computer would have to be able to perfectly calculate the effect of it's own energy output...energy that will come about from a calculation it has yet to perform! But doing that requires that the computer perform those very calculations that it has not yet performed in order to know what data to feed into those very same calculations! Hence there is an infinite regress and the computer cannot possibly predict the future accurately because any calculation it does in order to perform that prediction changes what the outcome should be. SteveBaker (talk) 19:52, 25 May 2010 (UTC)[reply]
And if you can't take even a tiny bit of Tom Cruise, you can just read "The Minority Report" by Philip K. Dick (first published in 1956!). SteveBaker (talk) 14:10, 26 May 2010 (UTC)[reply]
What's the Asimov story that's a bit like Minority Report, except that instead of arresting people for crimes they haven't committed, Multivac gives action to prevent them from committing it with no further action taken (like calling the person and telling them not to do it!). I think the action of the story was the computer trying to kill itself while staying within the bounds of its programming, by predicting that someon would try to kill it. 212.183.140.2 (talk) 19:38, 26 May 2010 (UTC)[reply]
The closest I can think of is The Evitable Conflict. That does sound like a story Asimov would write, though. Paul (Stansifer) 02:34, 27 May 2010 (UTC)[reply]
I remember the story Mr. 212's talking about, but unfortunately, I can't remember the title, or what collection(s) it's in. Buddy431 (talk) 03:31, 27 May 2010 (UTC)[reply]
Better than nylon at doing what? Both Tyvek and nylon have many uses. Dismas|(talk) 10:20, 25 May 2010 (UTC)[reply]
It can be assumed that unless tyvek and nylon are controlled by regulation, that they would not both continue to be on the market, unless each had a distinct niche. Nylon has been widely made for decades, therefore it's almost certain that tyvek, a newcomer, has some inherent advantage. 24.130.145.253 (talk) 04:18, 26 May 2010 (UTC)[reply]
list
please list these in order of solvent strength. 91% alcohol, pure acetone, 3% peroxide, kerosene, turpentine, 5% vinegar, pure lemon juice (citric acid) household ammonia, 10 % hydrochloric acid, 10 % nitric acid, , ethyl ether, chlorine bleach —Preceding unsigned comment added by Tom12350 (talk • contribs) 11:10, 25 May 2010 (UTC)[reply]
Solvent strength for what? sugar, salt ?87.102.85.123 (talk) 12:20, 25 May 2010 (UTC)[reply]
Yeah it depends on what you want to dissolve: food, bacteria, plastic, goo, salt, etc. etc. --Chemicalinterest (talk) 13:52, 25 May 2010 (UTC)[reply]
For copper the 10% nitric acid is strongest, a mixture of the 3% peroxide and 10% hydrochloric acid is next, then bleach, then ammonia. --Chemicalinterest (talk) 13:53, 25 May 2010 (UTC)[reply]
Kerosene and turpentine are oils, they will mix with other oils.
Depending on the type of oil Acetone .. ethyl ether .. 91% alcohol will have roughly the same de-oiling properties, alcohol being slightly weaker, or possibly innefective for heavier non vegetable oils.
Citric acid is a well known degreaser, vinegar to a lesser extent.
The other acids and ammonia may be slightly better than pure water. Non will have any true de-oiling effect. Neither chlorine bleach or nitric acid can be recommended and are potentially unsafe.
end
In general hot water, or water with detergent will be more effective than all except ether/acetone. Thick oils may not even dissolve in a ether acetone mixture, but hot detergent solution will work in this case.77.86.125.207 (talk) 18:19, 25 May 2010 (UTC)[reply]
An oil can still be a solvent. Edison (talk) 22:47, 25 May 2010 (UTC)[reply]
Acetone is a common choice for removing oil from surfaces. Reasonably pure acetone will leave no visible residue, and is fairly safe except for fire hazard. Alcohol is also fairly safe, but less effective for oil / fat, and is also a fire hazard. Commercial detergents (say, a liquid for manual dish-washing) should work well, too. What kind of surface are we talking about? Acetone may damage plastic surfaces. And don't even think of using nitric acid or (di)ethyl ether. --Dr Dima (talk) 20:01, 25 May 2010 (UTC)[reply]
i dont want to use a detergent. i know that Kerosene and turpentine are oils. but they are also solvents. where do they rank in that list in terms of strength? —Preceding unsigned comment added by Tom12350 (talk • contribs) 07:01, 26 May 2010 (UTC)[reply]
The relationship between the passage of time for a stationary object and the passage of time for a moving object
My understanding is that the relationship between the passage of time for a stationary object and the passage of time for a moving object is given by the formula
In this formula, which variable represents the passage of time for the stationary object (i.e. or ) and which one represents the passage of time for the moving object?--Wikinv (talk) 12:45, 25 May 2010 (UTC)[reply]
In relativity, it's not possible to distinguish between which object is moving and which is stationary. To object A it may appear that it is stationary and object B is moving. To object B, it may appear that it is stationary but A is moving. So we can only talk about the passage of time in our frame of reference, and the other that appears to us to be moving. I beleive that refers to our frame of reference, and refers to the frame of reference that we see to be moving. See Time dilation --Phil Holmes (talk) 16:30, 25 May 2010 (UTC)[reply]
Here's what that equation really means: if you have a bunch of clocks that are at relative rest ("comoving") and all synchronized in a certain way ("Einstein synchronisation"), and you have one clock that moves at a speed v relative to all the others (which I'll call the wandering clock), and the wandering clock passes two of the other clocks at different times, and Δt is the time ticked off by the wandering clock between those encounters, and Δt' is the difference between the readings of the two clocks it encountered, then that equation gives the relationship between Δt, Δt', and v. Don't try to remember the primes; just remember that the wandering clock always records the shorter time ("time dilation"). -- BenRG (talk) 20:41, 25 May 2010 (UTC)[reply]
...So does that mean that it takes less time for a traveling object, "C" to go from stationary objects "A" to "B" than it does for stationary objects "A" and "B" to stand still, i.e., "A" and "B" would have more ticks than "C"? 71.100.8.229 (talk) 10:24, 26 May 2010 (UTC)[reply]
Now that a semi-artificial microbe has been created, would any microbe, artificial or otherwise, be able to survive and grow on Mars? And could they help to terraform Mars, by changing the composition of the (thin) atmosphere, or raise temperatures by the greenhouse effect for example? 92.28.244.102 (talk) 14:18, 25 May 2010 (UTC)[reply]
In theory, sure. There's no reason such an organism would need to be artificial, though: current techniques could be used to encourage an existing organism to adapt to the Martian climate. As for how much change such organisms could make, and how long it would take them to make it, that's for a scientist of a different sort to answer. – ClockworkSoul 14:32, 25 May 2010 (UTC)[reply]
As I recall, one of the major problems with Mars is the lack of a magnetosphere, and the consequent exposure to solar winds. DuncanHill (talk) 14:48, 25 May 2010 (UTC)[reply]
There is a difference between spores surviving and a microbe actually being able to grow. Nothing we know of would be able to grow on the surface of Mars without a major assist. It is barely possible that there are deep subsurface environments where liquid water exists and microbial growth could occur -- but since the crust is solid and therefore lacks mixing, any such life would quickly exhaust its resources. Looie496 (talk) 15:41, 25 May 2010 (UTC)[reply]
Radiation is not that much of a problem. If our article on Terraforming of Mars is right, even humans without shielding can survive Mars radiation levels for years. Microorganisms should be doing just fine with this. Of course, a direct hit by a coronal mass ejection is a different story. One would imagine that the said microorganisms live in the H2O and CO2 ice-rich top layer of the "soil" near the polar caps, and reproduce during summer when the temperatures go up and the ice starts to melt/sublimate. For the winter they would either freeze or form spores or endospores. The hope is mostly to increase Mars albedo in the visible range, so the surface is warmer; and, to a lesser extent, to increase Mars atmospheric pressure. I would not be surprised if many of the extant terrestrial microorganisms can survive dormant on Mars for years or longer. Coercing them to effectively grow and multiply is much harder, though. Bear in mind that the spores from Earth are probably present on Mars already, and likely in large quantities. Earth atmosphere "leaks out" into space due to the interaction with solar wind, so small airborne particles are likely to be carried with it. Some of these particles can (and will) eventually get deposited on the surface of Mars. The fact, however, is that we have not conclusively detected any microorganisms on Mars so far. This may be because (1) we did not look hard enough or in the right places, (2) the microorganisms are all dead by the time they reach the surface of Mars (e.g. killed during re-entry), (3) The conditions do not allow for any of them to multiply. As for bringing the bioengineered ones from Earth - it would me far more appropriate to thoroughly search for the local ones first. --Dr Dima (talk) 18:33, 25 May 2010 (UTC)[reply]
There is also the fact that aggressively introducing microbes to the surface of Mars could destroy any life/evidence of life previously extant on mars, or at least complicate the identification of it, so we'll probably be studying the surface of mars for at least a few more decades before anyone with the means seriously thinks about terraforming it. 210.165.30.169 (talk) 03:02, 26 May 2010 (UTC)[reply]
Effective Max speed of the international space station during interplanetary travel.
Force of drag: I want to set this equal to the force of the stabilizing engines, but I cannot find this information.
Reference Area: Since the main engines are in Zvezda, I'll use height and width instead of length for the area to give me: 108.5 m * 20 m = 2170 m^2
So can anyone help me find the force of the main engines and calculated the mass density of interplanetary medium? —Preceding unsigned comment added by Anythingapplied (talk • contribs) 15:06, 25 May 2010 (UTC)[reply]
You can ignore drag, it won't be a significant factor. It's not going to stop accelerating when drag balances thrust, it's going to stop accelerating when it runs out of fuel. I don't think the ISS's own engines would be enough to even get it out of orbit - they use the engines of docked spacecraft just to boost the orbit a bit, they would need to attach much bigger engines to get it to escape velocity. --Tango (talk) 15:58, 25 May 2010 (UTC)[reply]
But the ISS is scheduled to get a VASIMR engine. This has much better specific impulse than old-fashioned chemical rockets, so it will certainly change things. --Stephan Schulz (talk) 17:04, 25 May 2010 (UTC)[reply]
What if fuel were unlimited? I've been told by others that drag is insignificant, but at some speeds, it has got to start being significant (say 1/100 the speed of light?). Maybe you have to start getting into relativistic speeds before it matters, but I'm still really curious to what would happen if you plugged in all the right numbers... how fast you could get going? So assume fuel is infinite and that the solar system is infinite stretching on at 5 particles / cc. How fast could you get going? I guess I would like to see first hand the results of the equation that say the drag is insignificant, but am having trouble finding a complete set of numbers to plug in. Anythingapplied (talk) 18:41, 25 May 2010 (UTC)[reply]
My guess (but we await an expert on this) is that even at speeds approaching the speed of light, the drag force will still be less than that of the (reasonable powered) thrusters, so, with infinite fuel, the energy acquired (but not the velocity of course) can increase without limit (assuming that time is also infinite). As a simple, back of an envelope calculation, one could assume that the number of particles emitted by the thrusters would have to be many times greater than the number of drag particles encountered. The number of times greater would depend on the speed at which the thrusters emit particles. Dbfirs 21:50, 25 May 2010 (UTC)[reply]
I think the ISS would be destroyed by the interplanetary medium ablating the hull (which is one of the biggest problems with interstellar travel - if you go fast enough to make the trip a reasonable length, the interstellar medium destroys you) before the drag became an issue. If we ignore that, we should be able to work it out, but it would require relativistic calculations. I'll let somebody else do that. --Tango (talk) 23:17, 25 May 2010 (UTC)[reply]
Ah yes, I hadn't thought of that. Since we are dealing in unrealistic infinities, should we assume that the hull is infinitely strong? I assume that magnetic field shielding becomes ineffective at these speeds? Dbfirs 01:29, 26 May 2010 (UTC)[reply]
[citation needed]. How much interplanetary spaceship-destroying "interplanetary medium" is there per cubic kilometer, exclusive of asteroids? Why haven't all the previous interplanetary probes been destroyed by it? Edison (talk) 05:24, 26 May 2010 (UTC)[reply]
Because none of them travelled at relativistic speeds. --Tango (talk) 11:14, 26 May 2010 (UTC)[reply]
75% of the universe is hydrogen, so 5 particles / cc is essentially 5 amu / cc = 8.3×10−21 kg / m-3. It is pretty trivial to show that this density results in negligible drag for anything less than highly relavitstic speeds. Dragons flight (talk) 09:15, 26 May 2010 (UTC)[reply]
Agreed, but there will come a time, even with the most powerful thrusters, when the momentum of these "drag particles" (apparently approaching at a speed just a whisker short of c), will be greater than the momentum of the particles ejected by the thrust jets, so my guess above was wrong. There will always be a limiting speed, just short of c. Could an expert on relativity please check my understanding of the situation?Dbfirs 16:12, 27 May 2010 (UTC)[reply]
Moon
Given the level of technology available in 1959, would it have been technologically possible to send people to the moon, and return them? Or to put it another way, were the materials, technology and understanding of space travel developed enough at that point? I know the moon landing is considered fact (I don't want to get into a big discussion about that) and you could just say "yes" and post the wikipedia article as proof, but I would like something more that actually adresses the question of if the technology was advanced enough. Thank you, and sorry if I've come across as rude or forceful in my asking of this. —Preceding unsigned comment added by 213.114.115.208 (talk) 15:31, 25 May 2010 (UTC)[reply]
No, it took about 10 years from 1959 to develop technology to that level. See Apollo Program. -- Coneslayer (talk) 15:41, 25 May 2010 (UTC)[reply]
(edit conflict with Coneslayer) Almost certainly not. The first artificial satellite was only launched in 1957, and it wasn't until 1961 that anyone at all was put into space (and that was one person, for one short orbit, in a space capsule that was basically designed like a submarine; way too heavy to be suitable for a moon trip). In 1959, there just weren't rockets big enough, nor the technical knowhow to send someone to the moon and back. The first probe to the moon, Luna 1, did fly by the moon in 1959. However, the first three Luna missions, in 1958, all failed. The technology was coming along, but it was nowhere near ready to launch a person to the moon at that point in time. Buddy431 (talk) 15:45, 25 May 2010 (UTC)[reply]
Do you mean 1959 or is that a typo and you actually mean 1969? The moon landing in 1969 is considered fact and is the proof that the technology was advanced enough then to do it. I can't imagine what kind of proof could possibly be better than it actually being done. If you really mean 1959 then the rest of your question doesn't really fit, but the answers already given are correct. Both the USSR and the USA were doing everything they could to get to the moon as fast as possible, so I think we can safely assume that they couldn't have done so any sooner than they did. --Tango (talk) 15:54, 25 May 2010 (UTC)[reply]
But it wasn't - and that's remarkably trivial to prove to all but the most recalcitrant idiot. SteveBaker (talk) 19:33, 25 May 2010 (UTC)[reply]
To be fair, they probably could have done it a year or two earlier if it hadn't been for the Apollo 1 fire. That incident – and the subsequent capsule redesign – delayed the first manned Apollo launch by 21 months. TenOfAllTrades(talk) 16:05, 25 May 2010 (UTC)[reply]
True, but I don't think it delayed the first manned lunar landing by anywhere near that much. As I understand it, they turned some of the planned manned missions into unmanned ones, but still kept going along the same timetable. There may have been a delay, but I don't think it was as much as 21 months. I can't find the original timetable... --Tango (talk) 16:21, 25 May 2010 (UTC)[reply]
I can't rule out the possibility that if President Truman had announced in 1951 (as Kennedy did a decade later) that the U.S. would land a man on the moon and return him safely within 9 years, that it might have been feasible. It would have been a prestigious program, and better intercontinental ballistic missiles and spy satellites would have been valued spinoff. Microelectronics and computer technology would seem to be major hurdles to be overcome. Giving Von Braun and company the huge funding NASA received in the 1960s would have greatly accelerated building of the Saturn V. Edison (talk) 16:48, 25 May 2010 (UTC)[reply]
Perhaps, but it would have been a crazy thing for Truman to announce. We had V2 rockets in 1951, but that was it. There was no way he could have had any idea it would work. --Tango (talk) 17:25, 25 May 2010 (UTC)[reply]
Truman certainly would have had no idea it could be done, but Von Braun and the other rocket scientists were thinking about it. They just needed a big budget for R & D and they could have gotten to the moon years earlier than 1969. Edison (talk) 21:50, 25 May 2010 (UTC)[reply]
Sort of tangentially related, I like pictures such as this one taken of the Apollo sites recently from space. They don't do much to deter the conspiricy buffs (if NASA can fake a moon landing, surely they can fake a few photographs from their own spacecraft, the Lunar Reconnaissance Orbiter), but if you do accept the moon landings as fact, it provides an interesting link to the past. Buddy431 (talk) 17:17, 25 May 2010 (UTC)[reply]
There are mirrors left on the moon that are Corner reflector. With the right equipment you can shine a laser at moon and have it bounce back back. This proves at the least that there is man made equipment on the Moon. Anythingapplied (talk) 18:50, 25 May 2010 (UTC)[reply]
The thing is that the technology to get to the moon in 1969 would not have existed unless someone had decided years earlier to develop that technology. If someone had just woken up on Jan 1st 1969 and said "Hey! Let's go to the moon next month!" then of course that would have been impossible because they would not have had all of those years of prior technological build-up. Similarly, if Obama woke up today and said "Let's go to the moon on Jan 1st 2011" - then we couldn't do it...despite "having the technology". So if someone had decided that going to the moon would be an urgent priority in (say) 1939 - then maybe we would have had the technology to do so by 1959. These kinds of "What if history had been different?" stories are impossible to resolve. SteveBaker (talk) 19:33, 25 May 2010 (UTC)[reply]
Assuming the OP means 1969, they still do have I good point. It's really quite amazing what we were able to do with the technology, especially the limited computers (2048 words of RAM?!), of the 1960s. That's not to say that we didn't land on the Moon; we most certainly did. It just means that we should admire the technical proficiency and ingenuity of the engineers, scientists, flight planners, etc. who made it happen. Buddy431 (talk) 19:57, 25 May 2010 (UTC)[reply]
In the Shadow of the Moon is a great doco made a few years ago about the moon landings as told by the people who actually went there. I really enjoyed it. Vespine (talk) 22:30, 25 May 2010 (UTC)[reply]
Indeed. The most amazing thing to me is the fact that it occurred less than 70 years after the first heavier than air flight. I'm in awe of the fact that lots of people lived their lives where in childhood they knew only balloon flight and by retirement could see folks hopping around on the moon. It's a bit like going from a Fluyt to Alvin in two generations. Matt Deres (talk) 23:33, 25 May 2010 (UTC)[reply]
If I recall correctly, the "Journal of the British Interplanetary Society" published, in 1939, fairly detailed and reasonably accurate plans for a rocket to take humans to the moon. Sadly, what I read in the journal print edition many years ago does not appear to be available online. They specified things like the consumable oxygen and water needed, the mass of the ship, and the thrust from the engines, naturally without detailed blueprints of how the engines were built. That publication was noted by the United States Army Air Corps in 1942 [9], and by many other organizations. Scientific science fiction by such writers as Heinlein and Clark had astronauts navigating with star sights and using sliderules to make calculations, and sending back Morse code communications via shortwave. In addition, they had to actually fly the thing (as the Apollo 13 astronauts had to do on the emergency return trip), rather than having autopilot control or fly by wire. An earlier start of the "space program" and a disregard for loss of life comparable to, say early arctic expeditions, or efforts to climb Everest, might have allowed a moon landing a very long time before 1969. Edison (talk) 04:31, 26 May 2010 (UTC)[reply]
2048 words of dynamic state is a lot. I imagine that the computers were given that amount of RAM because that's how much they needed to do their job. I think that would still be true today, more or less, for the same reasons it was true then. You could move to a fancy memory-hungry operating environment, but it would be much harder to validate and I'm not sure you'd gain much in return. -- BenRG (talk) 05:23, 26 May 2010 (UTC)[reply]
Indeed - that's plenty. I built an entire telephone exchange control computer with only 1024 bytes of random-access memory back in the late 1970's - and I still fritz around making little 'fun' projects with Arduino computers which are capable of useful work with only 512 bytes of RAM (the chips only cost $5 - so they are great for making all sorts of fun projects)! The Apollo computer was mostly just a fancy calculator - and quite honestly, it wasn't required. If you watch the movie "The Right Stuff" (which isn't far from the truth) - you'll note that the NASA scientists didn't really want the astronauts to fly the spacecraft anyway - allowing the astronauts to do so was mostly a publicity stunt. Consider the Russian Lunokhod programme which was carried out at the exact same time as the NASA moon landings - with no computers anywhere in sight! Everything was done by remote radio-control from the ground, including soft-landing and deploying a rover, driving it around on the surface of the moon, returning photographs and TV footage, testing moon rock samples, deploying all sorts of scientific instruments, etc. Even the first Russian manned space stations had no on-board computers - they used paper tape sequencers (like a "player piano") to control complicated time-critical processes like re-entry manouvers. When the Apollo–Soyuz Test Project linked a US and Soviet spacecraft for the first time, it was remarked that the HP programmable calculators that the US astronauts carried in their flight suits were each vastly more capable than the entire Soyuz spacecraft. So computer technology was definitely not required on board the spacecraft in order to achieve the moon landings. Use of computers on the ground would have been more important - but we had commercial all-electronic calculators in 1961 - it's not much of a stretch to imagine a well-funded space program could push that development forward by a few years to make experimental computers sufficient for a 1959 moon launch. SteveBaker (talk) 14:06, 26 May 2010 (UTC)[reply]
Pendulum question
The following is a homework question, but I don't want a solution, just some clarification. (The problem is taken from Kleppner and Kolenkow, problem 8.3): "A pendulum is at rest with its bob pointed toward the center of the earth. The support of the pendulum starts to move horizontally with a unifor acceleration a, and the pendulum starts to swing. Find the angular acceleration α' of the pendulum. Find the period for which the bob continues to point toward the center of the earth."
I'm not sure what they mean by the angular acceleration of the pendulum. Do they mean at the very instant the support starts accelerating? In that case, I would imagine the answer would be a/L, where L is the length of the pendulum. But they don't mention L, so I assume this answer is incorrect. Also, is the bob is continuously pointing towards the center of the earth, then how is it swinging? Wouldn't the period be zero in that case? And then, wouldn't the length of the pendulum have to be the same as the radius of the earth? Please, any help would be appreciated. Thanks. 173.179.59.66 (talk) 18:18, 25 May 2010 (UTC)[reply]
I don't understand the question either. I guess it means the angular acceleration as a function of time since, if it is swinging, the angular acceleration won't be constant. If it it swinging, though, the bob can't be always pointing towards the centre of the Earth... I have tried to work out what would happen in the situation described, but I've failed so far. As I'm typing, I've thought of something I can try, so I'll get back to you. --Tango (talk) 19:19, 25 May 2010 (UTC)[reply]
No, I've failed. The problem I'm having is that we have a constant acceleration, rather than a constant force, and that acceleration is of the support, not the bob, so I just can't work out what to do with it. Given no information to the contrary, I'm treating the support as massless, which means the forces on it much balance, but I have no idea what either the external force is or what the tension in the string is. I need one of them to work out the other... If anyone else is better at mechanics that me and can work this out, I would love to know you did it! --Tango (talk) 19:30, 25 May 2010 (UTC)[reply]
Confusing question (is it a difficult book?) - it seems to me that at constant acceleration of the support the equilibrium position would be at tan(theta)=a/g where theta is the angle to the vertical - thus this is your equilibrium position. note : at this equilibrium position the bob/string does not point through the centre of the earth due to the acceleration
You should be able to calculate the force (sideways) on the bob at t=0 (?) and at positions offset from the equilibrium point. I'd assume the angular acceleration is wanted as a function (either of offset or of time) - the fact that it doesn't state which is confusing.
The swinging is caused by the bob becoming offset from the equilibrium position at the time the sideways acceleration starts acting (I assume it starts abruptly) ie at t=0 the pendulum is offset by angle theta given by the equation above.
If you are setting up the equations it seems easier to use a 'flat earth' with gravity pointing down rather than attempting to model a round earth..77.86.125.207 (talk) 19:30, 25 May 2010 (UTC)[reply]
the maths desk may also be able to help77.86.125.207 (talk) 19:33, 25 May 2010 (UTC)[reply]
I couldn't understand the question either until I looked it up in the book, where there is further text and a diagram that make the meaning clear. You are meant to approximate Earth as a sphere, not a plane. The horizontal acceleration is circular (around the center of the Earth). If α' (calculated at the moment the acceleration starts) is equal to the angular acceleration of the pendulum support about the center of the Earth, then the pendulum will continue to point toward the center of the Earth. Example 8.3 ("pendulum in an accelerating car") may be helpful. -- BenRG (talk) 20:06, 25 May 2010 (UTC)[reply]
First off, sorry if I gave the impression that I was assuming the earth was flat, my fault for not clarifying. But anyhow, I did something akin to what was described above, but I got some silly answers. If the pendulum is to continue pointing to the earth, then α'/L = a/Re, meaning that the pendulum should be the length of the radius of the earth. I used that to calculate what the pendulum's period would be were it not accelerating (2π*sqrt(Re/g)), but still this seems wrong, because I would think that the pendulum wouldn't be moving or swinging at all, if it's pointing continuously toward the center of the earth. 173.179.59.66 (talk) 21:38, 25 May 2010 (UTC)[reply]
According to User:BenRG below length of pendulum is the same as the radius of the earth - you were right. (bit of a trick question in my opinion).. 77.86.125.207 (talk) 01:19, 26 May 2010 (UTC)[reply]
I just can't arrive at a physical understanding of how this works. When the support starts accelerating (assume in the plus X direction), the pendulum bob will obviously lag behind. If the support accelerated to some speed then moved at constant speed, clearly the bob would swing forward and pass through the line between the support and the center of the Earth. But constant acceleration of the support would seem to leave the bob always lagging behind, by an increasing angle which would depend on the acceleration versus the gravitation, in a balance between the force (in the minus X direction) due to the acceleration of the support, and a force in the plus x direction due to gravity (with due acknowledgement of resolution of forces into components parallel to and perpendicular to the ideal massless thread connection the bob to the support). If the acceleration of the support were equal to gravity, why would the bob swing back and forth through the line connecting the support to the center of the Earth, rather than settling in at, say, a lagging 45 degree angle? Edison (talk) 21:44, 25 May 2010 (UTC)[reply]
reply to last question - 'hanging' at a 45 degree angle is right (for a=g) if it starts in that position .. this would also be the rest position of a damped pendulum.. but I would assume that the acceleration started abruptly (at t=0) and previously (t<0) the acceleration of the pivot was 0, thus as the new accelerating frame comes into being at t=0 the pendulum would be in a non-equilibrium position - hence the oscillations. (the line of the pendulum string would pass through the centre of the earth at the extremity of its oscillations in this case ie when Vbob,relative to pivot=0)
(of course in the question nowhere does it state that explicitly - but it's what I expect it to be implying - perhaps wrongly - I still confused about wording of question)77.86.125.207 (talk) 23:02, 25 May 2010 (UTC)[reply]
I assumed that when the acceleration started, it was previously 0 and instantaneously changed - this means that initial the line of the pendulum was passing through the center of the earth - thus (as above) - I get a shift in equilibrium position to a lagging the motion orientation.. Since initially the pendulum starts with the bob not in line with the 'lagging' equilibrium position it starts to swing.
I still don't really understand the second half of the question though .. when it says Find the period for which the bob continues to point toward the center of the earth. I assume this to be a time period - but it never continues to point towards the centre of the earth.. except under odd conditions - if time period of the oscillation is P then it instantaneously points towards the centre at t=0,P,2P,3P etc.. Also Find the angular acceleration α' of the pendulum - I assumed about the pivot, and not the earth.. this must be a function (except under curious circumstances) - either I'm totally misreading it, or the authors have a curious way of asking things.experience tells me it's the former yet I still think I'm right...77.86.125.207 (talk) 22:27, 25 May 2010 (UTC)[reply]
"Period" means "pendulum period", i.e. T = 2π/ω. The angular acceleration α' is about the pivot, and you're supposed to calculate it at the moment the pivot acceleration starts. I've solved the problem and I get the answer given in the book (T ≈ 1.5 hr). I'm not sure how much of a hint to give you. -- BenRG (talk) 00:49, 26 May 2010 (UTC)[reply]
(I'm not the OP) I've got to admit I'm totally stumped (same thought process as the OP so far) - though I finally understand what the question grammar meant . thanks. 77.86.125.207 (talk) 01:09, 26 May 2010 (UTC)[reply]
Doh. 1min later - reverse engineered your answer. OP's idea was right - pendulum must be length of earth radius. (I think both of us refused to accept that it might be anything like a trick question) Thanks.77.86.125.207 (talk) 01:19, 26 May 2010 (UTC)[reply]
There's something similar here about an 'accelerating frame of reference' [10] - linear not circular though, what it doesn't explain is the apparently strange questions that are being asked in the original question.77.86.125.207 (talk) 22:46, 25 May 2010 (UTC)[reply]
Thanks guys for the help-personally I think this was a bit of a stupid question, but that's just me... 173.179.59.66 (talk) 02:36, 26 May 2010 (UTC)[reply]
OK, I can understand that the bob would start pointing to the center of the Earth, then swing up to a lagging max, and if undamped, swing back to a point once more pointing tto the center of the Earth, but that is not the end of the story unless a flat Earth is posited. The support is travelling around a spherical Earth at constant acceleration. The rotation of the support around the center of the Earth will be negligible at the beginning of the experiment, unless the acceleration is very large, like many orders of magnitude greater than G. But after a while (depending on the unspecified acceleration) it is whipping around the Earth every few seconds, eventually approaching (but not equalling) the speed of light (hope the ideal string holding the bob is ideally strong). From the point of view of the "bob," the support is eventually twirling it around and around as it circuits the Earth, like a YoYo in the hands of a pro, hence it does point toward the center of the Earth relative to the support, due to the increasingly rapid whirling of the support around the Earth, just under once per rotation eventually, possibly overwhelming whatever the (unspecified) period of the pendulum was (maybe it was several minutes, or several hours). At 1 G acceleration how long until the support is racing around the Earth once per second? How soon would it approach c? Edison (talk) 04:11, 26 May 2010 (UTC)[reply]
If memory serves, 1g acceleration gets you to c in about a year (ignore relativistic effects, of course). (Google's calculator confirms this approximation.) Of course, that is linear acceleration - the support in this case is accelerating due to gravity (and being held down, presumably, once it gets above orbital speed) as well, but that is perpendicular to motion so can be ignored. --Tango (talk) 11:21, 26 May 2010 (UTC)[reply]
The gravitational attraction on the bob if it is not between the support and the center of the Earth will resolve into a component in line with the thread (which has no effect) and a component at a right angle to the thread, which will certainly cause the bob to move, along with the force due to the acceleration of the support along the Earth's surface, which will also resolve into components normal to and orthogonal to the thread. Plus as noted the support is moving along a circle of radius about 4000 miles, which might be a negligible effect (or not, since this is physics and not engineering, and the acceleration and period were unspecified) . Edison (talk) 12:59, 26 May 2010 (UTC)[reply]
I was thinking of the bob with the period that means it always points towards the centre of the Earth. --Tango (talk) 17:01, 26 May 2010 (UTC)[reply]
perkinson's disease
Explain how you would an Augumentative and Alternative Communication device with one suffering from perkinson's disease to enable effective communication —Preceding unsigned comment added by 41.204.168.3 (talk) 18:26, 25 May 2010 (UTC)[reply]
This looks like a homework question, and we aren't supposed to do those for people. Regards, Looie496 (talk) 18:38, 25 May 2010 (UTC)[reply]
We also have an article on Parkinson's disease, which could prove helpful for links to other websites. Brammers (talk) 19:31, 25 May 2010 (UTC)[reply]
How to tell if plastic is degradable
I was reading through my science book on the last day of school (I know, how unusual for a young person to actually read a textbook when not required to by a teacher), and I saw something about a plastic fork formulated to biodegrade in a week if burried. That got me wondering if the plastic silverware at the hospital or school cafeterias could possibly be degradable plastic. Is there any to tell other than the recycle codes, which isn't present? The ones at the hospital are made by Sysco and if they're not bioplastic (which I wouldn't know because I'm not overly familiar with that type), then they seem to be polystyrene, which I do not believe is biodegradable. The ones at school are more like polyethelene or polypropyline, if not some sort of bioplastic. PCHS-NJROTC(Messages) 19:57, 25 May 2010 (UTC)[reply]
Probably they aren't biodegradable, but you can just do an experiment to see. Bury them in dirt and forget it for a year. Dig it up and see if it is decomposed. I an a student and I read my science book through and through whether teacher says to or not. Also plasticsilverware? --Chemicalinterest (talk) 20:04, 25 May 2010 (UTC)[reply]
The only biodegradeable plastic I'm aware of in common use is Polylactic acid - there are ways to tell if it is this - notably it cannot hold a hot liquid (put in boiling water), it is also chiral which you might possibly be able to tell (if it's transparent -easier for a cup) - otherwise bury it and see (or ask).77.86.125.207 (talk) 20:16, 25 May 2010 (UTC)[reply]
e/c ::Good to see I'm not the only one that went to school to learn and not just to get a piece of paper. So what are the general characteristics of bioplastics, and what are their most common uses? I see that plastic bags appear to be a big one, and although bags I see almost always have a 2 or 4 resin code for polyethelene, I've see some of such that say degradable. I'm assuming that would be Bio-derived polyethylene. I sometimes see food containers that have 7 resin codes (7 other), so I'm assuming that could be PLA or some other sort of bioplastic? Are bioplastics usually labeled as such with pride, or are they often "undercover?" PCHS-NJROTC(Messages) 20:27, 25 May 2010 (UTC)[reply]
Resin code 7 includes Polycarbonate which is/was used for bottles, could also be Styrene-acrylonitrile resin for containers (plastic cups), polylactic acid (disposable plastic cups), or many other things.77.86.125.207 (talk) 20:40, 25 May 2010 (UTC)[reply]
They contain bad chemicals, though. 67.243.7.245 (talk) 22:06, 27 May 2010 (UTC)[reply]
I don't know whether ChemicalInterest's aside was intended as a joke or not, but I've noticed that at least some Americans say "silverware" where I would say "cutlery". Then of course there are plastic glasses ... --ColinFine (talk) 21:37, 28 May 2010 (UTC)[reply]
reducing MAC layer handoff latency
i was studying the different ways to reduce handoff latency in wlans (ieee802.1x) when i found this[11] (page18:tableII) comparison among the many popular techniques adopted. in it there is a criteria called signalling overhead. what does this "SIGNALING OVERHEAD" mean? i have given many searches regarding the topic but havn't found anything concrete. i would be very thankful if anybody can shed some light on the matter. --scoobydoo (talk) 20:18, 25 May 2010 (UTC)[reply]
The "signalling overhead" is the amount of the tranmission that is not data, but is other information required to ensure that the data arrives correctly at the right place and time.
ie consider a written letter to a friend, the 'signalling overhead' in this case would be the address written on the envolope.
More specifically it's the amount of bandwidth wasted/bandwidth disrupted, rather than the absolute data amount
You might get a better answer on the computing desk.77.86.125.207 (talk) 20:30, 25 May 2010 (UTC)[reply]
In this specific case, it's talking about all the network traffic that the different strategies discussed use. In order to be able to perform a (hopefully seamless) transition from one access-point to another, the different strategies preemptively start new (concurrent) connections to potential APs, so that if the current connection dies we're already some or all of the way through establishing a fresh connection to a better AP (so our phone call or video stream or whatever can continue unmolested). The more aggressive strategies actually establish and authenticate connections, so they're ready to go. But doing this involves extra communications to one or several nodes, using bandwidth (and placing extra stress on potentially busy nodes). This extra traffic (which mostly results in establishing connections that go unused) is wasted - it's the overhead. Less aggressive strategies impose less overhead (they don't try so hard), but are at greater risk of a material interruption if things go wrong. -- Finlay McWalter • Talk 20:46, 25 May 2010 (UTC)[reply]
yes, i've got it now. that's why channel masking techniques got such low overhead signaling stats seeing as that it hardly mantains much contact with other APs.... thanks a lot. --scoobydoo (talk) 14:35, 26 May 2010 (UTC)[reply]
Cats - gender and coat colour
This is the grandmother of the kitten. This is the colour I'm talking about.
I know that a tortoiseshell cat is very likely female, because the coats of (normal) male cats can't be black and orange at the same time. Well, a tortoiseshell cat I take care of gave birth to five kittens. One of them is grey (like the Russian Blue) with a yellow stripe on its head. Is it likely that the kitten is female? Do the genes that produce grey (blue) and orange coat act like the genes that produce black and orange coat? Surtsicna (talk) 21:17, 25 May 2010 (UTC)[reply]
Yes, but I don't understand a word of it. Actually, I have understood that tortoiseshell cats can only be females but I haven't found the answer to my question.
For a cat to be tortoiseshell, calico, or one of the variants such as blue-cream or chocolate tortoiseshell, the cat must simultaneously express two alleles, O and o, which are located on the X chromosome. Males normally cannot do this, as they have only one X chromosome, and therefore only one allele, and so calico cats are normally only female. I am not sure that "blue-cream" is the colour I'm talking about. Is the cat on the photograph a "blue-cream" cat? Surtsicna (talk) 22:12, 25 May 2010 (UTC)[reply]
Can I suggest, as a practical matter, that there are easier and more reliable ways to determine the sex of your kittens? I'm aware that Googling "sex kittens" will get you quite a lot of, err, "noise", but here's a practical article (warning, pictures of kitten butts... should be safe for work, I guess, unless they prohibit kitty porn, hyuk hyuk hurrrr). --Mr.98 (talk) 01:37, 26 May 2010 (UTC)[reply]
I have book on cats wich has a list of possible coat colors depending on parents, tortoiseshell cats are capale of producing blac, blue, red, cream and red-cream males, which suggests that if your kitte indeed is blue-cream it`s a female, I`m not sure though that one stripe constitutes fur color - that may come from some diffrent gene, for example, I had a cat who had a white stripe on neck as did all her black and blue kittens regardless of gender. Speaking of which the method suggested by person before me is more efficient - take kitten by neck skin so that it curls up, draw back tail, look at its butt - both sexes have two... um... openings, the diffrence is that in females they are very close to each other and of equal size, while in males, they are further apart, lower hole is slightly smaller, plus their sexual organs form a small bump. In my expierience if you have five kittens they are not of one sex - compere and you`ll figure it out ~~Xil (talk) 09:50, 26 May 2010 (UTC)[reply]
Thanks for answering! I am aware that checking below the tail is easier than guessing on the basis of colour but I really don't want to touch the kittens. They are only four days old and they are their mother's first litter. I don't want to upset her, as I'm afraid she might abandon them. In the last litter of 5 I had, all 5 were females (including 2 tabbies, a black-white-orange one, a blue-white-orange one, and a tortoiseshell - the new mother) Surtsicna (talk) 21:30, 26 May 2010 (UTC)[reply]
I sugest looking at the cts genitals and then you can, hopefully, tell us what sex it is, if not you have bigger things to worry about than this —Preceding unsigned comment added by 62.172.59.90 (talk) 09:06, 26 May 2010 (UTC)[reply]
That was needlessly rude - and incorrect. Sexing of young kittens is not necessarily straightforward. When we got our kitten, for example, both vets in the clinic said they thought it was male, but said that it wouldn't become clear until the kitten had gotten a bit older. The kitten in question (which was indeed male) was probably only 8 weeks old at the time. And the next time you decide to impugn someone's intelligence, make sure you know how to spell words like "cat" correctly. Matt Deres (talk) 13:42, 26 May 2010 (UTC)[reply]
Thank you for your reply, Matt Deres! Surtsicna (talk) 21:30, 26 May 2010 (UTC)[reply]
May 26
What's wrong in this picture?
According to the description of this image, the photographer had a cellulitis infection on his knee. How would he know that the knee is infected, since the only discolouration is at or below the middle of the photo, and the knee is above the top of the photo? Nyttend (talk) 02:28, 26 May 2010 (UTC)[reply]
Best guess: he meant to say "shin". --Jayron32 02:37, 26 May 2010 (UTC)[reply]
Better idea: Ask him. He doesn't appear to be active at Wikipedia any more, but you could always try the "email this user" function. --Jayron32 02:43, 26 May 2010 (UTC)[reply]
Nyttend didn't upload the image. He asked the question... Duh... --Jayron32 04:54, 26 May 2010 (UTC)[reply]
The actual contributor of the photograph was User:RafaelLopez - and he hasn't edited Wikipedia since 2007. However, there is an email link on his user page (although it may no longer work after so much time has passed). So I suppose you could try emailing him to ask. SteveBaker (talk) 13:41, 26 May 2010 (UTC)[reply]
I'm not that interested; it was simply curiosity, since all I could see was the discolouration in the lower part of the picture. I'm somewhat colourblind, so I was wondering if perhaps there was something above the dark splotch that my eyes couldn't see. Nyttend (talk) 01:29, 27 May 2010 (UTC)[reply]
types of life
With the recent news about "synthetic life" I've read a couple of articles talking about the "definition of life" and how it is probably not worth arguing, but I felt that it might be useful to at least define certain limits to the description of life and non-life by attaching names to features of natural systems. I've just quickly put together a few names, if they seem off, awkward, contrary, unjustified, or irrelevant in any way let me know! I've used the suffix -ate rather arbitrarily. The point here is that each category should be necessary for the following category, so for example 2 shouldn't be possible without 1, and 3 shouldn't be possible without 2. If there are exceptions, then I'll have to scratch these and think some more lol.
1) syntropate (or negentropate) from "syntropathy", basically any natural system that mantains or lowers entropy. I don't know if anything exists exclusively in this category, but I think it's possible. maybe crystals could be considered syntropate?
2) holoplicate (holo "whole" plico "copy"), or a holoplicatic syntropate, would be a sytropate that has the ability to replicate, though no mutation is possible, either because replication is perfect (which as far as I know isn't possible), or because any flaw results in complete failure of the system (which may be the case for man-made artificial life, i.e. replicating robots, though I'm a bit unsure about this)
3) ateloplicate (atelio "imperfect"), or a ateloplicatic syntropate, would be a syntropate that replicates introducing flaws in its copy. all commonly recognizable life would be included in this group.
I was thinking of another group that would include systems capable of accessing it's own code and modifying it on the fly, but I'm not sure if that warrants a category because it could include some microbes as well as humans, and it might be exclusive of (3).
You're free to do whatever you want in your own head. Getting another person to use your system would require you to get published in a peer-reviewed journal or something like that... --Jayron32 03:04, 26 May 2010 (UTC)[reply]
Well of course, I'm just curious if a categorization such as this has any relevance towards describing the types of life/non-life that might exist in the universe! 210.165.30.169 (talk) 03:09, 26 May 2010 (UTC)[reply]
I'm fairly certain that maintenence of entropy is a common theme in attempts to define life eg eg I've seen the idea many(?) times. As far as I know the old fashioned definitions are still used. (I assume you've seen the disclaimer on Wikipedia:Reference desk/Science at the top "does not ..opinions ..debate" etc ..77.86.125.207 (talk) 03:49, 26 May 2010 (UTC)[reply]
Hmm... you're right. I'm pretty sure that rule wasn't there when I last revised the header some 6 years ago, but it's not really my place to argue. Sorry, I'll retract my question? comments? then. 210.165.30.169 (talk) 04:03, 26 May 2010 (UTC)[reply]
As far as I know nothing apart from life is capable of maintaining it's own entropy (definately not crystals) .. are further definitions really needed. Just use No.1 that's my suggestion - perhaps there is an exception.77.86.125.207 (talk) 03:55, 26 May 2010 (UTC)[reply]
I think a photocell coupled to a battery and put outside in the sunlight would be an exception Androstachys (talk) 12:52, 27 May 2010 (UTC)[reply]
What animals can use the widest range of useful light strengths?
Some animals are mostly nocturnal. Some have vision that is mostly useful in the day time. Some animals, such as cats, have vision useful both in the day, and in low nighttime light levels. Which animals have the greatest useful visual range? —Preceding unsigned comment added by 24.130.145.253 (talk) 04:13, 26 May 2010 (UTC)[reply]
Any animal which has cone vision and goes out in bright daylight can use daytime illumination,(adapting by contraction of the iris in addition to retinal adaptation) so the medal must go to one of the animals which also had nocturnal vision via rods, a large pupil, and a reflective Tapetum lucidum to maximize night vision (though there is a decrease in acuity in bright light). It would be an animal specialized for nocturnal life which can function in full daylight (one not "blinded by the light" as the Mole (animal) and Bat are sometimes claimed to be). Zoos have some scary looking animals specialized for nightlife, with really big eyes. Owls would be in the running. Huge eyed mammals like the Bushbaby, the Aye-aye and other Lemurs seems like another candidate if it can function in daylight. They lose points for having no fovea, thus poor visual acuity in daylight. Primates seem to do better in daylight with a good fovea "The topography of primate retina: a study of the human, bushbaby, and new- and old-world monkeys.". Cats, dogs and raccoons have good night vision, with the reflective tapetum, and also see pretty well in daylight. Edison (talk) 04:50, 26 May 2010 (UTC)[reply]
Cuddlyable3 with Welding goggles and a night vision device or a large optical telescope would definitely exceed the useful light range of any lemur or owl not so equipped, so it looks like humans win. Edison (talk) 22:06, 26 May 2010 (UTC)[reply]
We do however have Welding helmet. Perhaps a merge/redirect is in order (or maybe the items are sufficiently different to warrant separate articles). Buddy431 (talk) 03:28, 27 May 2010 (UTC)[reply]
Uses of Stars
What are uses of stars?ugygdyowerg —Preceding unsigned comment added by 76.174.168.105 (talk) 05:04, 26 May 2010 (UTC)[reply]
There's one star we use a LOT, see Sun. Otherwise, people have used the stars to make constellations, i.e. draw pictures in the sky and tell stories about them. Stars have been used as navigation aids (see Celestial navigation). Hope that gets you started on some ideas. --Jayron32 05:28, 26 May 2010 (UTC)[reply]
I believe that stars still are used as navigation aids by many indigenous people. Many people attempt to use them to predict the future, compatibility between people and all sorts of things. -- Q Chris (talk) 09:00, 26 May 2010 (UTC)[reply]
Stars are not used to predict the future. You are probably thinking of astrology, which uses the planets.--Shantavira|feed me 15:39, 26 May 2010 (UTC)[reply]
Stars are also used to derive the calendar and to know how long a year is, and to determine where the earth is in space. Stars are also used for navigation by space ships. They have also led to some discoveries such as helium and nuclear fusion. Graeme Bartlett (talk) 10:35, 26 May 2010 (UTC)[reply]
I'm not really sure what an "indigenous person" is, but I suppose I might count - I certainly use the stars for navigation. --Tango (talk) 11:27, 26 May 2010 (UTC)[reply]
Stars provide some light at night - especially the milky way.[citation needed]Ariel. (talk) 11:31, 26 May 2010 (UTC)[reply]
Stars consume light elements like hydrogen and helium and use a fusion reaction to make heavier elements like oxygen, carbon, iron, uranium, etc. When a star 'dies', the result is often the explosive release of these heavy elements out into the surrounding regions of space. At the start of the universe (at the big bang) there were only light elements, it's safe to say that without stars, there would be no nice rocky planets, no atmosphere, no water, no animals, plants or people. Without stars, the universe would be nothing more than a big fuzzy ball of hydrogen gas. SteveBaker (talk) 13:35, 26 May 2010 (UTC)[reply]
Stars are a very useful way of motivating children at school, red ones are the best. They are given (awarded sounds better) for good work or behaviour. They are also used in WP to help people feel recognised - and why not I say. Caesar's Daddy (talk) 13:48, 26 May 2010 (UTC)[reply]
The best stars are self-contained fusion reactors that produce amazing amounts of energy, even enough to provide light and heat 100 million miles away. 65.121.141.34 (talk) 16:15, 26 May 2010 (UTC)[reply]
Some stars entertain us and provide material for gossip columnists. Edison (talk) 22:01, 26 May 2010 (UTC)[reply]
Residual stresses in the coatings given on insetrs
What are the methods avialable to find the residual streses present in the coatings given on carbide inserts? —Preceding unsigned comment added by 122.248.132.54 (talk) 07:44, 26 May 2010 (UTC)[reply]
Xray diffraction is one method ie search "x ray diffraction surface stress" or similar.77.86.125.207 (talk) 16:55, 26 May 2010 (UTC)[reply]
Is blood group a factor in organ transplantation ?
I was just waching an episode of CSI:NY in wich they speculate that crime was comited to harvest victims liver ecause she had AB+ lood type which is very rare. To my knowledge the idea of AB blood type being rare is quite popular misconception (as people with that type of blood can receive blood of all other types). So I am wondering if lood type can acctualy play any role in organ transplantation ? (I figure there wouldn`t be much blood left in the organ...)--~~Xil (talk) 08:55, 26 May 2010 (UTC)[reply]
Here's a compatibility chart. Seems like CSI got it quite wrong. AB is not a type in high demand as a donor - AB can only give to AB, but AB can get from anyone. BTW to avoid Graft vs host disease the compatibility chart is reversed - but that's for bone marrow, not livers. Ariel. (talk) 11:12, 26 May 2010 (UTC)[reply]
buying lemon juice
this site says "lemon juice an inexpensive, readily available acid for use in educational science experiments." but my store sells only tiny bottles 6 oz of it. its expensive too. im looking to buy it by the liter or gallon. iv looked online and cant find it either. it needs to be food grade. and not have any other chemicals or preservatives in it. —Preceding unsigned comment added by Tom12350 (talk • contribs) 09:00, 26 May 2010 (UTC)[reply]
It isn't that inexpensive, lemons are expensive too. Go with acetic acid (vinegar) or hydrochloric (muriatic) acid or even possibly food-grade phosphoric acid.
it needs to be liquid so citric acid powder is out. iv tried vinegar ect i Need lemon juice for my application. iv bought the frozen Minute Maid lemon juice but it only comes in tiny bottles. i need it by the liter or gallon.
You might want to be a bit more specific about what type of experiment or demonstration you're conducting. (Incidentally, citric acid dissolves very readily in water; it's the acid that gives lemon juice its bite.) TenOfAllTrades(talk) 11:45, 26 May 2010 (UTC)[reply]
I agree - you shouldn't dismiss citric acid. Dissolve the stuff in water first - now you have a liquid containing citric acid - which is what you really wanted the lemon juice to be. It has three major advantages over lemon juice: (1) It doesn't contain all the other junk (sugar, pulp, etc) that lemon juice has that could mess up your results (2) It's much cheaper (3) You have good control over the concentration. Since "food grade" citric acid is the "active ingredient" in lemon juice, it's just as safe for the kids. IMHO, it's better to tell them it's "citric acid" and that they are under no circumstances to eat it/taste it/whatever than to give them the impression that it's safe to do that with random chemicals in a science experiment! In other words - you can be 100% safe if they do screw up and start drinking the experiment - but still give the impression that this is a "proper" science experiment and start to instill the kinds of discipline they'll need when they move on to experiments with more dangerous chemicals. When the experiment is done, you can explain that citric acid is a major ingredient of lemon juice and that they could subsitute lemon juice if they wanted to repeat the experiment at home. SteveBaker (talk) 13:20, 26 May 2010 (UTC)[reply]
i dont want to have to dissolve it i just want to buy it in liquid form. i need it for degreasing items and for cleaning food surfaces as well as to drink (i like to drink lots of lemon aid as well) —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:32, 26 May 2010 (UTC)[reply]
Try washing up liquid - it is specially designed for cleaning grease and will do a better job than lemon juice. --Tango (talk) 14:15, 26 May 2010 (UTC)[reply]
iv already tried it. lemon juice works well for what im doing. thats what i want to use. —Preceding unsigned comment added by Tom12350 (talk • contribs) 15:12, 26 May 2010 (UTC)[reply]
My grocery store has lemon juice in 24oz bottles in the juice aisle, so it is available in some places anyway. 65.121.141.34 (talk) 16:12, 26 May 2010 (UTC)[reply]
It seems like vinegar would be much more convenient to use in bulk for educational science experiments, and the pH for concentrated vinegar is hardly different from the pH of lemon juice. Looie496 (talk) 21:58, 26 May 2010 (UTC)[reply]
Why buy it in liquid form?!? That's just silliness. When you have lemon juice, you are buying (essentially) a mixture of citric acid and water. If you buy pure citric acid, you can just add your water and make ersatz lemon juice. The cost difference per gram between lemon juice and the powdered citric acid is simply the cost of water. Why pay extra cash for something you get almost for free out of your faucet?!? --Jayron32 00:46, 27 May 2010 (UTC)[reply]
Plus, even concentrated lemon juice contains significant amounts of sugar, which makes it a lousy cleaning agent. If you really want an acid to clean stuff, just buy white distilled vinegar. Its one of the cheapest, best cleaning agents out there. --Jayron32 00:50, 27 May 2010 (UTC)[reply]
how stationary is geostationary?
If someone were hanging just above the ground from a cable depending from a geostationary satellite, how much would they be moving around? Would they be swinging? bobbing up and down? racing to and fro? or would they be more or less still?
The satellites in these orbits move around in a figure 8 shape. The satellite operator will try to contain this inside a specified cube, while minimising fuel use. Allow for a tenth of a light millisecond (30 km) up and down each day, and with east west and north south added in. The angle should stay withing about 0.1 degree unless it is abandoned and goes into an inclined orbit. Graeme Bartlett (talk) 10:29, 26 May 2010 (UTC)[reply]
It's a bit more complicated than that. The weight of the person will change the orbit of the satellite. In order to compensate you will need to raise the orbit, but then it won't be geosynchronous. More accurately the center of mass of the satellite/person combo will (could) be in geosynchronous orbit - BUT - if the cable was rigid everything would be fine, but with a flexible cable the orbits of the person and the satellite won't match. Ariel. (talk) 11:00, 26 May 2010 (UTC)[reply]
Anothing thing -- a person "hanging just above the ground" would be subject to the wind. The person and cable would swing freely like a pendulum on a string, its period depending on the mass of the cable (some of which is high enough that gravity is appreciably weaker) compared to the mass of the person, but a rather long period in any case. Each change of wind would change the motion, and this effect would combine with the orbital effects already described. Also to be considered is that the cable would certainly have some elasticity, so anything generating a vertical motion would tend to initiate a slow bouncing action. --Anonymous, 20:45 UTC, May 26, 2010.
Sagrada Familia (Barcelona)
Two triangles marked 19-1-07 and a crack in Sagrada Familia inner wall. Help needed: What is the purpose of the two triangles? Thanks! Etan J. Tal 10:19, 26 May 2010 (UTC) —Preceding unsigned comment added by Etan J. Tal (talk • contribs)
It's some sort of telltale designed to enable someone to evaluate the extent to which the crack is developing, and or the relative directions of travel of the two plates as they move relative to eachother. --Tagishsimon(talk) 10:40, 26 May 2010 (UTC)[reply]
Similar to this I think: Ariel. (talk) 11:04, 26 May 2010 (UTC)[reply]
Given that the line between the two triangles isn't straight, it might be a tie to hold the crack together, that has snapped under the strain. Otherwise, I'd go with Tagiahsimon. CS Miller (talk) 12:59, 26 May 2010 (UTC)[reply]
I agree - it's obviously a tell-tale to let someone monitor how bad the crack is - whether it's growing or slipping, etc. Hence the reason for putting a date on it. Personally - when my house was new and started to develop a crack, I just drew a line across the initial hair-line crack with a pencil and dated it (fortunately mine was just a 'stuff drying out and settling after construction' kind of a crack and all was well). That's enough to let you know how much it grew in how much time - and (critically) whether there is any lateral slippage that might indicate a dangerous situation. SteveBaker (talk) 13:24, 26 May 2010 (UTC)[reply]
I thought it has to do with some earthquake, but couldn't find any on that day. It seems you are right - thanks to all of you! Etan J. Tal 20:36, 26 May 2010 (UTC) —Preceding unsigned comment added by Etan J. Tal (talk • contribs)
It is common in old historic buildings to monitor cracks by cementing a piece of glass or ceramic across the crack. If the crack is widening or narrowing, or the two pieces are moving relative to one another, the little brittle piece will tell the story. It would have little chance of preventing the crack from widening. Edison (talk) 21:57, 26 May 2010 (UTC)[reply]
four classes of consumables
(NOTE: This question is NOT about "calories.") Years ago I read the basic formula, Fat: 1 gram = 9 calories. Protein: 1 gram = 4 calories. Carbohydrates: 1 gram = 4 calories. Alcohol: 1 gram = 7 calories. (Again: This question is not about calories or about the preceding formula.) What's always seemed strange to me (ignorantly) is the aspect of "one of these things is not like the other": i.e., that "alcohol" seems somehow not to fit in this apparently comprehensive list. SO, Q: Is this list comprehensive, and if so, in what category? Are there other things with "calories" but which aren't digestible and so are not included? Also, three of the four are necessary, in the long run, for nutrition; is alcohol in any way necessary? Does everything we consume fit into one of the four categories (excluding bizarre things, like eating chalk or clay or whatever). And so on, on the basic theme of this list of four and only four classes of consumables. 63.17.33.231 (talk) 11:11, 26 May 2010 (UTC)[reply]
The list is most definitely not complete. For example there are sugar alcohols with a wide range of calories (see the article). Carbohydrates don't all have the same calories per gram (some have less). And there are also organic acids. See Food energy for a chart. And BTW carbohydrates are not necessary, protein and fat is enough. Ariel. (talk) 11:22, 26 May 2010 (UTC)[reply]
Thanks, Ariel. So there's fat, carbs, protein, alcohol (I presume sugar alcohol is alcohol), and organic acids. Anything else? And what "category" does this list compose? 63.17.33.231 (talk) 11:58, 26 May 2010 (UTC)[reply]
Sugar alcohol is not alcohol (ethanol). And like I said, see Food energy for the list. There are probably other things too, but none that are commonly eaten. I don't think the list could ever be considered complete. The food energy article calls these things Cellular respiration, so I guess that's your category - it's a list of things that can be oxidized by the body. It also mentions how bacteria can use metals - I wonder if humans can use them in tiny amounts. The reason this list can never be complete is that lots of things can be oxidized. For example humans can oxidize acetone (and ketones in general, are used by the brain, but I don't think are eaten directly, and are not on the list). Ariel. (talk) 12:02, 26 May 2010 (UTC)[reply]
The term macronutrient is usually applied to the collection of fats, proteins, and carbohydrates. But not alcohol. 198.161.238.18 (talk) 15:37, 26 May 2010 (UTC)[reply]
That is just a condensed list for ease of calculation of the number of calories in a food when they find out how many carbohydrate grams, fat grams, etc. are in the food. --Chemicalinterest (talk) 19:32, 26 May 2010 (UTC)[reply]
At first I thought "you might not want acetone on a list of foods" until I read about it's apparently low toxicity. Learn something new every day, huh? Kind of like how glycol will kill you, and glycerol will (safely) sweeten your food. --Jmeden2000 (talk) 20:52, 26 May 2010 (UTC)[reply]
A neutral body is one that has no netcharge. Whether that qualifies as being "chargeless" may depend on the textbook you use for definitions. — Lomn 13:00, 26 May 2010 (UTC)[reply]
To clarify, it's possible for a molecule to possess segments which are charged but that overall, produce no net charge. An example could be an amino acid, which possesses both an amine group and a carboxylic acid. While they may technically not exist as charged terminal portions at the same time, theoretically, you can understand, and perhaps someone else with more chem knowledge could provide a real-lie example. DRosenbach(Talk | Contribs) 15:31, 26 May 2010 (UTC)[reply]
Or even like a hand-full of of table salt...50/50 mixture of Na+ and Cl– so every atom is charged and but is overall (net charge, sum of all the pieces) neutral. DMacks (talk) 17:58, 26 May 2010 (UTC)[reply]
Or the atoms themselves, the nucleus is positively charged; the electron cloud is negative. CS Miller (talk) 18:07, 26 May 2010 (UTC)[reply]
And while we're there, those neutrons are composed of (balanced/net-neutral) charged quarks. DMacks (talk) 18:21, 26 May 2010 (UTC)[reply]
What is the definition you are using for "neutral body?" That would help in formulating an answer. Edison (talk) 02:37, 27 May 2010 (UTC)[reply]
Astronomical query
Το μικρότερο γνωστό αντικείμενο της Ζώνης του Κάιπερ.
It's quite possible that it hasn't been named - it's a pretty boring lump of rock amongst billions of other boring lumps of rock - so it doesn't really need a name. It's also possible that some boring astronomical naming panel has to meet to agree on a name. If you are desperate to know - then at the bottom of this article are the email addresses of two of the scientists involved in the search. You could ask them. Incidentally - the article I linked to is really fascinating. Aside from it's size, the most interesting thing about the object in question is how it was discovered. It's 100 times dimmer than the dimmest thing the Hubble's best imaging system can see! They actually used some rather interesting techniques using the telescopes guide-scope to discover the rock as it occluded light from a distant star that the Hubble happened to be using to stabilize itself! (Incidentally - the picture our OP linked to is an artist's impression - which for a rock whose only known properties are roughly where it is and approximately how big it is - is something of a stretch!) SteveBaker (talk) 13:05, 26 May 2010 (UTC)[reply]
It is strange that neither that article or the description of the picture on the NASA site give the designation of the object. It may well not have been named, but it should automatically get an alphanumeric designation (see Provisional designation in astronomy). --Tango (talk) 14:02, 26 May 2010 (UTC)[reply]
Yeah, I'm pretty unhappy about that artist's depiction — for me, being fanciful about what it may look like is fine, but I dislike physical impossibilities: What is lighting that thing up?? Comet Tuttle (talk) 17:29, 26 May 2010 (UTC)[reply]
Another spaceship off to the right somewhere, with a huge spotlight, isn't it obvious? The Sun is just visible at the top-left of the object. CS Miller (talk) 18:05, 26 May 2010 (UTC) [reply]
sticker
what type of glue is on stickers such as childrens stickers or stickers found on food products. —Preceding unsigned comment added by Tom12350 (talk • contribs) 15:18, 26 May 2010 (UTC)[reply]
Any data on how often something happens during a living organ transplant (kidney, liver) and the donor dies during or shortly after the operation? —Preceding unsigned comment added by 20.137.18.50 (talk) 17:14, 26 May 2010 (UTC)[reply]
Soccer matches often played under heavy rain
Wouldn't this increase the chances of pneumonia etc.? I thinkn a U.S. president died after making a speech in rain. 67.243.7.245 (talk) 18:39, 26 May 2010 (UTC)[reply]
That would be William Henry Harrison. He died one month after giving his inaugural address; two hours in the pouring rain on a cold March day. CS Miller (talk) 18:47, 26 May 2010 (UTC)[reply]
(ec) Not really. The connection between cold weather and illness is mainly due to people spending lots of time indoors in close proximity to other people. A US president may well have died after making a speech in the rain, but I doubt he died because he made a speech in the rain. (If you actually get hypothermia, then that is bad, but you certainly won't get that running around on a football field (they wear hats and gloves in cold weather) and it would be hard to get it giving a speech.) --Tango (talk) 18:49, 26 May 2010 (UTC)[reply]
He probably died because of the cold, but the cold weather just augmented the virus. If you aren't sick, you shouldn't have any trouble being out in the cold. --Chemicalinterest (talk) 19:30, 26 May 2010 (UTC)[reply]
He didn't develop his illness until several weeks after his inauguration, so it's likely that it had very little to do with his death. Buddy431 (talk) 21:32, 26 May 2010 (UTC)[reply]
There's also zero evidence that cold weather, in and of itself, either causes OR exacerbates upper respiratory infections (cold, flu) one gets during the winter seasons. When controlled studies have been done, there has been no connection found between being cold and wet and getting sick. --Jayron32 00:41, 27 May 2010 (UTC)[reply]
Cold temperatures may weaken the immune system as blood flow may be restricted to the head area. If an infection or viruses are already present, then the infection may be affected in the time that the blood flow and white blood cells are reduced. ~AH1(TCU) 01:44, 27 May 2010 (UTC)[reply]
Yes, that would be a plausible mechanism to explain a connection, were any such connection observed. Jayron's point is that, under controlled conditions, no such connection is observed. --Trovatore (talk) 01:51, 27 May 2010 (UTC)[reply]
The only time I've played football (or soccer as some call it) was when I was a schoolboy. Then, whenever it rained we would all stop and seek shelter. Why would anyone want to play football in the rain? 92.15.6.183 (talk) 21:38, 26 May 2010 (UTC)[reply]
Because the cost of cancelling a professional football match is enormous. --Tango (talk) 22:55, 26 May 2010 (UTC)[reply]
(after ec)In Britian football/soccer gets played in any weather, provided that it's not so rainy that the ball is brought to a halt by waterlogged ground if you pass it low, or the pitch is frozen solid, or there's so much snow on there that it can't be cleared/flattened enough to approximate a level surface by 3pm. Just the way it is - and has always been ever since the game started. In the amateur leagues, they don't even seem to care much about that. There are some stadiums that are notorious (thinking Blackpool and Oldham in particular) for gusts of wind so strong at times that if hoofing the ball into the wind, it can actually end up behind the kicker - and they still play. It's an oft-repeated comment about South American/Southern European/African footballers (who have a reputation for being mad-skilful but 'sensitive' and 'fussy', whether it's true or not) that 'Well, he might look good now - but let's see how he does on a December weeknight in the League Cup at (insert name of lower league team with dilapidated ground and scruffy pitch) when it's -2 out and it's pissing down in sheets!'. --Kurt Shaped Box (talk) 23:06, 26 May 2010 (UTC)[reply]
There seem to be sport-by-sport conventions on this. Football (American football, you know, the real kind :-), like soccer, is not cancelled for weather unless it is truly extreme. Look up Ice Bowl, for example. But baseball games are delayed for any significant rain, and eventually cancelled if the rain doesn't stop. I'd be curious to know if that's also true for cricket.
This could be a safety thing, I guess — I really don't want a pitcher throwing a wet ball at me at 95 mph, especially when I might have trouble picking it up against the sky. --Trovatore (talk) 23:10, 26 May 2010 (UTC)[reply]
Cricket is usually called off if it starts raining significantly. The players go in and wait, the covers come on, then they maybe give it two or three hours and if it's still raining, the game/that particular day of the test is abandoned. --Kurt Shaped Box (talk) 23:20, 26 May 2010 (UTC)[reply]
Sounds about the same then (as baseball). I wonder whether this is convergent evolution (football and soccer have similar practical requirements, and so do baseball and cricket) or whether these are traditions that date back to the common ancestors of the two pairs of sports. --Trovatore (talk) 23:29, 26 May 2010 (UTC)[reply]
Having difficulty seeing the ball is usually due to poor light rather than rain (of course, rain can cause poor light, but it comes under a different clause in the laws of the game). If the bowler slips on the wet grass he can easily mis-bowl and end up bowling a beamer, which can break the batsman's arm. The ball bounces funny on wet ground too, but I guess they could learn to deal with that - I think it is the safety issues that causes them to pause the game. (It may also be because cricket is a sophisticated gentleman's game (they stop for tea and eat cucumber sandwiches made by the host team's wives) and they don't like getting muddy!) --Tango (talk) 01:01, 27 May 2010 (UTC)[reply]
Oh, right, tea and cucumber sandwiches. Just like baseball. --Trovatore (talk) 01:34, 27 May 2010 (UTC)[reply]
With cricket, I always assumed the main reason was so the pitch would not get wet. Getting a good wicket pitch seems almost like some sort of esoteric mystical art form, it has to be just the right hardness and dryness, with some cracks and not perfectly even thrown in too. I thought that getting the pitch soaked would make it just about impossible to bowl on. Vespine (talk) 02:27, 27 May 2010 (UTC)[reply]
The main reason for stopping play in cricket and baseball is that the two sides are doing very diffrent things during play. Its not fair if one team gets to bat on a dry pitch and the other side bats with a slippery unpredictable ball. Comparison of runs to determine victory in such a situation would be meaningless as it wouldn't tell you which team was actually better. In soccer its not an issue as both sides have to deal with the same problem.203.145.145.13 (talk) 07:54, 27 May 2010 (UTC)[reply]
Gamma Globulin/Is it available to the general public by prescription?
Is Gamma Globulin availble at this time to the general pubolic by prescriptiom?4annieiam (talk) 21:16, 26 May 2010 (UTC)[reply]
Depends on which one. Some are - but they are very very pricey. Ariel. (talk) 21:50, 26 May 2010 (UTC)[reply]
Gamma Globulin - used to treat Crohn's Disease
I was diagnosed with Crohn's Disease in 1972. After 6 months of treatment with Prednisone with less than adequate results, a doctor told me to try Gamma Globulin instead. He said 10% of Crohn's Disease patients responded to it. I tried it and it worked. I had no flare-ups until after 1991 when it was taken off the market.
The same doctor (in 1973)said that in earlier times there was medical literature about this use of Gamma Globulin. I looked at the Gamma Globulin information that was available at that time, but could find only one reference to it's use for Crohn's Disease, saying: 'Some people used to think Gamma Globulin could be used for the treatment of Crohn's Disease.'
My request is that if anyone can find medical information on the subject of Gamma Globulin used to treat
Crohn's Disease, probably written in the 1930's - 1960's, could they please post it to Wikipedia?
Google Scholar is wonderful for this sort of thing. You can do an advanced search for "Crohn's disease gamma globulin" and set the year range to 1930-1970. Lots of the hits even give you downloadable pdf files. Looie496 (talk) 21:47, 26 May 2010 (UTC)[reply]
Lots of books mention both search terms at Google Book search: [12]. Some of these are just noting gamma globulin levels in patients with the disease, rather than using it as a treatment. Many are "snippet views" and you would need to go to a university library or large public library to access the paper or books. Edison (talk) 21:52, 26 May 2010 (UTC)[reply]
BTW, Gamma Globulin is not a specific thing. It's a type of imunoglobin, but do you know which one you were given? Each one works against against a specific (different) target. Or were you given a random collection of them from a donor? Ariel. (talk) 21:53, 26 May 2010 (UTC)[reply]
Gamma globulin is more or less synonymous with immunoglobulin, IgG in particlular. Human immunoglobulin for therapeutic use is certainly not taken off the market. It is used for the treatment of immunodeficiency, and is also used for immunomodulation of various autoimmune diseases, such as immune thrombocytopenic purpura and Guillain Barré Syndrome. It is often administered intramuscularly for the treatment of immunodeficiency, and usually intravenously when the purpose is immunomodulation. In the latter case, it is often abbreviated IVIG (see the article IVIG). There is even a case report of immunoglobulin administered orally for the treatment of Crohn's disease [13]. However, we have probably already crossed the line regarding the reference desk's rules regarding medical advice that you can read on the top of the page, and I expect this thread will soon be deleted. I am writing this only to attempt to clear up what appears to be a misunderstanding. Apart from that, these are questions you should be discussing with your physician, not with random strangers on the internet. --NorwegianBluetalk 17:28, 27 May 2010 (UTC)[reply]
Touching car batteries
Is it possible to touch the two poles of a 12v car battery without considerable current passing through one's body? I remember someone messing the voltage with a large voltmeter and there were sparks but this doesn't make sense for such a low voltage. —Preceding unsigned comment added by 89.243.134.212 (talk) 22:17, 26 May 2010 (UTC)[reply]
The sparks are caused by the heating effect of the power flowing - car batteries can produce a large current - which is high enough to melt (and/or vaporise) thin wires or cause sparks. A high voltage isn't necessary for sparks produced on contact. A high voltage is only required for sparks (or 'arcing') with jumps across a long distance.77.86.125.207 (talk) 23:19, 26 May 2010 (UTC)[reply]
related is Welding power supply - arc welding uses "typically between 17 to 45 volts and 55 to 590 amps" - here the voltage is not much higher than a car battery and less than mains voltage - but look at the current.
This is different to that found in Electrostatic discharge such as found in lightning and which usually requires very high voltages. Both processes are similar.77.86.125.207 (talk) 00:12, 27 May 2010 (UTC)[reply]
The question dealt with whether much current would pass through your body if you touched both 12 volt battery terminals with fingers or whatever at the same time. Key issues are the contact resistance (dry or wet or broken skin, contact area), the part of the body the current is flowing through, and the bulk resistance of the tissues, Probably much lower than the contact resistance of dry skin. In movies, people are always getting tortured or electrocuted with 12 volt batteries. Let's just let potential murderers and torturers keep thinking that painful and dangerous current would always flow, whether it is true or not.45 volts (the arc welder comparison) is not 12 volts. Some cars have battery voltages much higher than 12 volts. In general, some current would flow, and even a small current could be dangerous to some people through some current paths. If a piece of jewelry like a ring or bracelet touched a positive wire and a grounded (negative) part of the car, serious thermal burns could result from the metal heating up, since high current would flow through that low resistance path. Edison (talk) 02:30, 27 May 2010 (UTC)[reply]
It's certainly possible for 12 V to create a current through the body. In most cases, I think that you wouldn't expect it to (dry skin makes a decent insulator). Here's a guy talking about electrocution [14]. If you search the article for "12V" (no space) you'll find where he talks about 12 V batteries. If you search "12 V electrocution" or similar in your favorite search engine, you'll find plenty of results. Consensus appears that it takes special circumstances for a 12 V battery to give you a good shock, but that it can happen. Burns from jewelry and such, as Edison pointed out, are also very much a hazard. Buddy431 (talk) 03:20, 27 May 2010 (UTC)[reply]
Touch the terminals of a 9 volt battery with your tongue and report back to us. 71.100.8.229 (talk) 08:49, 27 May 2010 (UTC)[reply]
I tried the tongue thing with the 9 volt battery. It works because your tongue is wet, making it a much better conductor. Here's something you can do. Take an ohm meter and clamp your dry hands to it. The resistance could measure about 100,000 ohms. Make your fingers moist: It may drop 500%. --Chemicalinterest (talk) 10:43, 27 May 2010 (UTC)[reply]
It's all very well to talk about how safe or otherwise this stuff is - but you really can do yourself some serious harm with even small amounts of voltage and current applied in just the wrong way. This 1999 Darwin Award went to a guy who died from a shock from a regular 9 volt battery. SteveBaker (talk) 18:03, 27 May 2010 (UTC)[reply]
Question about closed orbits
If two bodies are interacting in a gravitational field, and r is the position vector joining them, my textbook was able, by reducing the problem to a one body problem, to show that r would trace out an ellipse (if the orbit was closed). But do each of the bodies themselves move in an ellipse? And how can you show that the barycenter of the system is at a focus of any of these ellipses (that traced out by r, or the orbits of either body)? My textbook did say that if r started at the origin, then the origin would be a focus of r's ellipse, but I don't know if that has any connection with the problem(s). Thanks! 173.179.59.66 (talk) 22:22, 26 May 2010 (UTC)[reply]
Okay I think I was able to answer the first question: r1 or r2 will just be constant multiples of r, making them ellipses too. 173.179.59.66 (talk) 22:54, 26 May 2010 (UTC)[reply]
That derivation assumes that the Sun is much larger than the planet. 173.179.59.66 (talk) 23:38, 26 May 2010 (UTC)[reply]
So it does, sorry. Google will probably find you lots of derivations of Kepler's laws. --Tango (talk) 01:06, 27 May 2010 (UTC)[reply]
I've googled it but, sadly, they all do the same thing as Wikipedia, or as my textbook...173.179.59.66 (talk) 01:10, 27 May 2010 (UTC)[reply]
If you've already shown that r1 or r2 are constant multiples of r and the origin is a focus of r's ellipse then I think you're done. r1 and r2 measure the position of each object relative to the barycenter (or else they wouldn't be constant multiples of r, so that must have been an assumption in the derivation). So over time they trace out with respect to the barycenter two scaled versions of r with respect to the origin. Rckrone (talk) 02:44, 27 May 2010 (UTC)[reply]
Yeah, obviously, I don't know why I didn't see that. Thanks. 173.179.59.66 (talk) 11:54, 27 May 2010 (UTC)[reply]
Gravity express
I read online that if two points on the earth were connected via an underground tunnel, then (ignoring friction and rotation) the time it would take for a train to 'roll' between the two points would be independent of were the two points were located. I think the time came out to something like 41 minutes. Anyways, I tried to work out this is true but I wasn't successful...perhaps someone here will be? 173.179.59.66 (talk) 22:24, 26 May 2010 (UTC)[reply]
Assuming you are going to your antipode, This question has been asked here several times before, the last was here. It has links to previous discussions that might have the calculation. As gravity decays linearly as you move to the centre of the Earth (the part of the Earth that's above you reduces the gravity you feel), you need to use calculus rather than Newton's laws directly. CS Miller (talk) 22:35, 26 May 2010 (UTC)[reply]
No, apparently this is true of any two points, regardless of their distance apart. 173.179.59.66 (talk) 22:55, 26 May 2010 (UTC)[reply]
It is true. I think the best way to prove it is to use conservation of energy. Given that the train is at rest at the surface, its speed at any given point is a simple function of its distance below the surface (its kinetic energy is equal to the reduction in gravitational potential energy). Once you have the speed as a function of depth you can do some calculus to get the time taken and you'll find that it is constant. --Tango (talk) 23:11, 26 May 2010 (UTC)[reply]
(ec) Yeah I tried that, but the potential energy is a function of the distance to the center of the earth, while we need it to be written as a function of the distance travelled. I tried to relate the two, but I ended up with an integral that looked way to difficult to evaluate. 173.179.59.66 (talk) 23:35, 26 May 2010 (UTC)[reply]
Would this link help? Or was that what you used to get the ugly integral? --Tango (talk) 23:50, 26 May 2010 (UTC)[reply]
Q. Using the potential energy sounds like a good idea. But the (42 minute) solution seems to rely on the earth being solid, (ie not a point mass) - I can't find an equation for potential at distance r inside a uniform solid sphere - I'd be interested to know if it's easy to get one .. anyone know?77.86.125.207 (talk) 00:04, 27 May 2010 (UTC)[reply]
ok two points at the same distance from the centre of the earth. Assume the angle between them (and the centre of the earth) is theta , then , the angle the straight tunnel between them makes with the horizontal is theta/2. It's length is 2Rsin(theta/2). It's gravity that causes the train to roll. Like the link given above by Csmiller the motion is oscillatory. ie the start and end velocity is zero. You'll probably need to calculate the angle the tunnel makes with the gravitational force at each point along the tunnel so you can work out the component of that that causes the train to accelerate (or de-accelerate). I assume you'll also need the gravity inside the earth at radius r ; assuming a solid earth of constant density this is given by using the shell theorem - in fact this works out to be force due to gravity is proportional to r.
Did you try something like that and get stuck at solving the equations (you should get a differential equation for the motion eventually), or get stuck earlier or later? Probably the method described above by Tango is easier .. did you try something like that .. if so tell us where you got stuck.77.86.125.207 (talk) 23:31, 26 May 2010 (UTC)[reply]
Oh I completely forgot about the shell theorem...but anyways, if I understood what 77.86 said above, I tried that too but got stuck with the math. 173.179.59.66 (talk) 23:40, 26 May 2010 (UTC)[reply]
Yes the links from that article have derivations - similar to what I've attempted to describe below and probably easier to read. (they also don't mix up sin and cos like I did below . which helps. corrected now...) 77.86.125.207 (talk) 00:01, 27 May 2010 (UTC)[reply]
(edit conflict)
ok hint . at distance d from the surface along the tunnel the accelerating force due to gravity is proportional to r the distance from the centre of the earth and to the angle the line from the point to the centre makes with the path (call this angle alpha) - now can you see that the component of the force that causes acceleration is proportional to rcos(alpha) (r from shell theorem, cos(alpha) from the component of that force) .. now draw the construction for that value - you'll see that rcos(alpha) is equal to Rsin(theta/2)-d
( Rsin(theta/2) is half the length of the chord connecting the two points on the earth surface, and d is the distance travelled)
This makes the accelerating force linearly related to the distance the train has travelled (ie simple harmonic motion - just like a spring - and makes it a lot simpler to solve)
I think if you can get to the simple harmonic motion part you should find the rest easy. If you get stuck on the construction I've described above I'll have another go at explaining it, or upload an image)
I can see how it's easy to get stuck early on if you don't spot the simplification.77.86.125.207 (talk) 23:58, 26 May 2010 (UTC)[reply]
The statement that the time is independent of the initial and final positions is only true if curved tunels are not allowed. If curved tunels are allowed then the brachistochrone is the fastes path and will lead to shorter travel times for shorter distances between initial and final positions. this[15] shows a few examples. Dauto (talk) 04:13, 27 May 2010 (UTC)[reply]
Alright I got it, thanks a lot everyone. 173.179.59.66 (talk) 16:35, 27 May 2010 (UTC)[reply]
May 27
Cheetah speed
a cheetah is the fastest land animal and can achieve a peak velocity of 100 km/h upto a distance less than 500 m.if it spots its prey at a distance of 100 m then what is the minimum time it will take to catch its prey if the average velocity attained by it is 90 km/h ? —Preceding unsigned comment added by 117.205.176.131 (talk) 00:33, 27 May 2010 (UTC)[reply]
Probably not as fast as you could solve this simple math problem on your own. Please do your own homework. --Jayron32 00:37, 27 May 2010 (UTC)[reply]
Maybe the confusing part is the wording of the problem which is pretty bad! Assuming the subject is the cheetah every time they refer to "it" which makes more sense, this problem is very simple: How long does it take to travel 100m at a velocity of 90km/h. If you have a problem with this, you need to re read the chapter of your text book. Vespine (talk) 00:55, 27 May 2010 (UTC)[reply]
Do we need to account for the time it takes for the cheetah to accelerate to 90 km/h? I've also added a header ~AH1(TCU) 01:37, 27 May 2010 (UTC)[reply]
Nope. It clearly states "average velocity" which takes all changes into account, including the acceleration from stop. Its as simple as finding out how long it takes to run 100m at 90 km/hr. --Jayron32 01:44, 27 May 2010 (UTC)[reply]
You don't have enough information to give the minimum time. The prey could turn and run towards the cheetah, and you aren't told how fast the prey runs. --Trovatore (talk) 01:48, 27 May 2010 (UTC)[reply]
I remember getting questions this poorly worded all the time. Generally you are expected to make the fewest possible assumptions, if they didn't explicitly say the prey moves then you assume the prey doesn't move. It's a maths question not philosophy. The point about the prey and all that other stuff about top speed and 500m and all that are red herrings there to throw off the "logical" part of your brain. ;) Vespine (talk) 02:02, 27 May 2010 (UTC)[reply]
I assumed that the second "it" referred to the prey, and the prey attained a speed of 90 km/hr, with the cheetah chasing it at 100 km/hr, in which case the question is quite different (though still easily solvable). It is a poorly worded question, though. Buddy431 (talk) 03:06, 27 May 2010 (UTC)[reply]
But the 100 km/hr is stated as a peak velocity Nil Einne (talk) 03:31, 27 May 2010 (UTC)[reply]
That's the bad wording i was talking about. I think it makes more sense if you just assume the cheetah as the object of the question all the way through. Any time it says "it" or "its" assume cheetah. I think the question is essentially "How long does the prey initially have to react if the cheetah starts from 100m and can obtain an average speed of 90km/h over that distance." Vespine (talk) 04:14, 27 May 2010 (UTC)[reply]
An interesting thought, Cheetahs like to trip their prey as it runs. Would they even go after an gazelle that stands its ground? 65.121.141.34 (talk) 13:10, 27 May 2010 (UTC)[reply]
Two methods, two solutions
You have identical objects at 300K, 300K, and 100K that are perfectly insulated from their surroundings. Using heat engines, what's the highest temperature to which any object can be raised?
If you assume that the 300K and 100K objects do work on the other 300K object at the Carnot efficiency, you get 354K. If you assume that the change in entropy is 0, you get 400K. Both approaches seem equally valid to me. Why do they give different answers? --99.237.234.104 (talk) 01:11, 27 May 2010 (UTC)[reply]
I don't fully understand your question, but heat pumps (is that what you mean by heat engine?) waste energy - so does that wasted energy count toward raising the temperature? Ariel. (talk) 03:08, 27 May 2010 (UTC)[reply]
Would you care to share your calculations with us to make our job of pinpointing any mistakes a little easier? Dauto (talk) 04:46, 27 May 2010 (UTC)[reply]
The calculations are quite simple, but long and tedious. Anyhow, here they are.
The entropy method: Suppose the final temperature of one 300K one 100K objects is T1. Suppose the other 300K object is raised to T2. 2T1+T2=300+300+100=700 due to conservation of energy. dS=dQ/T=c*dT/T=clnT, so for all three objects, the condition that total entropy change = 0 is equivalent to lnT1/100 + lnT1/300+lnT2/300=0. Solving the two equations gives T2=400K.
The brute force method: Suppose a 300K and a 100K object are used as the heat source and sink for a Carnot engine, and that the engine's work is used to raise the other 300K object's temperature. W=Qh(1-Tc/Th) and Qc=Qh*Tc/Th for a Carnot engine. Qc=Qh*Tc/Th is equivalent to -c*dTc=c*dTh*Tc/Th, or dTc/Tc=-dTh/Th. Solving this gives Tc*Th=T1T2, where T1 and T2 are the initial temperatures (100K and 300K). W=Qh(1-Tc/Th) is equivalent to dW=-c*dTh*(1-T1T1/Th^2). Solving this equation gives W=c(sqrt(T1)-sqrt(T2))^2. Setting this equal to the heat absorbed by the other 300K object, c*delta-T=c*(sqrt(T1)-sqrt(T2))^2 and delta-T=(sqrt(T1)-sqrt(T2))^2. This gives delta-T=54 degrees and final temperature=354K. --99.237.234.104 (talk) 05:07, 27 May 2010 (UTC)[reply]
The first method is not correct. The carnot cycle is reversible and does not increase the entropy but the subsequent conversion of the work produced by the cycle into heat delivered to the third system is not reversible and does increase entropy. dS=0 is incorrect. Dauto (talk) 05:55, 27 May 2010 (UTC)[reply]
On a second thought, if you are also allowed to use heat pumps (which are nothing more then heat engines running backwards), then it is possible to dump the work in the third body reversibly by pumping heat from one of the colder bodies into the hot one using the work extracted from the heat engine attached to the two fist bodies. If you are allowed to do that then the first method gives the correct answer. Dauto (talk) 14:33, 27 May 2010 (UTC)[reply]
Thank you, that makes sense. Yes, you're allowed to use heat engines, heat pumps, refrigerators, and absolutely anything else in the world except outside energy. --99.237.234.104 (talk) 03:27, 28 May 2010 (UTC)[reply]
Agreed, it's crushed red pepper. Comet Tuttle (talk) 23:08, 27 May 2010 (UTC)[reply]
reproduction in plants
Life span of May fly is 01 day while that of Banyan tree can be 200 yrs. What message do
you get from this data concerning BMR (Basic Metabolic Rate)? —Preceding unsigned comment added by 180.215.248.143 (talk) 08:35, 27 May 2010 (UTC)[reply]
Nothing. I get no message about BMR from that at all. Ariel. (talk) 08:50, 27 May 2010 (UTC)[reply]
Adult mayflies may only live for a day but their larvae live for several years. Plants do have a lower metabolic rate compared to animals as they don't have to move. Have you read Metabolic_rate#Longevity? Incidentally 200 years is nothing - check out the bristlecone pine. 86.7.19.159 (talk) 09:08, 27 May 2010 (UTC)[reply]
terminology for the concept of group immortality
. What is the terminology for the concept of group immortality? —Preceding unsigned comment added by 180.215.248.143 (talk) 08:37, 27 May 2010 (UTC)[reply]
Hu? I don't understand the question, please rephrase it. Ariel. (talk) 08:50, 27 May 2010 (UTC)[reply]
The collective term would be "immortals" ?77.86.125.207 (talk) 10:01, 27 May 2010 (UTC)[reply]
Synthetic life: human health-care implications?
Could the recent "digitally programmed" loops of DNA used to create synthetic bacteria be scaled up to create and repair the complex DNA in a human, for example to create new heart or hair cells? Or are macroscopic problems in tissue engineering a bigger block to replacing damaged body parts? [Trevor Loughlin]80.1.88.1 (talk) 10:43, 27 May 2010 (UTC)[reply]
I think we're far too early in this technology to really know what it's total health care potentials will be or whether there will be insurmountable difficulties. Don't expect to see direct health care implications for another 10-15 years, which is the general turn-around time for cutting edge technology before it becomes something "tamed" enough to start using in actual patient settings. --Mr.98 (talk) 13:17, 27 May 2010 (UTC)[reply]
Technology to create or regrow damaged body tissue already exists, though it too is still in its infancy. — Ƶ§œš¹[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi] 17:37, 27 May 2010 (UTC)[reply]
How can chlorine be used to oxidize selenious acid to selenic acid, itself being reduced to chloride ions? The article also says that selenic acid can oxidize chloride ions to elemental chlorine. Is it an equilibrium? Thanks. --Chemicalinterest (talk) 12:30, 27 May 2010 (UTC)[reply]
The article clearly states you have to remove the HCl byproduct to drive the reaction. The statements have footnote references. One of them, a free abstract of an article, states that there is also a temperature effect. DMacks (talk) 15:12, 27 May 2010 (UTC)[reply]
The reaction must be an equilibrium since it is described going both ways, the textbook source - available in part on line gives no further clues see page 54477.86.125.207 (talk) 16:57, 27 May 2010 (UTC)[reply]
speeding
whats a good place to take my car up to 100 mph ? i tried my street late at night when no one was around but its not long enough i only get up to 70 mph. i dont want to do it on the highway cause i might get pulled over. whats a good secluded place to go to 100 mph ? —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:40, 27 May 2010 (UTC)[reply]
Find a sanctioned dragstrip in your area if you think 1/4 of a mile is enough distance to get up to the speed you want. Outside of that you have few legal options unless you want to drive to a dry lake. --Jmeden2000 (talk) 13:51, 27 May 2010 (UTC)[reply]
FWIW, you will need a car with very good acceleration to get up to 100 in a quarter mile. My, uh, friend, has had luck using short spurs between highways where they don't bother with speed traps. In a place where this was perfectly legal, of course. Also is your car in good shape? How are your tires and brakes? You don't want to travel at high speeds in a car that's not up to the job. Friday(talk) 13:59, 27 May 2010 (UTC)[reply]
Along the lines of illegal options, though, trying this on the highway is much much safer than on surface roads. You'd be on a road more closely intended for 100 MPH and driving in one-way traffic moving more closely to 100 MPH. The former means you're less likely to have a one-car accident, and the latter means that in addition to reducing the chance of a two-car accident, you'll put the closing speed of the collision closer to 30 MPH than to 130 MPH. Finally, in the event that the police take notice of you, you'll all but certainly get more lenient treatment trying this on the highway. Now, all that said, follow Jmeden's advice above and find a dragstrip. And absolutely never try this again on a two-way street. — Lomn 14:05, 27 May 2010 (UTC)[reply]
Go to Germany and drive on the Autobahn on a day where the traffic is incredibly light. They have no speed restriction there, assuming it is considered safe to do so. It's recommended you don't go above 85mph, but they aren't going to pull you over because you're doing more. 14:14, 27 May 2010 (UTC)Regards, --—Cyclonenim | Chat
I think it is an incredibely irresponsible thing to try to speed to 100mph in a city street late at night. I sincerely hope the police pulls you over. Dauto (talk) 14:23, 27 May 2010 (UTC)[reply]
it wasent a city street it was a residential street at like 3 am no one was on it. —Preceding unsigned comment added by Tom12350 (talk • contribs) 14:28, 27 May 2010 (UTC)[reply]
Yeah, yeah, yeah... I hope you get pulled over. Dauto (talk) 01:06, 28 May 2010 (UTC)[reply]
Wow you aren't going to win friends with that argument... not to sidetrack this but people (like me) from time to time walk their dogs late at night (even at 3am) and would enjoy not having to dodge a car going ~100mph... At that speed you likely won't likely realize your observation of "no one was on it" was wrong until they are under your car. --Jmeden2000 (talk) 14:32, 27 May 2010 (UTC)[reply]
Additionally at speeds like that your margin of error is very low, and being surrounded by houses full of people is pretty dangerous. A residential area has a lot of people and a lot of property in it. Don't drive recklessly there even at 3am (when there are more people around than you probably realize). Go somewhere where there aren't any people at all so that if you lose control and total your car you don't kill anyone else in the process. In these situations it is not the "normal" that you prepare for and worry about, but the freak accident. Take some responsibility. --Mr.98 (talk) 14:47, 27 May 2010 (UTC)[reply]
i drove down the street first to make sure no one was walking and it also had a sidewalk. im not here for a moral lesson just give me advice how to do it. what do you mean by "short spurs between highways where they don't bother with speed traps. " where is that. —Preceding unsigned comment added by Tom12350 (talk • contribs) 14:42, 27 May 2010 (UTC)[reply]
On a residential street you're probably going three times the speed limit. If they catch you doing that, they won't bother writing a ticket. Your car will be towed and impounded, and you'll be handcuffed and put in prison. (Question : Are you certain that no one living in that neighborhood is a cop? Would you bet the next couple years of your left on it?) APL (talk) 15:58, 27 May 2010 (UTC)[reply]
Well I've had my car up to 100 mph on a UK motorway (quite by accident - I'd just bought it and didn't realise I didn't have to have my foot down as far as I was used to in my old car, your honour). I don't think you're in the UK though! Seriously, don't drive at that speed in a built-up area. While there may not be people walking around, if you lose control of your car (and at that speed it's ludicrously easy - maybe hitting a kerb will do it) then you may well land at first floor level in someone's house. I'm pretty sure they won't appreciate being woken by some twat parking a car in their bedroom - and I'm also pretty sure you wouldn't be alive to hear them scream at you for doing it. --TammyMoet (talk) 14:58, 27 May 2010 (UTC)[reply]
Find a local Track day event, and do it safely and legally. A residential area at 3am is the worst idea, people going out are likely to be making emergency trips (sick kid on the way to hospital), walking the dog, or cycling because its cool and safe. -- Q Chris (talk) 15:07, 27 May 2010 (UTC)[reply]
I recommend I-76 in eastern Colorado. A cop followed me for a couple miles (I was driving 95 mph) and finally just passed me. There is pretty much nobody out there. One thing to note, the road is not great, and I was not comfortable going above 110 on it. 65.121.141.34 (talk) 15:17, 27 May 2010 (UTC)[reply]
If you're determined to do it illegally, I don't see what the big deal is. Go out on the freeway and do it. You didn't need us to tell you that a good place to drive fast is the freeway? Surely you've noticed that a lot of people seem to do 80-90 on a regular basis? APL (talk) 15:58, 27 May 2010 (UTC)[reply]
You drove down a residential street, saw no one so you presumed there was no possibility someone would be out on the road at that time? You aren't aware then that people live in houses and yes, they do sometimes come out of their houses at 3 am and walk along their street after you 'checked for people', and no, they don't monitor to see if there's some person driving along the street to check if people are walking and presume that said person is later going to drive along the street at 100mph so they should wait until said person has finished driving along the street particularly given that said person doesn't sound like the sort of person likely to be able to safely drive at 100 mph so could easily lose control and kill them for the 'crime' of walking along the street after said person had driven along the street to look for people (or perhaps simply not being seen by said person).
Or for that matter you never considered that you could lose control and hit a house killing someone in it in process (not outside the realms of possibilities if you're driving at 100mph).
And yes, it is personal because although I don't live in the US so thankfully I'm unlikely to ever meet the OP, I do sometimes go out late at night (I don't drive so I'm either walking or cycling) and while I'm aware there are always going to be some risks, it's quite a different thing to meet someone who openly admits he's one of those security risks to people like me. Since I'm usually going to some shopping complex the latest tends to be slightly after midnight since that's the latest their open here, at Christmas time but it's always possible I would go out at that time, why shouldn't I? But apparently people like me don't matter because hey I wasn't supposed to be out so late and if I was I was somehow supposed to make sure people like the OP see me before they go driving along the street at 100mph. So don't bother telling me off for WP:NPA or WP:Civility, this message is well and truly deserved.
what do you mean by "short spurs between highways where they don't bother with speed traps. " —Preceding unsigned comment added by Tom12350 (talk • contribs) 17:44, 27 May 2010 (UTC)[reply]
See Spur route. I'm not sure what the difference is between a Spur Route and a Connector. It may just be regional dialect.
I'm not confident that they're necessarily ignored by highway patrol. APL (talk) 20:04, 27 May 2010 (UTC)[reply]
While it depends on the highway, your local police and other factors, if you regularly drive along a highway you are probably aware of the favourite spots for cops so the OP's best bet is to find one of them and try it. Perhaps a spur route perhaps just a part of the highway that doesn't tend to be monitored much (perhaps far from the main urban areas). Ultimately as APL said earlier, if you're determined to do it illegally, you can't expect a guarantee you won't be caught. Nil Einne (talk) 20:13, 27 May 2010 (UTC)[reply]
Please don't ever again do anything idiotic like drive at 100mph down a residential street, no matter whether or not you think there's nobody there. You may not know that in the US, in most states, exceeding 100mph is a felony, and I would hope the prosecutor would pile on charges of reckless endangerment and actually send you to prison for 3-5 years. Comet Tuttle (talk) 23:12, 27 May 2010 (UTC)[reply]
Applied Logic - What is this?
Do you have any idea what this sign means? In cleaning out my lab, I found it behind a solvent locker. It may have been there for decades. ike9898 (talk) 15:08, 27 May 2010 (UTC)[reply]
The first thing to decide, is whether its supposed to read
"not quite physics envelope but close" or
"not quite envelope physics but close".
I'd say the spacing is ambiguous, it could be read either way. Googling "envelope physics", yields almost exclusively hits containing "back of the envelope physics", which doesn't seem to make much sense without the introductory "back of the", at least not to my non-native ears. Googling "physics envelope", on the other hand, yields hits like "Adult tarantulas are pushing the physics envelope with exoskeleton size & so are very susceptible to damage from falls", there's a Nature article called "pushing the physics envelope" (which I can't read now, as I'm writing from my home PC). Another hit reads: "Does no one push the Physics Envelope anymore? Have we really reached the highest point in the helicopter design...". So it appears to me that "physics envelope" means "limits of what physics can achieve".
So I'd interpret it as: APPLIED LOGIC gets you not quite to the limits of what physics can achieve, but close. --NorwegianBluetalk 16:04, 27 May 2010 (UTC)[reply]
I think it is likely that it is supposed to read "not quite envelope physics but close, with "back of the envelope physics" being what it is referring to. See back-of-the-envelope calculation, it means "a rough calculation", as doing physics on the back of an envelope is less accurate than using a computer or something. So, applied logic is not quite as (in)accurate as doing physics calculations on the back of an envelope, but it is close. I guess somebody didn't like applied logic. --Cerebellum (talk) 16:40, 27 May 2010 (UTC)[reply]
I agree with the above (2 makes sense) ie
Hitting things with clubs < Handwaving < Applied logic < Back of envelope calculations < Full solution of multi-electron shrodinger equation ..etc...77.86.125.207 (talk) 17:01, 27 May 2010 (UTC)[reply]
Question - did the department you're at used to have an "Applied logic department"? - might have been a joke comment on the quality of research they did there , or something.77.86.125.207 (talk) 17:02, 27 May 2010 (UTC)[reply]
This building is highly interdisciplinary, and changing all the time, so figuring out if applied logic was being used at some undefined point in the past would be a significant task. ike9898 (talk) 18:52, 27 May 2010 (UTC)[reply]
"Envelope physics" means "physics that pushes the envelope" -- the envelope being the boundary between the possible and the impossible. So it's basically a bit of humor that means "we're not quite out at the bleeding edge but we're close to it". Looie496 (talk) 17:44, 27 May 2010 (UTC)[reply]
I'm not sure this discussion has converged on a single explanation, but I've certainly got a better idea than I did before. Thanks, everyone! (Further thoughts welcome) ike9898 (talk) 19:00, 27 May 2010 (UTC)[reply]
How is temperature controlled onboard a commercial airplane ? I'm guessing that they lack heaters and A/C, but rather use the excess heat from the jet engines and the cold from the air at altitude to control temps. However, neither of these are available on the ground, and this might explain why the passenger compartment quickly overheats when a plane is stuck on the ground. (I suppose it could also get cold in very cold weather, at night, with an almost empty plane, where solar heating and heat given off by passengers would be minimal.) Also, has there been any thought to providing a truck that could drive out to a plane stuck on the tarmac, and hook it up to provide an external A/C or heat source ? Obviously the plane would need some place to connect to. I suppose the passenger door(s) could be opened and air could be pumped in one flexible duct and out another. I was on a plane that was only stuck like this for 15 minutes, and it got hot, so I wonder just how hot they get after many hours like this ? I've also noticed that they don't seem to overheat when parked at the gate, so do they have some external hook up they use to prevent this from happening there ? StuRat (talk) 16:47, 27 May 2010 (UTC)[reply]
Commercial airliners do have air conditioning units. Heating is achieved with an engine-bleed heat exchanger. When an aircraft is on the ground, with the main engines not running (but with passengers boarded), the auxiliary power unit is run, which has the same effect - even the APU has enough juice to run both heating and A/C. When at the stand, some airports have power hookups. I too have spent some uncomfortable time at EWR in the Summer on a plane with no APU at a stand with no hookup. After a (long) while they came up with some truck, which I think had a generator to do the job of the APU. Refs: http://www.b737.org.uk/airconditioning.htmhttp://www.boeing.com/commercial/cabinair/ecs.pdf -- Finlay McWalter • Talk 17:23, 27 May 2010 (UTC)[reply]
Gregory-Madhava Series
(moved to Ref Desk/Math) --pma 18:15, 27 May 2010 (UTC)[reply]
Fungus
“Any organic material kept in moist and dark conditions gets infected with fungus,
although there was no sign of fungus prior to it.” How fungus does make it possible,
although it is a microbe? —Preceding unsigned comment added by 180.215.248.62 (talk) 18:20, 27 May 2010 (UTC)[reply]
I heard that mold spores are floating all over in the air. When they find a good environment, they attach to it and multiply. --Chemicalinterest (talk) 18:34, 27 May 2010 (UTC)[reply]
The original statement is clearly untrue - there must be either fungus or fungal spores in the air or in the original organic material in order for a fungus 'infection' to happen - in which case, the statement that "there was no sign of fungus prior to it" must be false. Perhaps there were no visible signs - but under close enough analysis, some kind of fungal material had to be present at the outset. SteveBaker (talk) 20:07, 27 May 2010 (UTC)[reply]
I think it means no visible sign, since there are always fungal spores around. We're all exposed, all the time, to to fungal spores, and if they do find somewhere moist area then they can settle. I don't see how dark conditions matter, fungi aren't damaged by light, at least not any of the fungi I've heard about. Regards, --—Cyclonenim | Chat 21:22, 27 May 2010 (UTC)[reply]
First of all, fungus is not the same as a microbe (microorganism). More precisely, some fungi are microorganisms, and some are not; some microorganisms are fungi, and some are not. Second, as people have already said above, fungi do not "spontaneously generate", they grow from spores. The theory of Spontaneous generation has indeed been disproved for at least 200 years now. (On the other hand, the life on Earth may well have spontaneously generated in the first place; but that took a few billion years, see abiogenesis; and the first life forms were certainly nothing like the modern fungi). Third, not all organic material kept in moist and dark conditions gets infected with fungi. See putrefaction, decomposition, saponification, and fermentation. --Dr Dima (talk) 21:38, 27 May 2010 (UTC)[reply]
I don't think saponification has anything to do with fungi? or very much to do with stuff going off in the pantry?77.86.125.207 (talk) 23:09, 27 May 2010 (UTC)[reply]
smoke
wouldent the people in this vid get really stoned from the smoke in this vid
(This is a vid of opiumpoppies being destroyed by burning them.) I think that a: people are not standing in the smoke, and b: the flames might be hot enough to destroy the active ingredients. Regular smoking is not a flame, but rather embers which are cooler than a flame. Ariel. (talk) 21:45, 27 May 2010 (UTC)[reply]
Note that the burning includes all parts of the plant - not just the resin that contains the opium - thus it would be unpleasant to breath in. (like inhaling the smoke from burning straw). 77.86.125.207 (talk) 23:08, 27 May 2010 (UTC)[reply]
Lead dissolution
How would you dissolve lead metal to form lead salts using household chemicals? Thank you. --Chemicalinterest (talk) 19:08, 27 May 2010 (UTC)[reply]
I would guess that bleach would do it, especially in the presence of strong base, which solublises both Pb2 and Pb4 salts.
The reaction is postulated as being a possibility in the corrosion of lead pipes [16] , but doesn't seem to be certain.77.86.125.207 (talk) 19:31, 27 May 2010 (UTC)[reply]
Alternatively a route to lead oxide (which should readily react with acids to form salts) - is by heating and stirring molten lead to effect the oxidation of lead - which can be removed from the surface.
You know lead is considered poisonous in general?77.86.125.207 (talk) 19:33, 27 May 2010 (UTC)[reply]
In theory, any acid should react with lead to form salts, such as:
Pb + H2SO4 → PbSO4 + H2
However, lead is just above hydrogen on the reactivity series, so an acid-lead reaction could take a very long time. --The HighFinSpermWhale 19:37, 27 May 2010 (UTC)[reply]
I have some ancient lead solder that I dissolved in hydrochloric acid, leaving the lead and rosin behind. (I used the tin(II) chloride formed as a reducing agent). I was wondering if there was any way to form lead compounds from the lead powder left behind. --Chemicalinterest (talk) 20:08, 27 May 2010 (UTC)[reply]
What about using acetic acid from vinegar? Lead(II) acetate is well known and can apparently be synthesised by reaction of acetic acid with lead(II) oxide, PbO. You could first convert Pb to PbO by blasting it with a blowtorch or something.
No blow torch needed. As you have already lead powder you have a high surface area - the surface should be lead oxide already - dissolve the surface layer with acid, filter, wash, allow to dry - divide the powder again (allow time for another oxide layer to form) .. repeat. However this will produce finer and fine lead powder - which is not a good idea health wise.77.86.125.207 (talk) 21:06, 27 May 2010 (UTC)[reply]
Is the reducing properties of sodium amalgam relevant to the sodium content, or the mercury being in a negative valence. Or is it considered covalently bonded? --Chemicalinterest (talk) 20:15, 27 May 2010 (UTC)[reply]
The reducing power will always increase with concentration.. (avoiding the issue of what the thing in sodium amalgam actually is .. article claims Na2Hg - but I wouldn't count on it.) 77.86.125.207 (talk) 21:31, 27 May 2010 (UTC)[reply]
Possibly different compounds will be formed depending on the amount of Na [17] - suggests NaHg , Na2Hg ,Na3Hg -not sure if this is right - there are definately a lot of different species [18]
Na2Hg definately exists and is an Intermetallic - it's somewhere between a normal metal alloy and a salt - may look like a 'shiny ceramic'. The bonding can be considered primarily metallic (which is similar to a non directional covalent bond) but with polar character too - additionally the structures of isolated amalgams may not have all that much bearing on what may often be a solution of Na in Hg (or a mixture of different sodium/mercury intermetallics)- you coukd think of it as simply Na in solution in Hg, with some charge transfer from the Na to the surrounding Hg's - which will form a coordination shell similar to that found when Na+ is in solution in water solvated to Hg (it wouldn't affect the understanding of the redox chemistry much)- in general the actual situation in any Na/Hg mixture is complex.77.86.125.207 (talk) 21:38, 27 May 2010 (UTC)[reply]
The main thing to remember is that its action is by electron transfer, and that the electrode potential is not the same as that of pure sodium (amalgam is less reducing).
Crocodile Poo
We posted here earlier, but were unfortunately dismissed. Allow us to rephrase our question so that your dilettantes are able to understand, and can hopefully help without deleting this post. Do crocodiles leave solid excrement or do they lose waste primarily through the skin and fluids. THANK YOU. —Preceding unsigned comment added by 129.67.38.99 (talk) 22:15, 27 May 2010 (UTC)[reply]
Your google search helps very little. —Preceding unsigned comment added by 129.67.39.207 (talk) 23:17, 27 May 2010 (UTC)[reply]
You're supposed to click on the links and read them.77.86.125.207 (talk) 23:22, 27 May 2010 (UTC)[reply]
Given that people respond to you out of their goodwill, you could be a bit nicer, though when all google search returns are fosilized crap one may indeed wonder how that helps to find out something aout modern animals. The thing with crocodiles and such is that those are not animals of one species and charecteristics of diffrent spiecies may vary. The article says that they have no urine bladder, so it is more likely they don`t urinate. The fact that there is fosilized shit and unusal characteristics (such as getting rid of all the waste products by other means than shit) usualy are pointed out suggests that they shit. Also if you google crocodile anatomy you`ll notice that they have a cloaca, which is meant for sex, shit and urine, by looking up that, I found site on captive care of crocodiles, maybe you`ll find something there as people who keep them are quite likely to get up close and personal with crocodile shit, if it exists, their guide on determening the pet`s sex hints that they may shit if someone examines their butts [20] ~~Xil (talk) 23:56, 27 May 2010 (UTC)[reply]
Unless your results are majorly different from me, you don't even need to click the links. The fact that a book is talking about "Coronavirus Coronavirus-like particles were found by transmission electron microscopy in negatively stained faeces of four 2-3-year-old crocodiles from a ..." [21] and a research paper is talking about "found by electron microscopy in the faeces of farmed Nile crocodiles in South Africa" [22] and a FAQ on Crocodilian Captive Care says "The stool can often be very soft and difficult to collect - a croc's digestive system is very thorough. The faecal sample will enable the..." [23] and someone in a journal says "One of the highlights of this hour is to have pointed out to us crocodile faeces!" [24] is evidence enough that they shit. So I don't understand how the Google search 'helps very little' to anyone who bothered to actually take a glance thru it. And that's even if you ignore the fossilised faeces Xil discusses above that there are images of and is mentioned in "The 15 million year-old fossilised faecal matter, or coprolites, are each the size of a fist and bear clear impressions of prehistoric shark ..." [25] what's the second link for me. Of course, if you have any abouts that these are talking about crocodile faeces, you can click them to see it in context. Nil Einne (talk) 00:08, 28 May 2010 (UTC)[reply]
Satellites and relativity
If you know the height of a satellite above the Earth (h) and you also know the velocity with which the satellite rotates around the Earth (v) what calculation do you perform to determine the offset of the clock aboard the satellite due to the combined effects of special and general relativity?--Wikinv (talk) 02:26, 28 May 2010 (UTC)[reply]
I don't think there are any general relativity effects. The satellite is in free fall, so it's experiencing no acceleration (force). All you have is velocity, and of course that only has meaning in comparison to something, presumably the earth. The interesting part is that the earth is experiencing general relativity effects due to it's gravitational field, not the satellite. Ariel. (talk) 03:21, 28 May 2010 (UTC)[reply]
dam people
Paraphrasing Ronald Regan as "Seen one tree, seen them all." where would be the best places to dam up the Grand Canyon and how much energy from fossil fuel be replaced? 71.100.8.229 (talk) 02:31, 28 May 2010 (UTC)[reply]
