Wikipedia:Reference desk/Archives/Science/2012 August 25

= August 25 =

What if Earth stopped rotating?
Assume that its rotation is slowed gradually enough that the deceleration doesn't cause any major effects. --168.7.232.12 (talk) 00:35, 25 August 2012 (UTC)
 * We get this question a lot. If I may quote myself, from March of this year, when I quoted myself from a similar question in September of last year: (I have taken some liberties to modify the quote to increase relevance to the current question)
 * The answer to this type of physics question always depends: how would [the earth stop spinning]? If you can specify that, we can follow through with the consequences by solving the equations of motion for the Earth-Moon[-Sun] system.

For example, if you hypothesize that a giant comet large and fast enough to change the [Earth's rotation] impacted our planet, .... well, we would need to calculate the effect that such a large comet has on the orbits of Earth and everything else in the solar system, too. We could solve that problem by setting up an n-body problem to model the solar system, including Earth, Moon, Sun, and other planets; and we would use perturbation theory to study how sensitively the system reacts when we add in a new comet on a course to impact the moon. The results are difficult to compute, but this can be done in a reasonable amount of time with a reasonable amount of effort.

...

On the other hand, if you just want to make something up, "just imagine" that the [Earth] magically changes its [rotation], all bets are off. We can't meaningfully speculate what consequences follow when one law of physics breaks "because of magic." Anything could happen. Everything we know about the way the Moon's orbit couples into the Earth's rotation depends on the rules of physics as we currently understand them.
 * So - does that answer your question? Anything.  Anything could happen.  Nimur (talk) 01:00, 25 August 2012 (UTC)
 * So, hold on, how does a comet on a course to impact the moon cause the Earth to stop rotating? 203.27.72.5 (talk) 01:14, 25 August 2012 (UTC)
 * In general, it does not. You could conceivably concoct some unusual special circumstance where the angular momentum of the comet and the Earth's rotation were perfectly matched up so that it would cancel to zero after a collision, and then solve for the necessary conditions that would make such an impact possible.  Nimur (talk) 04:06, 25 August 2012 (UTC)
 * I still don't see why the moon is coming into this... 203.27.72.5 (talk) 04:09, 25 August 2012 (UTC)
 * Also, my original comment was addressed to a similar question, linked above, about the moon ceasing to revolve around Earth, ... so that might be the source of the confusion. Nimur (talk) 04:11, 25 August 2012 (UTC)


 * The OP specified a gradual slowdown. At the very least, doesn't the rotation help distribute the heat through the atmosphere? If so, wouldn't the same side facing the sun all the time cause big-time trouble? ←Baseball Bugs What's up, Doc? carrots→ 04:59, 25 August 2012 (UTC)
 * Well, that raises an interesting problem to figure out, and that is what does "stop rotating" mean. Stop rotating relative to the sun (i.e. the solar day) or stop rotating relative to the background stars (i.e. the sidereal day)?  In the former case, the same side faces the sun all the time (this is roughly what Mercury does, IIRC), but from an observer hanging outside the solar system, the earth would turn very slowly in order to maintain that same side facing the sun.  In the latter case, the sun will rise and set (from the earth's perspective) over the course of a year, but an outside observer would view the earth as not rotating at all.  Yet another complication from the poorly thought out question... -- Jayron  32  05:10, 25 August 2012 (UTC)
 * Mercury rotates at a rate such that the sun (roughly) stops at perihelion when the tide is strongest. —Tamfang (talk) 00:39, 26 August 2012 (UTC)


 * Um, Bugs, if the Earth 'stopped rotating', the same side wouldn't face the sun all the time, given that the Earth goes round it once a year... AndyTheGrump (talk) 05:07, 25 August 2012 (UTC)
 * OK, "stopped rotating" in relation to what? The Andromeda galaxy, perhaps? ←Baseball Bugs What's up, Doc? carrots→ 05:09, 25 August 2012 (UTC)
 * Ooo, can somebody link to that thought-experiment about a bucket of water rotating, and what it is rotating relative to? I can't remember what it was called, but I seem to recall that serious scientists disagreed and it included Einstein's opinion somewhere. 86.169.212.200 (talk) 14:42, 25 August 2012 (UTC)
 * I don't know a good link (I read about it in a book) but it is a very interesting thought experiment. The idea is that you can tell if a bucket of water (or just two masses joined by a pieces of string) is rotating just by looking at the shape of the surface of the water (if it is rotating, the surface will be curved), without reference to anything external. The question is then what happens to a bucket in an otherwise empty universe. It is meaningless to ask whether it is rotating or not because there is nothing for it to rotate relative to, so is the surface of the water curved or flat? (Or, is the pieces of string taut or slack.) I'm not aware of there being a generally accepted answer. --Tango (talk) 19:49, 25 August 2012 (UTC)
 * Bucket argument is the article. See also Mach's principle. -- BenRG (talk) 22:09, 25 August 2012 (UTC)


 * There was some National Geographic mockumentary about this idea, which I assume is where all the questions come from. I might offend the local copyright clergy if I post a link, but let's just say that "Aftermath: When the Earth Stops Spinning" is abundantly known to YouTube.  See also  Wnt (talk) 12:43, 25 August 2012 (UTC)

However improbable stopping Earth's rotation is, we can still describe what conditions on Earth would be like. Assuming that the Earth becomes tidally-locked to the Sun, the Sun-facing side would be very hot, the far side very cold. This would induce powerful winds flowing along the surface from the dark side to the Sun-side, with high altitude winds in the opposite direction. It is likely that there will be a zone, with the Sun low on the horizon, where there would be begin conditions for human life. However, it is likely that most life would find it hard to adapt to 24hr sunlight, with no seasonal variation. CS Miller (talk) 14:04, 25 August 2012 (UTC)
 * If we're ignoring the physical effects of the transition, we can certainly ignore the biological effects. The idea of life living near the terminator on a tidally-locked planet has been explored in science fiction, but it would probably be difficult for complex life to thrive in such an environment. Simple life (bacteria, etc.) living underground where the extreme climate can't affect them should be fine, though. --Tango (talk) 15:11, 25 August 2012 (UTC)
 * But if the Earth became tidally locked to the Sun, then it wouldn't have stopped rotating: its rotation speed would be a year. If the Earth really stopped rotating, then one day would last a whole year, and you'd have six months of daylight and then six months of night (if I'm thinking correctly). Double sharp (talk) 05:39, 26 August 2012 (UTC)


 * I was going to say they would need to cancel As the World Turns, but they apparently already did so, preemptively. :-) StuRat (talk) 20:06, 25 August 2012 (UTC)

The Earth's rotation is already slowing due to tides and the expanding orbit of the moon. μηδείς (talk) 02:12, 26 August 2012 (UTC)

Take the OP's question as stated, without the carping about how it could be achieved. Assume that God, or Alien Overlords, either "Will" it, or apply "tractor beams" to slow the rotation over a reasonably long time, to avoid the H.G. Wells effect (from a story in which the Earth stopped abruptly, but people and things shot forward at their previous speed). Assume that "stoppage of rotation" means that one meridian has High Noon without change, and another 180 degree opposite meridian has perpetual Midnight. The Earth makes one rotation per year. Assume the Sun always shines over the Prime Meridian in Greenwich, (so the Sun "never sets on the British Empire.") London would get very, very hot, and likely become uninhabitable, as would much of Europe.Places along the International Dateline at the Antimeridian would get very, very cold, likely become uninhabitable, and agriculture there would become very difficult. Lots of ocean creatures would die from it being too hot or cold. The ocean near antimeridian might become permanently frozen. There would be a "Happy Medium," or "Goldilocks Zone," perhaps a bit Sunward from the 90th meridians east and west, only a small fraction of the present zone where people flourish, where the temperature and insolation would be most advantageous. A large portion of the population would likely starve, burn, freeze, or die in conflict as people sought to migrate to the place where it was not too hot and where crops could be grown. Some extreme weather might occur, with massive storms due to the vast temperature differential. Edison (talk) 04:10, 26 August 2012 (UTC)
 * That's another star-deserving answer. One can posit the Earth slowing to no rotation relative to the sun due to long-term tidal slowing due to the moon.  Once the Earth became tidally-locked, the effect would be as Edison said.  See our article Aurelia and Blue Moon and the full free video, NGC Presents : Extraterrestrial. μηδείς (talk) 06:33, 26 August 2012 (UTC)
 * Edison, when you simply violate conservation of angular momentum, have you considered all the consequences? You've jumped straight in to analyzing how life will adjust to temperatures on a non-rotating planet, but you are assuming a lot of non-sequitors!  In this hypothetical universe when angular momentum may magically just "disappear," what will happen to, for example, chemical reaction kinetics?  Will life-forms still be able to metabolize glucose, now that we've obliterated fundamental rules about the way mass and inertia work?  Will atomic or molecular structure still be stable in a universe that may freely "cancel" angular momentum without cause?  Carping about how something happens is precisely what a scientific analysis is predicated on.  Without an assumption of consistent physical law, validated by consistent observed phenomena, it's absolutely impossible to predict outcomes.  Nimur (talk) 15:01, 26 August 2012 (UTC)

Why didn't the world enter a nuclear winter in the mid-20th Cent.?
Yes, this is two nuke-related questions in less than a week for me. I'm weird like that. Anyway...

These guys estimate that a "nuclear conflict ... with 100 Hiroshima-size weapons ... would significantly disrupt the global climate for at least a decade." By this chart's reckoning, 116 atomic bombs were detonated worldwide in 1958; 71 in 1961; 178 in 1962; and no less than fifty on a yearly basis from '63 through '80. However, according to this, there has been absolutely no measurable decrease in the amount of sunlight that reaches the earth's surface because of any nuclear detonation or series of detonations ever.

Is it just me or does all of this seem somewhat contradictory? Since most nuclear weapons are at least in the Hiroshima range (many of them larger by several orders of magnitude), and since we clearly had periods in the 20th century where well in excess of one hundred nuclear weapons were detonated within several months of each other, shouldn't we have seen some sort of effect on the weather, even a minor one, at some point between 1958 and 1980, given the estimate I initially quoted? Evanh2008 (talk&#124;contribs) 01:29, 25 August 2012 (UTC)


 * The climactic effects of nuclear weapons come from burning lots of stuff (cities, forests, what have you) — it's about releasing carbon dioxide into the atmosphere. Only two of the nuclear weapons in the 20th century were set off over areas with significant stuff to burn. The others were set off on remote atolls or islands, in deserts, in the very high atmosphere, or underground (the majority). A more interesting question to me would be whether there were any measurable effects from the amount of carbon put into the atmosphere during World War II, when there were systematic programs of city burning perpetuated by many of the participants. As for mass burning affecting climate change in general, one of the theorized explanations for the Little Ice Age is a decrease (because of rapid depopulation) of planned burns that had gone on for centuries in the New World. Just an interesting idea. --Mr.98 (talk) 01:37, 25 August 2012 (UTC)


 * It's not about carbon dioxide. See Nuclear winter. It's about soot and other particulates that get kicked up into the atmosphere. 203.27.72.5 (talk) 01:51, 25 August 2012 (UTC)
 * Well, right, other stuff as well. My point still stands... --Mr.98 (talk) 23:25, 25 August 2012 (UTC)
 * Some researchers have speculated that we may have had a "petit nuclear winter" in the second half of last century . 203.27.72.5 (talk) 02:17, 25 August 2012 (UTC)
 * Seems unlikely to have anything to do with testing, though. The amount of particulate matter added to the atmosphere by nuclear testing is but a drop in the ocean of human-added effluents in the late 20th century. The logic of that particular paper doesn't strike me as terribly compelling. --Mr.98 (talk) 23:25, 25 August 2012 (UTC)
 * I'm inclined to take that first source (claiming no effect) with something of a grain of salt; it was published in June 1957, prior to really large-scale atmospheric testing. (1956 had only 33 atmospheric tests, 1955 just 23; there were fewer than 20 per year between 1951 and 1955, and just 6 in total between the end of World War 2 and 1950.) Further, the publication was prepared by the Armed Forces Special Weapons Project of the Department of Defense&mdash;an agency that might have a certain interest in concluding that nuclear weapons use had fewer long-term hazardous effects. Even then, they acknowledge in the fine print that firestorms caused by large-scale conventional bombing had been known to affect weather; it seems to be splitting hairs to absolve the bomb for responsibility for the fires it starts.
 * When you look at the number of nuclear tests each year, you also need to consider where those tests occurred. (Take note of the terms of the various treaties described under Comprehensive Nuclear-Test-Ban Treaty.)  While there were more than fifty tests per year from 1963 through 1980, there were fifty or more aboveground (atmospheric) tests in just '57, '58, '61, and '62.  After 1963, there were never more than ten aboveground tests in any one year, and no such tests in most years.  Underground tests – while certainly problematic for an assortment of reasons – would not be expected to have any major effect on climate.  Tests that were conducted aboveground always took place in remote areas (deserts, oceans) where substantial fires would not be sustained by forests or buildings.
 * Finally, even if 1950s climate sensing and modelling technology failed to detect the effect of a few dozen explosions, one should not be sanguine about the effect of thousands of warheads (including large numbers of high-yield bombs) that could potentially be fired in a major nuclear exchange. TenOfAllTrades(talk) 04:40, 25 August 2012 (UTC)
 * Interestingly, there is a connection between climate change and nuclear weapons — but it's because many of the methods for making sense of climate change today originated in studying the dispersal of nuclear fallout. There was a good article on this recently in the Bulletin of the Atomic Scientists. (Incidentally, Samuel Glasstone was a very well-respected writer on the topic of nuclear weapons effects. Whatever he wrote then would have been accurate knowledge for its time. His Effects books — there are multiple editions — were government-produced works but they pulled no punches.) --Mr.98 (talk) 23:30, 25 August 2012 (UTC)


 * For real, measurable, global effects of nuclear testing, you may be interested in how bomb carbon factors in to carbon dating, as well as many other areas of Biogeochemistry. See e.g. SemanticMantis (talk) 06:25, 25 August 2012 (UTC)

How many calories in a shot of vodka?
How many calories are in one shot (1.5 fl oz) of 80 proof vodka? Googling seems to give a variety of answers, but does about 100 calories per shot seem reasonable? Thank you, 99.92.102.199 (talk) 04:22, 25 August 2012 (UTC)


 * This site says there are 97 calories in a shot of Smirnoff 80 proof. Evanh2008 (talk&#124;contribs) 04:27, 25 August 2012 (UTC)


 * This elegant website, http://nutritiondata.self.com gives excellent full nutritional data on all foods and beverages. It indicates 64 calories for one oz 80 proof. μηδείς (talk) 17:44, 25 August 2012 (UTC)


 * In Russia, vodka shoots you. Clarityfiend (talk) 21:36, 25 August 2012 (UTC)
 * Is that Yaakov Smirnov? μηδείς (talk) 02:10, 26 August 2012 (UTC)
 * Unless my subconscious is dredging up somebody's comedy routine, it's me. Or maybe it's the Smirnoff talking. Clarityfiend (talk) 04:48, 26 August 2012 (UTC)
 * That is definitely a take-off from a joke I have heard. μηδείς (talk) 05:01, 26 August 2012 (UTC) See http://avalon.power-rpg.com/t320-in-soviet-russia-jokes
 * I'm not taking credit for this subgenre of joke, only this particular instantiation (until somebody comes along and proves otherwise). Clarityfiend (talk) 07:15, 26 August 2012 (UTC)
 * Bad jokes cluttering the Ref Desk is one thing, must we pick them apart here as well? BigNate37(T) 07:27, 26 August 2012 (UTC)
 * See Russian Reversal. Sorry... :) Wnt (talk) 12:07, 27 August 2012 (UTC)


 * Note that one shot in most countries is 1.5 ounces, so your figure of 64 roughly agrees with the 97–100 figures above. See Shot glass. BigNate37(T) 07:27, 26 August 2012 (UTC)
 * Wow, this was mentioned in the question itself, my bad. When I start missing things that obvious, it's time for bed. BigNate37(T) 07:35, 26 August 2012 (UTC)

Kuiper belt object
Are those objects orbit around the sun or are they just flying around randomly?184.97.233.160 (talk) 05:08, 25 August 2012 (UTC)


 * The article indicates they're in orbit, e.g. one of its members, Pluto, is in a significantly elliptical orbit. ←Baseball Bugs What's up, Doc? carrots→ 05:20, 25 August 2012 (UTC)


 * Also note that "flying around randomly" isn't possible. Since "an object in motion stays in motion (at the same speed and direction) unless a force acts upon it", they would soon leave the solar system.  Therefore, they must be gravitationally bound to some object in the solar system, in this case, the Sun. StuRat (talk) 06:01, 25 August 2012 (UTC)


 * Good point. Tell me if I'm wrong about the following: My assumption about the Big Bang is that immediately afterward, things were pretty much "flying around randomly". Over time, they began to coalesce into various objects, like stars and planets and of course galaxies. Given the many billions of years since then, would it not be the case that there are far fewer objects "flying around randomly" than there might have been after the beginning? ←Baseball Bugs What's up, Doc? carrots→ 06:07, 25 August 2012 (UTC)


 * Actually, the process is poorly understood, and we don't have a good answer for what happened. We know two things: from the Cosmic microwave background radiation we know that the very young universe was homogeneous: that is, it was evenly distributed and looked uniform in all directions and at all scales.  The second thing we know is that it doesn't look like that today.  What happened in between, that is what happened to cause the universe to go from a state of homogeneity to one of heterogeneity (from looking like milk to looking like cottage cheese) isn't well understood.  This is explained at Structure formation. -- Jayron  32  06:15, 25 August 2012 (UTC)

"We know two things: from the Cosmic microwave background radiation we know that the very young universe was homogeneous: that is, it was evenly distributed and looked uniform in all directions and at all scales. The second thing we know is that it doesn't look like that today." actualy your post is partialy rong (at least if I have understood you correctly) because although the universe is not homogeneous at a small scale but it is homogenious at a large scale.

While it is tru that we do not know how the erly universe looked like the big bang article segests that there were far fewer objects "flying around randomly" just after the big bang than there are nau.Aliafroz1901 (talk) 10:32, 25 August 2012 (UTC)


 * What the universe looks like on a large scale is dependent on what the shape of the universe is, which is also something we don't know. If the universe is really infinite in extent, then yes, it is perfectly homogeneous on a large enough scale, because trivially any local unevenness "smooths out" when looked at from the perspective of infinity.  The problem is a) this isn't exactly the same as what I said above, because in the early universe it was homogeneous at all scales, not just if you back out to (near) infinity.  That is, under our current understanding of the early universe, it doesn't matter whether you look at it on the atomic scale, the human scale, the solar system scale, or the entire universe scale, it would all look homogeneous.  Today, the only scale that may work on (and again, it depends on what the universe really looks like, which we don't have a firm grasp on at that scale) is the "entire universe scale".  Today, the universe is decidedly heterogeneous on all other scales, rather self-evidently: I'm standing here, and I'm not standing over there.  There's star material in some places, and not in others.  There are atoms and molecules, and then there are places with empty space.  In the early universe, this wasn't true.  It was all a uniform matter/energy soup.  The mystery is how it got from that state to what we have now.  -- Jayron  32  14:20, 25 August 2012 (UTC)


 * That's not a mystery. Things gravitated together. The details may be complicated but we do basically know what happened. Biological evolution is very complicated but it would be misleading to say that there were only prokaryotes a few billion years ago and there are humans now and it's a mystery how that change happened. -- BenRG (talk) 21:52, 25 August 2012 (UTC)


 * On a very fuzzy level, we know that there were "perturbations" which caused local areas of higher density, which lead to a sort of gravitational positive feedback that led to objects coalessing out of the soup. Cosmological perturbation theory does a nice job of explaining what it would look like (though the current article looks like a technical glossary vomited all over it, and covered up any text which may be useful to the lay reader), but it still isn't well understood what the antecedants for the events that led to structure formation were.  There's a lot of handwaving going on that still needs to be resolved by physics.  -- Jayron  32  05:09, 26 August 2012 (UTC)
 * Why would there be things that could gravitate together? In a truly homogeneous universe, there is absolutely nothing different between here and there.  One of the greatest unanswered questions is where the present inhomogeneity originated from.  Was itnhomogeneity always present, but latent, in some kind of hidden-variable of an otherwise homogeneous soup?  Or was the early universe always inhomogeneous?  Nimur (talk) 15:12, 26 August 2012 (UTC)


 * COBE found fluctuations in the temperature of the cosmic microwave background in 1992, shown in this famous image. This was one of the most important experimental results in the history of modern cosmology and a key piece of evidence that big bang cosmology (as opposed to some steady-state cosmology) is actually correct and the CMB is a relic of the early universe. Inflation predicts fluctuations with a spectrum that matches what was seen by COBE (and later refined by WMAP). Both of you sound as though you've never heard of this. -- BenRG (talk) 05:37, 27 August 2012 (UTC)


 * A better solution than chastising us then is to fix the relevent Wikipedia articles. I can only report to readers here what I find when reading the relevent articles I link to, and if it says, as it does, at Structure formation, that this is a, and I quote, "largely unsolved" problem.  If what that is supposed to say is "well-understood and mostly figured out" than it shouldn't say "largely unsolved" then, n'est ce pas?  You could also, you know, take a crack at the 90% of the physics and cosmology articles whose text is entirely unreadable by anyone except a select few people, but that might also be asking too much.  -- Jayron  32  05:44, 27 August 2012 (UTC)
 * I'm familiar with the COBE spacecraft and its follow-on missions to map the cosmic background radiation. Of course I've seen the pictures, and it's trivial to recognize the obvious inhomogeneity in the experimental result.  But I have no shame in admitting my limitations: as I understand the theory, nothing yet explains this observation - at least, not in a way I understand.  This physics is sufficiently complicated that it was worth the 2006 Nobel prize.  BenRG stated: "inflation predicts fluctuations"... but this is not an obviously-true statement.  If his statement is, in fact, valid, then it's predicated on some very difficult theoretical work about inflation.  I'll second Jayron's request: please improve the relevant articles, and help us find the appropriate source material.  From what I read, the observations only result in more questions about early universe cosmology.  And, as I read efforts to explain initial condition, I see a lot of effort to dodge this question: was the very early universe inhomogeneous?  Nimur (talk) 16:47, 27 August 2012 (UTC)

Correct, and I never said you were fully rong-what I said was that you were partialy rong (which you mite not be of course).Aliafroz1901 (talk) 14:46, 25 August 2012 (UTC)


 * What I mean is are "ALL" the Kuiper belt objects are orbiting around the sun? What if some of them are too far away for the sun gravity or anything gravity to act upon them so aren't they just flying around randomly or just stand still? (I know they are, including the Solar system, also spinning around the galaxy too, in the big picture) Anyway they could flying around randomly in a smaller scale compare to galaxy scale. Just like Earth is orbiting the Sun but bigger scale, the Earth is also spinning around the Milky way galaxy.184.97.233.160 (talk) 08:03, 25 August 2012 (UTC)


 * Gravitation has an infinite range. Everything in the belt is under the influence of the sun's gravity. If they were standing still relative to the sun for an instant, they would still accelerate towards it and begin to move in it's direction. 203.27.72.5 (talk) 08:20, 25 August 2012 (UTC)


 * True, but at some distance objects will never complete an orbit during the life of the universe, so saying it is "in orbit" seems iffy. StuRat (talk) 08:32, 25 August 2012 (UTC)


 * The Kuiper Belt, and the Solar System itself, are defined as objects which are gravitational bound to the Sun. So, if some object is just "passing through" the Kuiper belt, fast enough to not fall into orbit, it isn't really a Kuiper Belt object (although it might be mistaken for one until it's motion is charted). StuRat (talk) 08:30, 25 August 2012 (UTC)


 * It is certainly possible to have objects passing through the solar system without being gravitationally bound to the sun (that is, without being in a closed orbit). They need to be moving quite fast, though. In fact, we can quite easily work out how fast. I will ignore any complications from interactions with planets or light pressure or any of that stuff, and just treat the situation as a simple 2-body problem. The thing that determines whether an object is in an open or closed orbit (ie. whether it can reach infinite distance or not) is its total energy, it's gravitational potential energy plus its kinetic energy. Note, gravitational potential energy is defined, for convenience, to be zero at infinity and to get more and more negative as you get closer to an object (this seems really weird, but you'll see why it is useful in a second). The total energy of an object will be the same at all points in its orbit (conversation of energy). If that total is positive, then that means the object will still have positive speed at infinite distance, so it is an open orbit. If the total is zero, then it will "come to rest at infinity", so it can reach infinity but only just. If the total is negative, then it would need to have negative kinetic energy at infinity, which can't happen, so the object can't reach infinity - this means it is a closed orbit.
 * So, to figure out how fast an object needs to be going to avoid being captured by the sun, we just need to calculate the (negative) potential energy at a particular distance and work out what velocity gives an equal (but positive) kinetic energy. Pluto is, on average, about 6 billion km from the sun, so let's use that as our example distance. Using the formula at gravitational potential energy, we get the potential energy (of a 1kg object - mass will cancel out when we calculate the speed, so it doesn't matter) to be 22 megajoules. If we convert that into a speed (using E=1/2 mv2), we get about 6.6 km/s. Pluto's average orbit speed is 4.7 km/s (average speed isn't quite the same as speed at average distance, but it is close enough) so we can see that it is easily in orbit around the Sun. An object at the same distance travelling about 40% faster would not be in orbit and would eventually escape. --Tango (talk) 13:20, 25 August 2012 (UTC)

So what happen for the objects that outside the belt or outside of the Solar system? Are they going to fly around randomly?184.97.225.6 (talk) 21:30, 25 August 2012 (UTC)


 * Hopefully you'll find the Hill sphere article informative. If a body's orbit falls entirely within the Sun's Hill sphere (take a note of the calculation in that article's talk page, and at Talk:Comet, for some estimates about the diameter of the Sun's Hill sphere; it's bigger than once thought - big enough to encompass the Oort cloud). For some body in the galaxy whose path doesn't fall entirely within the Sun's Hill sphere, you wouldn't say it orbited the Sun. It might be within the Hill sphere of another star (or star group, like Alpha Centauri), so you'd say it orbited that, and its path would follow an elliptical orbit around that system's barycentre.  But it might not be, so it would orbit the galaxy's barycentre, as the Sun does. The galaxy is mostly empty, so such an object could go a billion years without its orbit happening to take it close enough to something else - when it did, that could bend that nice mathematical ellipse a bit (but mostly not close enough for it to be captured in that something else's system).  Although all the stuff orbiting in the galaxy is chaotic (it's a colossal n-body problem) it's not random or arbitrary; for most such things orbiting the galaxy's barycentre, their orbits are of near-mathematical elliptical perfection, over very lengthy periods of time. -- Finlay McWalterჷTalk 23:43, 25 August 2012 (UTC)

Estuary
"pollutants including heavy metals, PCBs, radionuclides and hydrocarbons from sewage inputs". What is the PCBs in this context stands for?184.97.233.160 (talk) 08:04, 25 August 2012 (UTC)


 * Polychlorinated_biphenyl 109.144.167.204 (talk) 08:09, 25 August 2012 (UTC)

Vaporizer, cannibis
Is it true that a vaporizer will virtually eliminate any risk of lung cancer or other cancers related to smoking? And is it possible to use a vaporizer with tobacco? ScienceApe (talk) 15:48, 25 August 2012 (UTC)


 * Only if you don't inhale. ←Baseball Bugs What's up, Doc? carrots→ 16:04, 25 August 2012 (UTC)


 * Wikipedia has an article titled Vaporizer (cannabis) which has some information you may seek. I don't know of the use of tobacco in cannabis vaporizers, but the have recently hit the market Electronic cigarettes which may or may not be similar in construction and use.  -- Jayron  32  16:38, 25 August 2012 (UTC)


 * Unlike nicotine, cannabinol is a rather heavy molecule and not water-soluble. Vaporizers won't work at all well.  Cleaning marijuana of stems and seeds and steeping it in hot but not boiling melted butter before then cooking the mixture in brownies will totally avoid the lungs, but not fat or cholesterol. μηδείς (talk) 17:39, 25 August 2012 (UTC)


 * Assuming inhalers are possible for THC, it might reduce the risk, since presumably there would be less "tar", but inhaling any foreign substance into the lungs carries some risk. Also note that the THC itself may continue to cause other problems, such as memory loss.  StuRat (talk) 18:54, 25 August 2012 (UTC)

Note that the safety of vaporizers is being presumed - given the legal obstacles and recent nature of the advance, I doubt there have been large, careful, long-term studies. Remember that it takes only a small amount of a carcinogen to cause harm, and any new process of heating and other processing potentially could create one. It seems like a good bet that it's a good idea, but in biology only the actual data can give an answer. Wnt (talk) 20:15, 25 August 2012 (UTC)


 * Responding to Medeis - cannabis vaporizers do not rely on water solubility. I can't speak to their effect on health, but I do know that they are capable of delivering THC to the lungs. thx1138 (talk) 17:55, 27 August 2012 (UTC)


 * Yes, according to the article they heat the oils to near their flash points. μηδείς (talk) 18:18, 27 August 2012 (UTC)

Why do different air masses equilibriate slowly ?
When I open my refrigerator door to the open air, or an oven door, the air masses inside them equilibriate very quickly, generally within 15-30 minutes. Why does this not scale for large air masses in the atmosphere? 128.143.1.192 (talk) 23:00, 25 August 2012 (UTC)


 * Are you sure it doesn't scale ? That is, does 1000 times the volume take 1000 times as long to reach equilibrium ?


 * That 15-30 minutes is probably only that long because the solid components or contents of the oven or fridge continue to give off or absorb heat over that period. Similarly, heat is being added to the atmosphere from the Sun and ground/water, and removed by radiation into space, at all times, so never really reaches an equilibrium.


 * There are also differences in scale regarding what type of heat transfer occurs the most (radiation, convection, etc.). StuRat (talk) 23:11, 25 August 2012 (UTC)


 * Yes, there's wind and convection and so forth and yet a stationary front can take several days to become a shear line (when the sharp contrast ceases to exist and becomes more of a diffuse gradient). Why is it so slow? 128.143.1.192 (talk) 00:16, 26 August 2012 (UTC)


 * I would be quite surprised if such transfers scaled linearly (1000 times the volume takes 1000 times as long) due to the square-cube law (specifically surface-area-to-volume ratio effects). The amount of heat energy an air mass has scales with it's volume. 1000 times the volume of air means 1000 times the amount of heat energy which needs to be transferred to equilibration. However, the transfer itself only occurs on the interface between the two air masses. The interface and interface-related effects don't typically scale as the volume, but as the surface area. An airmass of the same shape but with 1000 times the volume would not have 1000 times the surface area, but only 100 times the surface area. Thus naively you would expect the heat transfer (if it proceeds by exactly the same process in the two cases) to take 1000/100 = 10 times as long for the larger air mass. Of course, the relevant surface area and interface effects aren't going to scale *exactly* 100 fold, and with the larger air mass there may be different effects (wind generation and Coriolis effects may come into play, etc.), but the square-cube law gives a good first-order approximation as to why a small mass cools faster than a large mass. -- 205.175.124.30 (talk) 01:35, 26 August 2012 (UTC)

Also, how good is the adiabatic approximation in the weather modelling of air mass interactions? 128.143.1.192 (talk) 23:01, 25 August 2012 (UTC)
 * Buoyancy driven flow is governed by the Richardson number. Robinh (talk) 01:28, 27 August 2012 (UTC)

DNA
Whats the significance of knowing that DNA is double helix? 203.112.82.2 (talk) 23:25, 25 August 2012 (UTC)


 * 1) It's rather critical to knowing how it replicates (it unzips and both halves then form a new complete strand).


 * 2) It's also critical to knowing how the genes are stored. StuRat (talk) 23:32, 25 August 2012 (UTC)


 * Actrually, neither of those necessitates the "double helix". If it just looked like a long ladder, it would still need to unzip to decode, and it would still replicate the same way.  The deal with the double helix is is that it is a very efficient means of storing the information. If you think about how a telephone cord used to look (back when people had corded phones in their house), it's coiled up. The fact that DNA is coiled (rather than straight) allows it to fit a longer chain into a tighter space, and that improves the amount of information you can fit onto it. There's limited space inside a nucleus of a cell, and the way that DNA is coiled greatly effects how much information you can cram into it. The tertiary structure of DNA (how the double helix itself is packed) is also very important in this regard. -- Jayron  32  00:50, 26 August 2012 (UTC)


 * There's a nice diagram of that here. Coils upon coils upon coils. --Mr.98 (talk) 01:29, 26 August 2012 (UTC)


 * (ec) There is a famous line at the end of the original Watson and Crick paper: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.". That was all they said about it at the time, but it was enough. Looie496 (talk) 00:51, 26 August 2012 (UTC)


 * Yes, but the base-pair organization doesn't have much to do with the double-helix structure. RNA, for example, doesn't form double helixes.  It forms Stem-loop structures.  The base-pair organization explains how DNA codes for gentic information, the double helix helps explain how DNA codes for so much information because it allows the DNA to fit more information bits into a much tighter space than a straight chain would.  -- Jayron  32  01:11, 26 August 2012 (UTC)


 * RNA doesn't form double helices? Hmm... that'll be a big disappointment to the double-stranded RNA viruses and other organisms and cellular functions that depend on dsRNA (which include stem-loop structures, which are - double helical!).  dsRNA tends to take on A-form double helical conformation.  -- Scray (talk) 02:30, 26 August 2012 (UTC)


 * Yeah, you're right. I'm an idiot.  Carry on.  -- Jayron  32  05:01, 26 August 2012 (UTC)


 * To be clear, every nucleic acid, DNA and RNA alike, replicates based on a double-helix structure. In the case of RNA transcription, the DNA strands are parted and one is replicated by forming a temporary DNA-RNA double helix structure.  In a sense, even the translation of proteins from RNA is based on the double helix, in the sense that tRNA base-pairs with the RNA on the ribosome.  The double helix is important for lining up the right nucleotides for replication, for checking for errors afterward, but also for maintaining relative inactivity of the sequence afterward - a simple double-stranded RNA won't act as a ribozyme because it's just a straight rod, at least at the small scale relevant to forming catalytic sites.  There are, of course, a great many little oddities that you could mention in regard to it - artificial nanoscale engineering of complex structures, sequence-specific reception of radio-frequency or terahertz signals, the ability of supercoiling to convert overall torsion of the structure into a separation of strands, or vice versa, the ability to nick the structure so that topoisomerase I can release said supercoiling, under control, the ability of PCNA and other proteins to clamp onto the strand and run it like a more or less smooth "string" through holes in a protein complex ... there must be thousands of specific relevant significances. Wnt (talk) 03:40, 26 August 2012 (UTC)


 * Now, that is a great answer... Well explained, Wnt. -- Jayron  32  05:01, 26 August 2012 (UTC)