Wikipedia:Reference desk/Archives/Science/2011 February 9

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February 9

What's a good nonpolar organic solvent?

Preferably not carcinogenic. --75.15.161.185 (talk) 00:26, 9 February 2011 (UTC)

Can you be a bit more specific about your needs? How about cyclohexane? TenOfAllTrades(talk) 00:53, 9 February 2011 (UTC)

It should be able to dissolve lipids but not other compounds in food. --75.15.161.185 (talk) 02:32, 9 February 2011 (UTC)

Lipids are basically the entire class of all hydrophobic biological compounds, so by definition if it dissolves substantially in cyclohexane, it is a lipid. I am pretty sure that's how lipids were classified in the earliest days when such things were classified. See Lipid for more. --Jayron32 03:57, 9 February 2011 (UTC)

Vegetable_oil#Extraction notes that hexane and supercritical carbon dioxide are used commercially to extract oils from the vegetable matter. (I assume that there's probably a food-grade hexane for that purpose.)-- 174.24.195.38 (talk) 04:10, 9 February 2011 (UTC)

Flight control surfaces on modern airliners

In modern airliners, how do the flight control surfaces work? I know that they are usually powered by hydraulics, but how is the power applied from the hydraulic system to the control surfaces? Is it a cable system, levers and hydraulic cylinders, etc.? Also, what does the mechanism inside the flap canoes/fairings look like and how do they work?67.169.5.125 (talk) 05:25, 9 February 2011 (UTC)

The engines drive hydraulic pumps through their accessory gearboxes. The control inputs by the pilots are interpreted by the flight control computers which in turn actuate various valves to move the relevant hydraulic rams attached to the control surfaces. Feedback from the surfaces is returned to the flight control computers which in turn move the controls to provide tactile feedback to the pilots. This is the short answer - for a more comprehensive answer, read Fly-by-wire. Roger (talk) 08:44, 9 February 2011 (UTC)

Homework question on momentum + pendulum

Hi all,

I have a physics homework that I am completely stuck on. I have no clue how to approach this question at all. Any help would be appreciated!

In a ballistic pendulum an object of mass m is fired with an initial speed v_0 at a pendulum bob. The bob has a mass M, which is suspended by a rod of length L and negligible mass. After the collision, the pendulum and object stick together and swing to a maximum angular displacement theta as shown . http://session.masteringphysics.com/problemAsset/1010989/28/1010989A.jpg

Find an expression for v_0, the initial speed of the fired object.

Again, any help would be appreciated!! —Preceding unsigned comment added by 169.232.78.43 (talk) 05:45, 9 February 2011 (UTC)

The calculations actually have two parts. When the bullet impacts the bob, kinetic energy is lost to friction, but momentum is concerved. When angle theta is reached and the bob is at rest, the remaining kinetic energy (which you can calculate from knowing what the momentum will be) has become gravitational potential energy. If you can write out the formulae for all of that, you can solve for V_o in terms of theta, L, m and M. Someguy1221 (talk) 05:56, 9 February 2011 (UTC)

Initially, I would tackle this problem using the principle of conservation of linear momentum. Momentum of object prior to impact equals momentum of object plus bob after impact.

Mechanical energy is not conserved during the collision because some of the initial energy of the object is converted to heat, and some is used in deformation of itself and the bob as it enters. Kinetic energy and potential energy can be calculated for the period after the collision. Mechanical energy is then conserved for the period from the end of the collision until the bob comes to rest, and that should yield your answer. Dolphin (t) 07:16, 10 February 2011 (UTC)

I have been thinking further about your question, and my answer immediately above. This is a difficult question for someone who is new to the concept of momentum. As Someguy1221 wrote The calculations actually have two parts. Before tackling your question, a student should be fully familiar with the first part, which is the sort of question that goes like this:

An object of mass m₁ moving at speed v₁ collides with a stationary object of mass m₂ and the two objects coalesce (stick together). What is the resultant speed v₂ of the coalesced object? (Use conservation of momentum).

When you are comfortable with this sort of question, try finding the initial kinetic energy of object m₁, and the final kinetic energy of the coalesced object. You will notice the former is greater than the latter. The difference is equal to the energy used in deforming the two objects as they collide and coalesce, plus some energy converted to heat and possibly also noise. Energy is conserved, but mechanical energy is not. Dolphin (t) 05:17, 11 February 2011 (UTC)

are

are concrete warehouses like bestbuy insulated i see none — Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 06:44, 9 February 2011 (UTC)

Punctuation would help us to understand your question. --Lgriot (talk) 08:34, 9 February 2011 (UTC)

There's lots of ways they could do it. Probably the simplest is a double wall with insulation in between like this: Insulated concrete form. Or you install metal studs inside the building and insulation between them, then drywall. Ariel. (talk) 08:46, 9 February 2011 (UTC)

If the universe is not spherical...

When something expands at the same rate from a single point, the result is a sphere. If something expands at different rates in different places, the final result is a non-spherical shape.

So, if the universe is flat, saddle-shaped or anything but a sphere, what mechanism explains this uneven distribution of expansion? Thanks. Leptictidium (mt) 07:35, 9 February 2011 (UTC)

If I'm reading you right, your question assumes that the universe expanded from a point into the nothingness around it. That's not the case. The universe would have always had its current overall topology, and has simply been getting bigger. Someguy1221 (talk) 08:29, 9 February 2011 (UTC)

So, assuming the universe is flat: the Universe wouldn't have expanded from a single point, as proposed by the Big Bang theory, but rather from a single, infinitely small, "sheet of paper"? Leptictidium (mt) 09:18, 9 February 2011 (UTC)

No, but I'm going to wait for someone with a better grasp of generaly relativity to really answer that, but in the meantime please treat yourself to metric expansion of space. Someguy1221 (talk) 09:25, 9 February 2011 (UTC)

If you insist on imagining that the universe expanded from a single point then you have to remember that this point is not embedded in some empty space. The point is the entire space, it is not embedded in anything. However, it is better to remember that the "Big Bang" is actually nothing but the result of an extrapolation of the observed expansion backwards in time, and in fact beyond the limits where our understanding of physics holds (which gets close to the BB but does not reach it). We do not know what the Big Bang looked like. --Wrongfilter (talk) 09:41, 9 February 2011 (UTC)

Indeed. The Big Bang theory does not assume that the Universe "expanded from a single point". It proposes that the Universe was originally in a very hot, dense state; it makes no assumptions about the topology of spacetime in this state. Also, Leptictidium, I think you have misunderstood the meaning of "flat" when applied to a four-dimensional manifold such as spacetime. You may learn more by reading our articles on the shape of the Universe and the flatness problem. Gandalf61 (talk) 09:57, 9 February 2011 (UTC)

Why would faster than light travel mean going back in time?

It's a point that I don't really understand. Yeah, sure, perhaps nothing can go faster than light, but I don't get the "going back in time" bit. If when I look at the Moon, I see it as it was about 1.5 seconds ago, then if I flash myself there instanteously, I would be there as it is right now, 1.5 seconds into the future of what I was seeing. What is paradoxical about that? When I am far away from a man chopping wood, I hear the axe hit the wood well after I see it strike. If I move next to him, then I see and hear the chop at the same time. If everyone was blind, and had to depend to sound only, would someone argue that if sound could travel instantaneosly, you could go back into time?

Also, while it has been observed and now measured very thoroughly, we know that everyone sees light travelling at the same speed regardless of their own local motion, or that of the object which is transmitting the light. But I don't think it has ever been shown why this is true, or has to be true. Is that right? Myles325a (talk) 11:07, 9 February 2011 (UTC)

To answer your first question - strictly speaking, the special theory of relativity does not forbid an object from travelling faster than the speed of light - it forbids an object from accelerating from a slower-than-light speed to a faster-than-light speed (or vice versa). This is because an object with a non-zero rest mass would have an infinite relativistic mass and hence infinite energy if it ever travalled at the speed of light. Photons side step this problem by having zero rest mass - but as a result they can only ever travel at the speed of light, and cannot speed up or slow down. Physicists have postulated hypothetical particles called tachyons that always travel faster than the speed of light. Although tachyons do not violate special relativity, they have some strange properties such as "imaginary" mass, and they also appear to violate the principle of causality, so most physicists do not believe they can exist in our universe. Gandalf61 (talk) 11:46, 9 February 2011 (UTC)

I've drawn some ASCII space-time diagrams in the early history of the internet, but can't seem to find them anymore. The problem is that if you go faster than the speed of light in one inertial system, you go back in time in another (relatively moving) inertial system. Take a look at Minkowski diagram, and in particular at Minkowski diagram#Constancy_of_the_speed_of_light and the following two sections. --Stephan Schulz (talk) 12:28, 9 February 2011 (UTC)

See also this article: Tachyonic antitelephone. So, if you can violate the speed of light limit by merely being able to send information faster than light (regardless of how you do it), then you can exploit this to build a device that is able to send information back into your own past. You can then build a "telephone" with which you can talk to yourself in the past. This then leads to a causal paradox because if you receice a phonecall now from your future self living tomorrow, you can then decide not to call past self tomorrow while, if you don't receive a phonecall, you can decide to call yourself. So, a clear paradox is obtained. Count Iblis (talk) 13:50, 9 February 2011 (UTC)

You say "you can decide", but this seems open to dispute. One assumes that a four-dimensional spacetime that in some region curves back on itself admits a mathematical solution, just as one which does not. Wnt (talk) 21:13, 9 February 2011 (UTC)

Light cone in 2D space plus a time dimension.

Let me explain using the light cone picture I've added. For any given point in space-time, the remainder of space-time can be divided into four zones called the absolute future (points that can be reached by traveling slower than light), the absolute past (points from which the current point can be reached by traveling slower than the speed of light), the absolute present (points lying directly on the light cone), and the absolute elsewhere (points lying outside both the future and past light cones). These zones are the same regardless of the velocity of the observer. If it is possible to send signals faster than the speed of light, then it is possible to send signals to points in the absolute elsewhere. In fact, by altering the velocity of the signal source, it is possible to send signals to any point in the absolute elsewhere. But if you pick a point in the absolute elsewhere and draws its light cone, you will see that the absolute elsewhere for that second point overlaps with the absolute past of the first point -- meaning that a return signal from the second point can end up in the past of the first point. The crucial point is that the only velocity-independent distinction between past and future is that given by the light cone. Within the absolute elsewhere, the distinction between past and future is a function of the velocity of the observer -- any particular point can lie either in the past or the future, depending on how the observer is moving. Looie496 (talk) 17:46, 9 February 2011 (UTC)

This assumes that the person can travel infinitely fast in any frame. However, it is possible that an ansible may allow infinitely fast transport in only one privileged frame at any given point in space, such as the frame of the cosmic microwave background or the aggregate mass of the universe. This frame presumably varies according to Hubble expansion, gravity and so on. In this way, an observer with some velocity relative to this absolute frame may see the ansible capable of transmitting into the past in one direction, but only into the future at a finite faster than light velocity in the opposite direction. But he never sees anything capable of transmitting into its own past. (this is akin to the one-way speed of light mind game) Wnt (talk) 22:22, 9 February 2011 (UTC)

Orbits and angular momentum

I love science but i'm not a scientist, so apologies if some of the terminology in this question is incorrect. Why do the planets orbit the sun on a single plane? Similar examples are planetary discs, or the stars within a galaxy - they all orbit on a plane as opposed to on a shell (think of the simplistic model of an electron 'shell' orbiting a nucleus). Is it something to do with angular momentum? —Preceding unsigned comment added by 80.168.88.74 (talk) 12:17, 9 February 2011 (UTC)

The article Formation and evolution of the Solar System and related Protoplanetary disk and nebular hypothesis explain quite a bit. In simplest terms (and I may get this a bit wrong, so actual physics people can correct me) is that as a cloud of debris rotates around a star, it forms a disk around the equator of the sun, the forces involved in the spinning encourge that shape. Since the planets all form out of the material of that disk, they retain that roughly planar orientation with each other. This is different from electrons "orbiting" a nucleus, because the electron cloud itself doesn't revolve around the nucleus. Also, so-called "spins" in electrons and in the nucleus of an atom is not actual physical "spinning", rather it is a property which obeys the mathematical rules of spinning; but it does not seem that electrons and nuclei actually rotate like a star or planet does. --Jayron32 13:06, 9 February 2011 (UTC)

Thank you Jayron. From the Formation article you linked to - "the competing forces of gravity, gas pressure, magnetic fields, and rotation caused the contracting nebula to flatten into a spinning protoplanetary disc". Could you explain how these forces cause the flattening? The spinning/flattening pizza dough in the article is a good analagy, it's just understanding how all these forces result in the net effect of flattening that I struggle to understand. —Preceding unsigned comment added by 80.168.88.74 (talk) 14:03, 9 February 2011 (UTC)

Very simple explanation: gravity wants $x=y=z=0$, but conservation of angular momentum prevents x and y from being 0 (except momentarily in the course of an orbit). Gravity gets its way in the third dimension, so the result is flat.

More detail: The angular momentum effect is quantified in the effective potential that prohibits having all the mass at the center (consider what happens in the last equation in that article when r is very small). Nothing prevents most of the mass from piling up at the center: that's the Sun. Moreover, the restriction only applies in the one plane perpendicular to the momentum; anything outside that plane returns to it at some point during its orbit, and it then has the opportunity to collide with other objects in the plane. Eventually almost all motion perpendicular to the plane is arrested and you get a disk. (I don't know the particular role that magnetism plays here.) --Tardis (talk) 16:45, 9 February 2011 (UTC)

The mathematics of the principal axes might be useful here. Without diving too deeply in to complicated mechanics treatment, it is a fact of physics that angular momentum must be conserved; and it is also a fact that in a lossy system (e.g., an n-body system with non-negligible gravitation between particles, and with collisions), even if rotational kinetic energy is initially distributed uniformly in the macroscopic system, inter-particle interactions will "leak" energy into the principle axes of the system. (You can accept this on faith, or you can work out the long-term evolution of the statistics of the equipartition theorem for an n-body gravitational system with collisions). It's not all that different from these nifty toys: tops that "only spin in one direction". The thing is, the system has conditions that allow energy to transfer from one mode of rotation (say, "aplanar" orbits with random alignments), towards a preferred, principle mode of rotation (planar orbits, aligned in the plane of the system's initial net angular momentum vector). Because of lossy system-instabilities, rotational energy concentrates into one mode. Nimur (talk) 22:55, 9 February 2011 (UTC)

Accretion disc is an interesting article about the subject. - manya (talk) 04:06, 10 February 2011 (UTC)

Aha! I've just had a eureka moment! I've been reading the articles you've all kindly linked to and they all helped. My understanding is that gravity and angular momentum are the two main forces. Gravity reduces the z axis to 0, whilst angular momentum prevents the x and y axis from being 0, the shape of which is a flat disc. This looks similar to Tardis' description, but it's taken all your responses to get me there, so thanks. —Preceding unsigned comment added by 80.168.88.74 (talk) 10:44, 10 February 2011 (UTC)

Straight line contrails

Why is it that nearly all vapour trails from aircraft show as a straight line? I have seen them expand as they get further from the plane but I would expect them to curve as the effects of cross winds move the vapour accross the sky.82.69.87.152 (talk) 12:56, 9 February 2011 (UTC)

The contrails do move with the wind. But that's no reason for them to curve. If the wind and the plane's course are both steady, you get straight contrails that extend from the current position of the plane in a direction that differs slightly from the plane's (ground-based) course. –Henning Makholm (talk) 13:23, 9 February 2011 (UTC)

Here's an illustration of Henning's point. The photo at the link shows the contrails left by an aircraft in a holding pattern, flying a 'racetrack' circuit over and over. While the plane always passes over the same track on the ground, the wind moves the contrails so that each loop of the pattern is offset slightly from the one before. TenOfAllTrades(talk) 14:19, 9 February 2011 (UTC)

Relative humidity also has a significant impact on contrail expansion or dispersion. ~AH1^(TCU) 22:39, 11 February 2011 (UTC)

is it a scientific fact that there is never a miscommunication between the tides and the moon that causes them?

Is it a scientific fact that there is never a miscommunication between the tides and the moon that causes them? 217.136.92.148 (talk) 13:07, 9 February 2011 (UTC)

First, you must define what you mean by "miscommunication". Otherwise, your question is nonsense. It is not possible to provide a reference for nonsense questions. Because this is not a chat room, we do not chat about nonsense. -- kainaw™ 13:16, 9 February 2011 (UTC)

The only possible way I can think of for the tides to not sync properly with the moon would be if there was a celestial body that had a gravitational influence on earth that was a significant percentage of the gravitational influence the moon had which was on the opposite side of the earth. In normal circumstances, the sun has the second greatest impact on the tides though it is too small to cancel out the lunar tidal impact in even the most extreme circumstances. This would mean that you would need something extremely large to pass by the earth at close range to cancel out the tidal force generated by the moon, and in that case, I would be far more worried about impacts to earth's orbit around the sun then a short term hiccough in the tidal cycle. Googlemeister (talk) 14:13, 9 February 2011 (UTC)

I suggest you read our article on tides and then come back here if there is something you don't understand.--Shantavira|^{feed me} 14:08, 9 February 2011 (UTC)

The original post is just trolling about the scientific illiteracy of Bill O'Reilly: [1]. TenOfAllTrades(talk) 14:12, 9 February 2011 (UTC)

You guys are not reading my question. I want to know if there's ever been a case of MISCOMMUNICATION - where the moon's gravity was not properly communicated, and the tides did not come in in response. I can put it to you this way: if gravitons are what transfer gravity, and gravitons are particles, has there ever been a case of a service interruption between the moon and Earth, so that these particles were dropped. Or, have they ALWAYS, come through, never a miscommunication? 217.136.92.148 (talk) 14:52, 9 February 2011 (UTC)

Only if you didn't pay your bill for gravitation service. You did remember to pay, didn't you? Acroterion _(talk) 15:00, 9 February 2011 (UTC)

Ha,ha, very funny. I've only been around since 1985, whereas there have been references to the moon and tides since at least the nineteenth century. 217.136.92.148 (talk) 15:02, 9 February 2011 (UTC)

There have been references to tides for as long as people have lived next to the sea and written about it. In seriousness, tides can be interrupted locally or otherwise affected by abnormal meteorological conditions, or, as we saw a few years ago, by earthquakes, neither of which have anything to do with the earth vs. Moon. Note that the sun makes tides too, accounting for spring tide and neap tide. Interruptions in gravity would be apparent by astronomical observation; so far as anybody knows, gravity has worked continuously since shortly after the Big Bang. Acroterion _(talk) 15:10, 9 February 2011 (UTC)

yeah I'm not asking about other disruptions in the tide, but about a miscommunication with the moon. I'm not interested in gravity everywhere, but the communication of gravity between the mean and the tides it causes. Scientifically, has there ever been a miscommunication? 217.136.92.148 (talk) 15:15, 9 February 2011 (UTC)

No there has not; neither can I think of a mechanism which would cause any such "miscommunication". Can we close the matter now? --Tagishsimon (talk) 15:18, 9 February 2011 (UTC)

You say "now" as though this answer has been given above: in fact, you are the first to reply to my question. (And then only at my repeated insistence). Now, this being the reference desk, would you have any way to tell me why you answer "no there has not"... How would we know if there had been a miscommunication at some point in the history of Earth and Moon? (If gravitons had been interrupted at some point, how would we know that.) Thanks. 217.136.92.148 (talk) 16:08, 9 February 2011 (UTC)

In fairness, I think most of the above posts were pointing in much the same direction. Still. I'm glad you accept that byou have an answer to your first question. As to your second question: I don't know. I tend to doubt there would be any forensic evidence we could latch onto. And I tend also to think that the firm expectation is that the laws of physics in this area are well enough proven that no-one is looking for the sort of "miscommunication" which I infer you to be asking about. You might want to read the Evidence of absence article to improve your grasp of this notion of "scientific fact". In my universe, there are hypotheses which have greater or lessor amounts of experimental or observational proof attached to them. These are what amount to "facts". And then there's a whole limitless cornucopia of stuff which is not proven or which cannot be proven, and which falls outside the "fact" category. Your "miscommunication" seems to fall into that bucket ... no one expects such miscommunication, no one is looking for it, there is no proof that it has not happened, but that says little or nothing about whether it has happened. Gravitational theory does not provide any mechanics for it happening. Astrophysics (admittedly to my very limited knowledge) has no examples of this sort of thing going on. On that basis, most of us are content to say "it's never happened & will not happen", but when coming up against a pedant, would add something like "to the limit of current scientific understanding". Does that help? --Tagishsimon (talk) 16:31, 9 February 2011 (UTC)

I think we can safely so that No, there has never been a case of the moon's gravity mysteriously not working. (If it ever did, I think tides would be the least of our worries, actually. It would presumably slip out of its orbit. If it ever happened to the earth-sun gravity we'd really be in trouble.) Tide tables can be calculated far in advance and on days with no wind they're usually spot on.

If gravity is caused by graviton particles, I suppose it's possible that a few of them might decay or otherwise go astray during the earth-moon trip. Perhaps that's what you're asking? But since gravitons aren't known to exist, this kind of speculation is less "theoretical physics" and more "making wild guesses about physics". In any case, that sort of "miscommunication" would be so infinitesimally small as to be completely unmeasurable. APL (talk) 15:23, 9 February 2011 (UTC)

I think the original question is probably based on some kind of bizarre misunderstanding, but it may be worth pointing out that the relationship between tides and moon is pretty complicated. Tides in any given location are generated by a combination of driving by the sun and moon, and the tidal resonance properties of nearby bodies of water. What you get, generally, is a complex oscillation that combines waves with lunar frequency, waves with solar frequency, and waves with local resonance frequencies. Large tides, such as those in the Bay of Fundy, occur when the resonance frequency is a close match to the lunar frequency. Looie496 (talk) 17:28, 9 February 2011 (UTC)

I vote "troll", and that's pretty rare for me. Comet Tuttle (talk) 17:34, 9 February 2011 (UTC)

As TenOfAllTrades already pointed out above, this is a rehash of Bill O'Reilly's brilliant proof of god (and I quote verbatim):"[Sun goes up, sun goes down,] tide comes in, tide goes out, never a miscommunication". What makes this ridiculous argument somewhat remarkable is that O'Reilly has been taped on numerous occasions saying those exact words, and given that "miscommunication" is not exactly an everyday word it makes him sound like he at first rehearsed the argument in front of a mirror or something until he had it down pat, ready to lash it out if the occasion demanded it. TomorrowTime (talk) 17:47, 9 February 2011 (UTC)

The possibility that there would be a "miscommunication" between the moon and the tides is exactly the same, scientifically, as the possibility that there could be a "miscommunication" between your body in the ground, so that you'd wake up hovering three feet above your bed. Scientists, understandably, will look at you slightly strange if you start seriously suggesting that in order to fly, all you have to do is forget to fall. They'll think you're "Looney Tunes". -- 174.24.195.38 (talk) 17:36, 9 February 2011 (UTC)

Why, has that ever happened? If not, I don't really get why you're bringing it up... 217.136.92.148 (talk) 18:11, 9 February 2011 (UTC)

The fact that it has never happened is exactly why the editor brought it up. thx1138 (talk) 19:50, 9 February 2011 (UTC)

It is a scientific fact that Newton's law of gravity (as adjusted by relativity) has never been reliably observed to fail either through lack of communication or for any other reason, either between a human body and the earth, or between the moon and the tides. We don't really get why you're bringing it up... Dbfirs 22:41, 9 February 2011 (UTC)

I'm bringing it up to verify Bill O'Reilly's premise (not his conclusion) about "never a miscommunication". I don't now about his conclusion, but from everything you all have written above, his premise is completely true and valid. Tide goes in, tide goes out, never a miscommunication. 109.128.101.244 (talk) 11:42, 10 February 2011 (UTC)

"Completely true and valid" in the same sense the statement "no one's ever been mauled by an invisible purple unicorn" is completely true and valid. People are raising issue with the "never a miscommunication" part because saying it implies that there is a chance for "miscommunication". Using the word "communication" brings in the concept of some sort of cosmic bureaucracy, where the moon sends out a memo to the ocean every morning about what time the tides should be ... and what would happen if it forgot to? Gravity doesn't work like that. No one would fault the statement "the tides rise and fall on a regular, defined, predictable schedule", but in the phrase "never a miscommunication" is an implicit premise which is faulty, and directly sets things up for his conclusion, that there must be a God to make sure all the appropriate paperwork gets filed every day. (See equivocation.) It's a bad conclusion, because it rests on a mistaken premise, that tides happen because of "communication". (Finally, everyone please note that saying an argument is invalid makes no statement on whether the conclusion of the argument is true or not.) -- 174.24.195.38 (talk) 17:38, 10 February 2011 (UTC)

The art, or rather the knack, to flying is not forgetting to fall, but throwing oneself at the ground and missing. --Tango (talk) 23:34, 9 February 2011 (UTC)

Correct Tango. I suppose missing would qualify as a miscommunication? Chipmunkdavis (talk) 12:06, 10 February 2011 (UTC)

So if your person attempting flight was to be entangled in barbed wire and not hit the ground, you could argue that he is indeed flying? Sounds more like hovering to me then actual flight. Googlemeister (talk) 14:20, 10 February 2011 (UTC)

The reason that these answers are getting so long and so off-track is the miscommunication inherent in using Miscommunication" the way OP does. Would he want to say that in on an overcast day the sun is Miscommunicating with the Earth"? I suppose you could put it that way, although no one ever does. Yes then, the Sun could "miscommunicate" with the Earth in that event, but gravity does not work the way photons do. It is only in some Sci Fi stories where you can shield an object from the force of gravity and thus make it weightless. Scientists do not consider gravity a 'force' in this way, they consider it to be part of the curvature of space.

That is why a sun can have a gravitational field for billions of years, and although it runs out of nuclear fuel, it does not run out of "gravitational fuel" as long as it retains its mass. So, no, the Moon's gravity cannot 'miscommunicate' with the 'Earth' any more than you can follow a path that curves left, and go left down it one day, and right another day. Myles325a (talk) 06:59, 11 February 2011 (UTC)

Is natural non-grey hair possible in old age?

Is it possible for this gentleman http://www.bbc.co.uk/news/world-europe-12404554 and other people of similar age to have naturally non-grey etc hair? Or must it be artificially dyed? I recall other politicians in continental europe also have youthful-looking hair. Now I think of it, bald politicians are very rare too. 92.24.185.155 (talk) 13:36, 9 February 2011 (UTC)

Fading of hair colour and loss of hair have a largely genetic component. Some of it is associated with the original hair colour (so blond hair tends to go grey faster than black hair, for example). My own grandfather had a full head of raven hair well into his 60s, while some people go bald or grey in their 20s. 86.164.25.178 (talk) 14:14, 9 February 2011 (UTC)

I know a woman who had dark hair into her 90s; I've not seen her for a few years, but as far as I know, she might still have dark hair. Nyttend (talk) 23:31, 9 February 2011 (UTC)

It is possible, but Berlusconi is a shallow, vain little man and had a hair transplant done. Also, I'm not sure why you got the impression that bald politicians are rare. TomorrowTime (talk) 09:18, 11 February 2011 (UTC)

Quality of 2011 transistor radio v. 1940s top of the range valve radio?

Would the sound quality that I get from a modern cheap transistor radio be better than that of the most de-luxe valve radio of say the 1940s? Allowing for the fact that 1940's AM radio may not have been so crowded or subject to noise as it is now. Thanks. 92.24.185.155 (talk) 14:11, 9 February 2011 (UTC)

For the sake of this hypothetical scenario, are both radios tuning in to the same radio transmission, or should we assume that you want to compare the quality of a 1940s broadcast to a 2011-era broadcast? Modern transistor radios can tune to FM, they can use "digital AM", and so on; so it's unfair to compare different types of transmissions that a 1940 tube radio could not demodulate in the first place. In terms only of noise quality and frequency fidelity between dc and 22 kHz, the best quality 1940s valve radios probably had equal performance to mediocre low-quality AM/FM asic integrated circuit tuner/demodulator/amplifier packages. And to be fair, "transistor radio" is a loosely used term: it historically referred only to those radios that used a single BJT for mixing (demodulating); but may also refer to a transistor power-amplifier, or to a modern fully integrated analog/digital mixed-signal system-on-chip radio and audio-amplifier package. If you want to be very precise, you'll have to specify what exactly you want a comparison between. Nimur (talk) 21:28, 9 February 2011 (UTC)

I don't know about technical sound quality, but I certainly prefer the sound output from a 1940s radio. I find cheap "trannies" annoyingly hissy and tinny, but this is probably a combination of poor reception, cross-channel interference and small loudspeakers. I've never heard a high quality transistor radio, but I expect it would sound better if I rigged up a large aerial to pick up a suitable signal. (Only long wave and satellite digital radio work properly where I live.) Dbfirs 22:32, 9 February 2011 (UTC)

Is that tinny-ness the effect of the radio or the speaker-cabinet? Cheap radios often do have poor low-frequency fidelity; often, a DC-blocking capacitor is added as a "high pass filter" to cut everything below, say, 200 Hz; but this is usually intentional because they are connected to miniature battery-powered speakers that couldn't reproduce those low frequency acoustics anyway. So we've got to compare apples to apples: the actual electrical output from a transistor tuner/amplifier is probably a higher-fidelity signal reconstruction of the original waveform. Post-processing (signal conditioning) can then be applied to make the device more suitable for portable/battery-operated speakers, at the expense of tone quality. Nimur (talk) 22:36, 9 February 2011 (UTC)

Yes, I'm sure you are correct about the circuitry, but for reception and sound output, I vote for the 1940s. There was considerable sound distortion in the decoding and amplifier circuitry in valve radios, but it was a very different distortion, and not nearly so annoying (or is it just that I got accustomed to it?) Dbfirs 22:52, 9 February 2011 (UTC)

Oh, it's a well-known fact among audiophiles that "exact, flawless, perfect recreation of input signal" is not pin-for-pin compatible with "pleasant-sounding." For example, an electric guitar effects-box intentionally adds noise to the signal (in various different ways, depending on the effect), because people like the way that distortion sounds. I happen to like the tone properties of valve amplifiers, myself; there are many aesthetic details of old technology that are very nice. And I still prefer the fades and fuzzes of AM radio, even though this "new-fangled" FM-technology can provide stereo sound. It's fun to hear WSM fuzz out when I'm driving past a mountain or a rainstorm, and there's no thrill like picking up the Nashville stations while I'm driving through West Texas. (Try doing that with an RDS-enabled side-channel stereo FM! Kids today, with their "technology...") But I can't objectively call it "better sound quality." Nimur (talk) 23:10, 9 February 2011 (UTC)

I've owned and listened to radios made in the 1920's, 1930's and 1940's. Not all 1940 radios were alike. Some were cheaply made with low output power, only a few tubes and a small cabinet, with a poor quality speaker. Those would be comparable to a modern very cheap and very small radio, which has wonderful signal processing combined with a tiny speaker enclosure which limits bass response and output volume. A premium 1940 radio would have a very large speaker in a large cabinet, engineered for fairly smooth frequency response, and with tone controls which could be adjusted for a limited frequency response for distant or noisy reception, or a wider response for a strong signal. Some radio programs in 1940 were studio presentations with a very low noise level and a good frequency response up to the high frequency limits applicable in the transmitter, to keep the signal within the allowed bandwidth. Premium radios were made to reproduce such broadcasts well. See [2] from 1938, which discusses "high fidelity" premium cost receivers selling for $200. In April 1940 you could buy a Stromberg FM receiver for $295 or less which would sound amazingly high fidelity, as in this ad. Such a receiver would put to shame most modern radios of low or moderate cost. After WW2, the state of the art had obviously advanced even farther. Here is a 1948 article about the quality of FM reception. The best modern radio would still outperform the best 1940's radio, by picking up FM stereo as well as through speaker and electronics advances, but a "cheap" modern radio would fall far short of a good 1940's radio. Edison (talk) 23:34, 9 February 2011 (UTC)

Fantastic links, Edison. "Even if you live next door to a man with an electric razor, your FM radio won't be bothered by it." I suppose I've been selling FM radio short!! Nimur (talk) 23:57, 9 February 2011 (UTC)

A good radio from the 1920's perfectly restored, required the tuning of two RF stages as well as adjustment of the filament voltage, to tune in a station. The sound came from a horn speaker, and was no better than the very cheapest small transistor radio. A late 1940's radio could sound very fine, indeed. Edison (talk) 05:29, 10 February 2011 (UTC)

Would the sound quality of an average radio in 2011 be better than that of an average 1940s radio? Would the sound quality of a large "stereo" 2011 radio with large speakers be better? I'm thinking of all the black and white American films from the 1940s, before people started watching television, where they play music on the radio. Ignoring the fact that its fiction, were they getting better, same, or worse sound quality than me? Thanks 92.29.122.239 (talk) 12:55, 10 February 2011 (UTC)

A 1940-era radio set probably received a band-limited AM mono- signal. (Though, it could have already been receiving FM, stereo, and wide band, those things were less common). The 1940 set probably used a nicer amplifier, loudspeaker, and cabinet, than you typically find in a run-of-the-mill FM set today. If you consider 8 kHz band-limited mono sound to be "poor quality", then the 1940 set would sound worse. If you consider today's tiny speakers a miniature resonating cabinets to be "poor quality" (enough to outweigh the stereo/wideband/noise), then the 1940 set would sound better. Take-away message: the two radios would usually sound different. In ideal, specially-constructed conditions, with certain broadcasts and certain receivers, it is plausible that the sound signal that finally comes out of the speaker might be exactly identical between a 1940 set and a 2011 set; all the necessary technology did exist in 1940 for low-noise, full-audio-spectrum, stereo, FM radio. Nimur (talk) 19:16, 10 February 2011 (UTC)

A late 1940's AM table radio in our house sounds better (more volume, more base, don't really notice the lack of high frequency response) than a 21st century somewhat smaller, typical bedside radio playing mono FM, stereo FM or AM. It just takes a few seconds to warm up. (Old adage: Transistors hiss, tubes hum.) A 21st century receiver with large speakers sounds far better than a good 1940's radio, with greater volume, less distortion, and wider frequency response. I doubt there was much stereo broadcasting in the 1940's. In the early 1950's before FM stereo, but after stereo tapes were available, one radio station I'm very familiar with did stereo simulcasting, with one channel on their AM transmitter and the other on their FM monophonic transmitter. Edison (talk) 06:16, 11 February 2011 (UTC)

On further review, a late 1940's moderate cost AM table radio would provide loud music in a 25 by 25 foot room. It takes about 10 seconds for the tubes to warm up and provide maximum output. There is a bit of audible hum, not at all disturbing, as well as some distortion, with a lack of extreme low frequency, and a lack of high frequency. It still fills the room better than a cheap 21st century AM radio, which is physically a small fraction of the size, with a much smaller speaker, and less output power. A premium 1948 radio/phonograph has sort of a thumpy bass response, maximized at around 100 Hertz, compared to better low bass response from modern high fidelity stereo systems. Edison (talk) 06:56, 13 February 2011 (UTC)

largest bird egg

Which bird which can fly lays the largest eggs? Googlemeister (talk) 14:45, 9 February 2011 (UTC)

If you allow mythical birds, then the roc would be a contender, (and the ostrich of course for living non-flying birds), but my guess would be a swan. Can anyone think of a larger? Dbfirs 16:23, 9 February 2011 (UTC)

Kori Bustard, Ardeotis kori is quite a bit larger than the swan. Roger (talk) 16:27, 9 February 2011 (UTC)

That's a much better answer. The Argentavis had an egg three times the weight of the swan egg (over a kilogram), but it is no longer around. Dbfirs 16:30, 9 February 2011 (UTC)

The Kori bustard is the heaviest flying bird today (I think), so, yes. But for egg size I might have to check. Crimsonraptor | (Contact me) Dumpster dive if you must 16:41, 9 February 2011 (UTC)

Andean condors have an egg weight of 280 grams or so, and the egg length is around 4 inches. So is that the record, then? Crimsonraptor | (Contact me) Dumpster dive if you must 16:44, 9 February 2011 (UTC)

The swan beats that with an egg weight of up to 340 grams, but I expect the Kori Bustard (paauw, Ardeotis Kori) egg is heavier, and the European Great Bustard ((Otis tarda) would also be a contender. Can anyone find a reference? The eggs of the Elephant Bird, or Vouron Patra (Aepyornis maximus) were the largest ever (bigger than any dinosaur egg), in fact they reached the physical limit of structural integrity for an egg-shape made of shell. Dbfirs 21:53, 9 February 2011 (UTC)

This reply to the condor claim was added after the reply below, but it is also a reply to Quetzalcoatlus claim. Dbfirs 22:17, 9 February 2011 (UTC)

Elephant bird. 92.29.122.239 (talk) 12:59, 10 February 2011 (UTC)

Elephant birds were flightless 92. Googlemeister (talk) 14:17, 10 February 2011 (UTC)

The eggs of Quetzalcoatlus must have been enormous. There has been an increasingly common recent suggestion that modern birds descended from dinosaurs. 2.97.217.143 (talk) 20:22, 9 February 2011 (UTC)

If by "increasingly common recent suggestion" you mean "we're as sure about it as we can be"... It's pretty much established and accepted that birds are descended from dinosaurs. --Jayron32 00:06, 10 February 2011 (UTC)

AFAIK, there weren't any flying dinosaurs, besides the early birds. --Sean 15:16, 10 February 2011 (UTC)

Actually, that's a possible no. It is possible that Rahonavis could be capable of flight (emphasis on possible, never confirmed). Crimsonraptor | (Contact me) Dumpster dive if you must 17:56, 10 February 2011 (UTC)

Well there were flying dinosaurs until about the mid 1980s when the word "dinosaur" finally got a rigid scientific definition, once and for all excluding the pterosaurs. APL (talk) 19:30, 10 February 2011 (UTC)

Thankfully. I get very snooty whenever I see Pteranodon or Dimetrodon, or even mammoths, labeled as dinosaurs. Crimsonraptor | (Contact me) Dumpster dive if you must 19:42, 10 February 2011 (UTC)

why is AIDS so hard to cure?

if it's just a virus, a bit of DNA, shouldn't it be really easy to cure instead of really hard? It's not like cancer, of which there are all these different types... it's just a piece of arguably not even living DNA... 217.136.92.148 (talk) 15:12, 9 February 2011 (UTC)

If you read the Article on HIV (AIDS is but an expression of HIV infection in its latter stages) you will see that this simple Virus is firstly attacking one of the vital parts involved in defeating "usual" viruses in the human body secondly has a high genetic variability (Theres all kinds of different kinds), making it very hard to attack by "conventional means". These two among many other things are making this "simple infection" such a challenge to science. The articles are really quite informative. --147.142.185.92 (talk) 15:19, 9 February 2011 (UTC)

Also, viral infections in general are much harder to cure than bacterial infections. See antiviral drug. In general, we only slow the virus down while the immune system adapts itself to do the actual curing. In the case of HIV, the immune system itself is attacked by the virus. --Stephan Schulz (talk) 15:47, 9 February 2011 (UTC)

Is it possible to use nanotechnology to do the actual curing instead? ScienceApe (talk) 17:20, 9 February 2011 (UTC)

If it were, AIDS would be cured already. --Sean 15:17, 10 February 2011 (UTC)

Err no. For example, we know stem cells can potentially regrow limbs, but we can't do that yet. In the future, it's possible to do so though. I was asking if we know if it's possible for nanotechnology to be used to cure viruses. ScienceApe (talk) 21:27, 10 February 2011 (UTC)

That's ridiculous. A virus is a piece of code, exactly the same as a binary executable on Windows, the sole difference being that instead of binary it's in quadrinary - you would need two bits to code each base pair. Now you're telling me that it's polymorphic. Fine. Does Norton etc. give up when a piece of code is polymorphic? No way. You're telling me, however, that we don't do any scanning of virus code whatsoever, in any way. We just slow down execution of it, so that the body's own antivirus can adapt to it! That's ridiculous. Imagine if all "Norton" did was run one very tight loop on all cores, and seek to random parts of the hard-drive, in an attempt to slow down the spread of the virus enough for Windows to catch up to it. That's ridiculous. Give me one good reason the human body couldn't have an artificial antivirus just like Windows can have a third-party one. The idea of having to use the body's immune system is just beyond comprehension for me. Why can't viruses be cured through artificial means -t hey're just a bit of code that, frankly, is not even alive. (Though this is in dispute.) 217.136.92.148 (talk) 16:25, 9 February 2011 (UTC)

Re-writing DNA codes is a very new science, and we cannot even cure the common cold yet. The difference between Norton anti-virus and curing AIDS is that there are millions of copies of the AIDS virus, and we can't (yet) get at all of them, especially in cells deep in the body, so we can't just remove that bit of code from all the infected cells. Dbfirs 16:40, 9 February 2011 (UTC)

If we contuinue to use the (frankly quite ridiculous) computer virus metaphor that the OP seens to have some understanding of: The problem with fighting HIV the way Norton's fights a computer virus is that if HIV was a computer virus the first thing it does when it runs is to delete the Norton's scanning executable. The human body is not a computer so the analogy is seriously limited. Roger (talk) 16:47, 9 February 2011 (UTC)

In addition to the immune system depression, one of the issues with HIV is that it's a retrovirus. That is, it actually incorporates it's DNA into the genome. All DNA looks the same, so once it's incorporated, there really isn't any difference chemically between HIV DNA and Human DNA. You can kill off the existing virus particles, and you might even kill off the cells which are producing virus proteins, but it is hypothesized that there are always "reservoir" cells which contain viral DNA, but aren't producing any viral proteins or RNA (until they are activated later). There's no way you can tell these reservoir cells from healthy cells unless you had a way to read and interpret the sequence of DNA, and we don't currently have ways of doing that, at least while the DNA is still in the cell. All the drugs and treatments we currently have either work on the protein or RNA level, or they attack all DNA indiscriminately, regardless of sequence. Programs like Norton Antivirus work because they have tools which can read the file sequences and compare those to viral signatures. We don't have anything like that for reading and comparing DNA sequences in the body. We have to rely on the natural decoding ability of the ribosome, or the cell's own DNA binding proteins to do sequence recognition. There's hopes that we'll eventually be able to do genome editing with zinc finger nucleases, designed homing endonucleases, or even sequence specific small molecule binders, but we don't have any of those yet. -- 174.24.195.38 (talk) 17:24, 9 February 2011 (UTC)

Actually, we don't know how to cure a single viral disease. We can immunize viral diseases and offer supportive care, and boost the bodies natural defenses but humanity has yet to actually cure viral diseases like we can some bacterial infections. Googlemeister (talk) 17:48, 9 February 2011 (UTC)

Thanks for that informative answer, which means you got my metaphor, unlike the person above you who thought I wanted the antivirus to run on the body's own immune system. So, you say we can't edit DNA in cells. But tell me this: if we could edit DNA in cells, then we could neutralize HIV in 1 cell or 2, or 10, 100, 1000, whatever. In fact, how many cells would have the HIV dna in a real case? Millions? Billions? I remember that there are between 10 and 100 trillion cells in the human body, depending on who you ask. How many of those would have hiv dna in them, in an infected patient? Which kinds of cells would have that DNA? Would cells, like bone cells, or brain neuron cells, have that DNA, which are totally impractical to replace? Or, on the contrary, would all the cells that have that DNA be of a kind that, in theory, you could replace... Thanks. 217.136.92.148 (talk) 18:18, 9 February 2011 (UTC)

There may be an answer,^[3] but developing it means perfecting the most terrible, insidious, and versatile weapon of assassination, mass destruction, genocide, and Orwellian surveillance ever conceived by the hand of man. Then again, the U.S. Army is beginning work on that anyway.^[4] Wnt (talk) 18:58, 9 February 2011 (UTC)

You hit on the real problem of DNA editing - even if we had an agent that could modify the DNA, how could you get it into all the cells that need it? We don't know. Probably the best bet is to use some viral delivery system - for HIV we could possibly use a (neutralized) HIV particle to deliver it, but infection is stochastic, so you couldn't guarantee that all cells would be hit. HIV infects primarily immune cells, so it would only be those cells which HIV infects which would carry the integrated viral DNA. Your brain cells probably would be unaffected, although while we think the viral reservoir cells are immune cells, we haven't identified them yet, so we can't be sure. Finally while killing the cell that contains it is one way to get rid of the foreign DNA, another possibility would be to "reverse" the integration process, cutting out the viral DNA and pasting the ends of the host DNA back together. As you might expect, that is much harder than just recognizing the DNA and killing the cell. - DNA editing is in the early research stages, and we can't tell yet if it would actually work to cure any disease. -- 174.24.195.38 (talk) 17:14, 10 February 2011 (UTC)

The common cold is "just" a virus, and we can't even cure that. thx1138 (talk) 19:46, 9 February 2011 (UTC)

The computer virus analogy breaks down on several important levels. First and most importantly: computer code can be stopped, it can be forced to cease execution then operated on discreetly and perfectly. You can't put the human body into a stable 'non-executing code' state, read it, scan it and arbitrarily edit the 'code'. Also key is the fact there's no way to stop the DNA from "executing" short of stopping biological processes entirely, not even killing the patient would do that. Secondly, there's no way to freely, arbitrarily and discreetly remove sections of DNA from a larger strand on-the-fly in vivo, if you could do that AIDS would be an utterly trivial problem yes, but so would death itself. 65.29.47.55 (talk) 01:17, 10 February 2011 (UTC)

Could you explain why "death itself" would become a trivial problem if we could do that? 109.128.101.244 (talk) 11:45, 10 February 2011 (UTC)

Death would become trivial, because if you can arbitrarily compare DNA to an exemplar sample (like you would have to, to find viral samples) and edit DNA however you want then it would be trivial not only to lengthen telomeres and also correct DNA degradation from environmental damage (incidental radiation, free radicals, copying errors, ect). The end result would be no age-related degradation of telomeres, which is thought to be a major factor in aging, while also getting around the problem normally seen with telomere lengthening: creating cancerous cells. 65.29.47.55 (talk) 08:10, 11 February 2011 (UTC)

A mechanic was removing a cylinder-head from the motor of a Dodge SRT-4 when he spotted a well-known cardiologist in his shop. The cardiologist was there waiting for the service manager to come take a look at his car when the mechanic shouted across the garage "Hey Doc, want to take a look at this?". The cardiologist, a bit surprised, walked over to where the mechanic was working on the SRT. The mechanic straightened up, wiped his hands on a rag and asked, "So Doc, look at this engine. I open its heart, take the valves out, repair any damage, and then put them back in, and when I finish, it works just like new. So how can I make 39,675 a year, a pretty small salary, and you get the really big bucks, $1,695,759, when you and I are doing basically the same work?". The cardiologist paused, smiled and leaned over, then whispered to the mechanic, "Try doing it with the engine running." - manya (talk) 03:50, 10 February 2011 (UTC)

See also SuperAIDS, viral evolution and blood-brain barrier. ~AH1^(TCU) 22:36, 11 February 2011 (UTC)

high protein consumption and kidney damage in humans

In humans, what is the correlation and regression curve between kidney damage and the consumption of high levels of protein (200 to 600 grams per day) to meet the basal metabolic rate (BMR)? --Inning (talk) 16:28, 9 February 2011 (UTC)

Please excuse me if I'm wrong, but that has the look of a homework problem. Looie496 (talk) 18:44, 9 February 2011 (UTC)

LOL... was just trying to phrase it so no one would say "We can't give medical advice." Next time just say you need to cover your ass since you do not know the answer to the question. --Inning (talk) 01:14, 10 February 2011 (UTC)

Well, now I'm confused. Do you need some kind of data plot, or do you just want to know how protein-focused a diet needs to be in order to cause kidney damage? Looie496 (talk) 05:02, 10 February 2011 (UTC)

Renal protein reabsorption? ~AH1^(TCU) 22:34, 11 February 2011 (UTC)

Dirty talk

I have two questions on dirty talk - 1. Psychology of dirty talk, 2. Evolutionary origin of dirty talk.

1. What is the psychology behind dirty talk?

2. According to the article Origin of language, "The development of fully modern behavior in H. sapiens, not shared by H. neanderthalensis or any other variety of Homo, is dated to some 70,000 to 50,000 years ago. The development of more sophisticated tools, for the first time constructed out of more than one material (e.g. bone or antler) and sortable into different categories of function (such as projectile points, engraving tools, knife blades, and drilling and piercing tools) are often taken as proof for the presence of fully developed language". So, how did Homo sapiens did dirty talk before the advent of language? What is the evolutionary origin of dirty talk? --Dolyop (talk) 16:31, 9 February 2011 (UTC)

1. It turns some people on to speak it, it turns some people on to hear it. When those people get together, everyone is happy.

2. There's really no way to know for certain since spoken language (or proto-language) can't fossilize, but giving signals of sexual availability is an extremely ancient and very basic form of communication among animals. Talking dirty would be part of that continuum, so even if we had a time machine it would be tough to draw a line somewhere. Matt Deres (talk) 18:35, 9 February 2011 (UTC)

Teleporting particles

According to the Heisenberg Uncertainty Principle, and Quantum Tunneling, particles like protons and electrons are essentially disappearing from reality and reappearing in reality in a different position. Would it be fair to say that these particles are essentially teleporting? Do neutrons also exhibit this behavior? ScienceApe (talk) 18:55, 9 February 2011 (UTC)

In quantum mechanics there is no underlying "reality" in which every particle has a definite location at every moment. If you drop the concept of "reality", I think you'll find that there is no way even to ask your question. Looie496 (talk) 19:21, 9 February 2011 (UTC)

I think if you drop the concept of "reality", there is no way to even ask any question. 109.128.101.244 (talk) 19:49, 9 February 2011 (UTC)

This usage of "teleporting" would be more confusing than enlightening. In almost every single atom (excepting hydrogen and helium) there are "nodes" where the probability of finding an electron by experiment drops to zero. Do all these electrons "teleport" when they cross these nodes? In your case, you might suppose that the particle doesn't exist inside a barrier of finite width, but in truth the quantum amplitude does penetrate the barrier (see figure in quantum tunneling). It is only that classically, the particle doesn't have the energy to be there. Wnt (talk) 20:35, 9 February 2011 (UTC)

I think there's no conundrum if you recognize that the wave function isn't the particle. The wave function is only a theoretical description that models certain aspects of the particle's behavior. "Where is the particle" is not word-for-word interchangeable with "where is the value of $|\Psi ^{2}|$ nonzero." The conceptual paradox of "teleporting" across energy barriers is only a problem if you try to equate "particle position" and "wavefunction" in a classical sense. Nimur (talk) 21:33, 9 February 2011 (UTC)

This would be less confusing if they simply weren't called particles. If they were called waves, the uncertainty principle and tunneling wouldn't be so surprising, because they also show up in classical wave theories. This page (which I found with a five-second Google search and haven't carefully examined) describes the classical frequency-time uncertainty principle for sound waves. An example of classical tunneling is the leakage of light between two fiber-optic cables separated by a small amount of air, even when the light is totally internally reflected. This is called evanescent wave coupling or frustrated total internal reflection, but it might as well be called tunneling (or the quantum version might as well be called evanescent coupling). Quantum mechanics is a unification of classical wave and classical particle theories. The unification is new, but practically every quantum phenomenon shows up in one or the other type of classical theory. The wave phenomena are the ones that are usually called "weird", but that's an arbitrary judgment. -- BenRG (talk) 04:53, 10 February 2011 (UTC)

Other phases of ice at room temperature

At room temperature, ice I will melt. Will any of the other forms of ice not melt at room temperature (as diamond does not)? 128.223.222.68 (talk) 19:51, 9 February 2011 (UTC)

What do you mean by "other forms of ice"? Water has a melting point of 0 °C (at sea level). Diamonds are made of carbon, which has a melting point of 3500 °C. thx1138 (talk) 19:54, 9 February 2011 (UTC)

http://en.wikipedia.org/wiki/Ice#Phases may be usefull to you 83.134.177.191 (talk) 20:12, 9 February 2011 (UTC)

According to our article, Ice_VII can remain solid at high temperatures. Also "...ice VII has the largest stability field of all of the molecular phases of ice"... Vonnegut's 'ice 9' notwithstanding. SemanticMantis (talk) 20:23, 9 February 2011 (UTC)

Of course, to have Ice VII, you would need to have a means to exert 10 gigapascals of pressure. Googlemeister (talk) 20:55, 9 February 2011 (UTC)

There is also the FICTIONAL Ice-nine. Dauto (talk) 23:28, 9 February 2011 (UTC)

I interpret this question as asking what solid materials would melt at room temperature (using "ice" in a looser sense as a crystal solid of some type). The answer is of course anything that's liquid at room temperature will melt at room temperature if you take a solid block of it out of the freezer. Mercury (element), for example, as in this video. Pure "Glacial" Acetic Acid's melting point is just below room temperature (16 C/62 F), and will indeed melt if brought into a warm room in a frozen state. It actually looks pretty similar to water ice: [5] Perhaps 128.223 needs to clarify their question. Buddy431 (talk) 00:00, 10 February 2011 (UTC)

I thought the question was clear. It is asking, if you start with water and apply suitable pressure and temperature to convert it to a different phase (such as ice VII), is it possible to achieve a phase that will remain solid at room temperature and (I presume this was intended) ordinary pressure? (Just as you might convert graphite to diamond and the diamond remains stable.) As I understand it the answer is no; water phases like ice VII will not remain stable when the pressure is removed. --Anonymous, 06:10 UTC, February 10, 2011.

Sodium acetate (hydrated) is often called "hot ice", and also consider the properties of supercooled liquid. ~AH1^(TCU) 22:32, 11 February 2011 (UTC)

Natural hazards and natural disasters humid continental climate

Which natural hazards and natural disasters are associated with Humid continental climate? —Preceding unsigned comment added by 65.95.106.36 (talk) 20:29, 9 February 2011 (UTC)

Since this has the look of a homework question, I'll respond by suggesting that you look at our article on humid continental climate and ask yourself what bad things can happen in the places it shows. The fact that you live in one of them should be helpful. Looie496 (talk) 20:50, 9 February 2011 (UTC)

Consider also the prevailing winds, ocean currents and any exposure to tornadoes, tropical cyclones and other weather disasters. ~AH1^(TCU) 22:30, 11 February 2011 (UTC)

Metabolism of alcohol

I am trying to figure out how the body is able to get so much caloric value from ethanol. the way that I understand it is that the body absords it directly into the blood stream unchanged. Alcohol is then converted to acetaldehyde by alcohol dehydrogenase. From there is it further metabolized to acetate and then to CO2 and water. Most of the alcohol is methabolized in the liver, and I have read that some of the metabolic conversons are very exothermic. How does the liver make use of these exothermic reactions to give alcohol so many dietary calories per gram?--160.36.38.218 (talk) 20:36, 9 February 2011 (UTC)

I think you're missing the most important step. As our ethanol metabolism article explains, acetic acid is metabolized to acetyl-CoA, which can be used as an energy source in many parts of the body via the citric acid cycle. Looie496 (talk) 20:57, 9 February 2011 (UTC)

So it is this step that makes it 1/3 better store of energy than sugar?--69.245.43.176 (talk) 21:41, 9 February 2011 (UTC)

I haven't checked your number with the biochemistry, but it seems plausible. High calorie fats or fossil fuels are typically -(CH2)- repeatedly with no oxygen added. Ethanol is CH3CH2OH - one oxygen per two carbons. Sugars are generally -(CHOH)- over and over, in other words, there is already one oxygen combined with each carbon. Now two oxygens per carbon is CO2. So you can think of ethanol as being (very roughly) gasoline that is 1/4 burnt, and sugar as gasoline 1/2 burnt; take (3/4 left) / (1/2 left) and you have your 3:2 ratio. (I omit in this that ethanol has an extra H2 at the ends, because it is short, and that fats sometimes omit H2s when unsaturated, etc. - to do this precisely you have to go through glycolysis, the Krebs cycle, oxidative phosphorylation and related processes in painstaking detail, and it turns out that you often won't get one single certain number even if you do!) Wnt (talk) 22:38, 9 February 2011 (UT

If you look at the energy budget of metabolizing glucose through glycolysis and oxidative phosphorylation, you see that only 2 ATPs are produced per molecule of glucose in glycolysis, but 30-36 ATPs are produced by the oxydative phosphorylation of the two acetyl-CoAs that are formed per glucose molecule and the NADH formed during glycolysis. One molecule of ethanol is turned into one of acetyl-CoA, and the alcohol dehydrogenase and aldehyde dehydrogenase create enough NADH to balance those formed by glycolysis. Two ethanol molecules thus only lose 2 out of 32-38 ATPs that are formed from one molecule of glucose. Because they are lighter than one glucose molecule, the calories per gram figure works out to be about the same (if not a bit higher for ethanol). -- 140.142.20.229 (talk) 23:05, 9 February 2011 (UTC)

FWIW, ethanol has molecular weight 46.07, and glucose 180.16, according to their articles. Thus glucose weighs 1.96 times more than two ethanols. (those oxygens are heavy) I didn't take that extra weight into account with my simple calculation, and yours would seem to indicate 100% more energy - either ethanol is using up some extra energy somewhere in processing, or the original poster is off, or we're both off, by about 50%. Sloppy science. ;) Wnt (talk) 18:06, 10 February 2011 (UTC)

Hmmm, according to food energy the actual values are 29 or 30 kJ/g for ethanol and 17 kJ/g for most carbohydrates (polyols) (74% more energy in ethanol). Wnt (talk) 18:11, 10 February 2011 (UTC)

Largest phytosaur

I've been doing a bit of research for an illustration I'm making, which has a large phytosaur in it. In fact, quite large. This page from the UCMP website states the largest grew up to 12 metres (39 ft), which nails my illustration, but doesn't give the species. Could anyone here help, because most of our articles don't give a size estimate? Thanks! Crimsonraptor | (Contact me) Dumpster dive if you must 22:35, 9 February 2011 (UTC)

Looks like that would be Smilosuchus [6] 75.41.110.200 (talk) 15:04, 10 February 2011 (UTC)

Thanks. I don't normally trust forums, but it looks like that'll be the best we can get. Crimsonraptor | (Contact me) Dumpster dive if you must 17:57, 10 February 2011 (UTC)

Why does snow melt on cold days?

I've always been puzzled that snow melts on sunny days when the temperature is below freezing. It's 13°F today, how is the sun making the snow melt? --68.102.163.104 (talk) 23:00, 9 February 2011 (UTC)

When snow is in direct sunlight, it can melt even when the air temperature is lower than freezing. --T H F S W (T · C · E) 23:01, 9 February 2011 (UTC)

Agreed, sunlight can raise the temperature of snow or ice several degrees. Sunlight can also reflect off a building and increase the intensity on the snow. If the snow is on the sidewalk or street, the dark color of the concrete or asphalt may cause it to heat up above the freezing point. If ice melter or road salt has been spread, that greatly lowers the melting point of the snow or ice and causes it to liquify and thus hastens its evaporation. Sublimation can take snow directly from its solid form to vapor form. Edison (talk) 23:21, 9 February 2011 (UTC)

A similar effect can be seen in Auto-defrost freezers (pretty much every freezer on the market these days), even thought the temperature IN the freezer never goes above freezing, the freezer creates conditions (mainly by circulating dry air) where unsealed ice cube trays will eventually sublimate away to nothing. Vespine (talk) 23:33, 9 February 2011 (UTC)

Where should post this? I am NOT happy with the physics sections of wikipedia.

Wikipedia needs a lock down on its basic definitions of physics after a thorough review by PhD professionals.

The articles are MISLEADING and students interested in physics are getting bad advice.

I am re-interested in physics and science after studying it many years ago and see many errors between my degree level textbook and basic definitions that are in Wikipedia.

For example the "conservation of mass" article starts to fall apart on the second paragraph, and the reader is left with the impression of a vague law that doesn't really work. There is a huge tendency to lump in classical, special relativity and quantum theory all in the same article which is really confusing to the layman ESPECIALLY when it is in the SECOND paragraph.

Also check out the opening paragraph of "energy", nice examples ? easy to understand? — Preceding unsigned comment added by 92.17.89.69 (talk • contribs)

The physics wikiproject would be better than here, but please remember that we are all volunteers and that if you find something unsatisfactory, the simplest thing to do is to fix it yourself. If you get stuck on something I'm sure there are plenty of people who can help you. SmartSE (talk) 23:14, 9 February 2011 (UTC)

I will also point out that Wikipedia seeks to be an encyclopedia. As such, it is not a replacement for a physics textbook or a physics class. Are you looking for a physics textbook? We can recommend numerous different authors, subjects, and depth-levels, depending on your need. Nimur (talk) 23:19, 9 February 2011 (UTC)

You should write a letter to their offices and request a refund, citing your dissatisfaction. You could also leave a negative review of the encyclopedia on Amazon, to discourage others from buying it. In the meantime, you should go to their competition, Britannica. 109.128.101.244 (talk) 23:28, 9 February 2011 (UTC)

Please don't bite the newcomers. Nimur (talk) 00:09, 10 February 2011 (UTC)

If you'd like to improve the article, please do — anyone, even you, can improve any article on Wikipedia. Comet Tuttle (talk) 23:39, 9 February 2011 (UTC)

It is our policy for the introduction (or lede) of an article to summarise the whole article. That means the introduction to the article on conservation of mass does need to cover classical mechanics as well as relativistic mechanics, so they are both important enough topics to be covered in the article. --Tango (talk) 00:13, 10 February 2011 (UTC)

Yeah, Tango, but the OP still has a point. Just because the lede has to summarize the whole article doesn't mean that it can't do so in a way that is easy to read and understand. The physics and other technical artilcles at Wikipedia are basically impenetrable for anyone without advanced training; which is kinda silly since the articles are often written so that the only people who can understand the article are people who don't actually need to read it because they already understand the concepts being discussed! I fully understand the OP's frustration because I share that frustration. Take a look at Magnetization for example. Lets say you were an English major in college, but still want to know a bit more how magnetization works. That article does you no good. Which is not to say that the techinical detail could not also be in those articles. It absolutely should be. Its just that there needs to be more attention given towards explaining concepts like conservation of mass and magnetization to people who may actually want to learn something from the articles. --Jayron32 01:02, 10 February 2011 (UTC)

I agree. I think wikipedia has a few excellent physics articles, true, but it also has many that are not directed to the general public and if the reader doesn't already understand the topic, he is unlikely to learn anything new. Dauto (talk) 02:29, 10 February 2011 (UTC)

As your hypothetical English-major-ish kind of person, I definitely agree with that Magnetization has problems. I didn't see why it needed the equation to be in the second line, or even to introduce the abbreviations M and V at that point. It would benefit from a simple change to: "In physics magnetization is...". This is a pure guess, but is magnetization actually how magnetic a piece of steel is? I.e. if I acquire a magnet and then leave it alone for a long time, it will become less magnetic. Itsmejudith (talk) 13:11, 10 February 2011 (UTC)

Per the recommendation, I have refactored the leading paragraph. Please feel free to improve the article further. Nimur (talk) 18:42, 10 February 2011 (UTC)

I've continued your work. In particular, I've moved the equation and technical definition to a new section. There is really no need for that much precision in the lede. I've also played around with the wording of what was left in the lede a little (there is still plenty of room for improvement, though). --Tango (talk) 19:01, 10 February 2011 (UTC)

Conservation of mass delves into the history of science, but doesn't do it well. Some is unsourced, other sources may be primary. There is a great leap from the 18th century to relativity, and the relativity is introduced simply by references to main articles. Itsmejudith (talk) 13:18, 10 February 2011 (UTC)

Wikipedia is ONLY for the casual whatever-ist and as such it should be compiled as if it were for a highschool freshman not a college grad. If the authors edited with this in mind, I think many more people would find Wikipedia useful. —Preceding unsigned comment added by 165.212.189.187 (talk) 14:14, 10 February 2011 (UTC)

"A lock down on its basic definitions of physics after a thorough review by PhD professionals" is basically the approach that the best pre-Wikipedia encyclopedias took. It certainly lead to more consistency, but the breadth and depth was *pathetic* compared to Wikipedia. Choosing a random example, look at our proton-proton chain article and then look at Brittanica's attempt. Theirs is only 310 words long, which is about the same as the *lede* for our article. There's just no competition, and the way Wikipedia got that awesome is because 1) it's not locked down waiting for a thorough review by PhD professionals, and 2) some small percentage of people who see a problem hit the "Edit" button at the top right and fix it. --Sean 15:37, 10 February 2011 (UTC)

Wikipedia is great, but there is still an underlying tension about the role of expertise. I can see whether a physics article is readable or unreadable, but I usually don't touch the article for fear of messing it up. Actually, what I really need to see is whether it is a topic that I could, as a non-scientist, access, or whether it is so involved that there is no point in even trying to present it to non-specialists. Itsmejudith (talk) 16:58, 10 February 2011 (UTC)

I agree Wikipedia is painfully uneven. But the alternative model where only experts edit things simply doesn't work at Wikipedia scale. Citizendium follows some variant of that model; here's their version of the proton-proton chain topic I mentioned. --Sean 17:44, 10 February 2011 (UTC)

@Itsmejudith: There is no tension about the role of expertise. Wikipedia embraces experts and unambiguously benefits more greatly when experts contribute in their fields of expertise compared to amateurs. What Wikipedia has no tolerance for is either a) using unconfirmed claims of expertise as a means to win arguements (as in "I'm an expert so I win") or b) blunt arrogance and rudeness based on those same unconfirmed claims of expertise. Insofar as true experts in their fields have access to better sources than the average Joe, and insofar as they can write well, and insofar as they are willing to write in Wikipedia's house style, then I can't see where Wikipedia is intolerant to experts, as it is often claimed. Wikipedia is intolerant to arrogant people who assume that if they have (or claim to have) expertise in an area that the goals and aims and community norms of Wikipedia don't apply to them... --Jayron32 18:00, 10 February 2011 (UTC)

On a systemic level, the difficulty with experts is in part because there are a small number of experts and a large number of non-experts. On Wikipedia, numbers matter — for establishing consensus, for maintaining articles, for watching things over. If we highly value expertise, a Wiki is a bad model for that. I think Wikipedia is a very frustrating place to be an expert. That's inherent to the system. There are advantages to not worrying about expertise — mainly, you can draw from a much wider editor pool, and raw numbers of editors do produce certainly more volumes of material. But there are also obvious disadvantages as well; there are plenty of things on here that an expert would notice as wrong in a moment. --Mr.98 (talk) 19:01, 10 February 2011 (UTC)

And for which they are allowed to provide sources and make a logical arguement from them, just like anyone else. The problem you note has nothing to do with experts vs. nonexperts. Any group of editors with an agenda to push can easily coordinate their efforts to bring "numbers" to their side in an arguement. Which is why, for article content, we demand sources. Which is what experts have access to. --Jayron32 23:08, 10 February 2011 (UTC)

IP's statement "Wikipedia is ONLY for the casual whatever-ist" is completely untrue in practice, and really should not be true. I use the more specialized articles all the time in research, granted usually with supplements, but you should not try to resist the fact that this is an extremely convenient, well-indexed source. Textbooks are no better or worse for learning a subject independently, and far far worse for reference. That said, the lede does need to be visual/conceptual and not algebraic or definitive, even when I know the subject.

In the case of Conservation of mass, there is a conflict in the lede between expressing "how do I use it and when is it useful in practice" (for science folk) versus "what is the concept, its background, and its historical/scientific context" (for humanities or lay folk). Energy is a complete mess of a concept itself (being used in so many ways with so many definitions, and that's just for scientists), so one should give the article lede a bit of leeway for trying to make sense of it. Of course, all of this should be overcome by talented science pedagogy, a very difficult thing to get. SamuelRiv (talk) 18:10, 10 February 2011 (UTC)

True regarding the need for technical detail in Wikipedia articles. They should have writing which is accessible to BOTH experts and casual readers. Too often it is one or the other.... --Jayron32 18:23, 10 February 2011 (UTC)

You might want to try WikiBooks as well. ~AH1^(TCU) 22:27, 11 February 2011 (UTC)