Wikipedia:Reference desk/Archives/Science/2008 April 16

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April 16

What cant I split an atom with a pair of scissors?

I'm basically asking -why does it take special equipment (or does it?) to split an atom? Is it nature's way of keeping us from blowing ourselves up? There isnt always a bad reaction. Fermilab has been annihilating atoms for years with no ill affects.--Sunburned Baby (talk) 01:37, 16 April 2008 (UTC)

To say it really briefly, it's because the electromagnetic force is much weaker than the nuclear force. Wrad (talk) 01:46, 16 April 2008 (UTC)

[edit conflict]Blades are made of atoms themselves. Try to imagine one spherical atom splitting another and you might get a sense of why it doesn't work. It's actually a lot more complicated than this, because atom-splitting is not a mechanical process... see nuclear fission for details. --Allen (talk) 01:51, 16 April 2008 (UTC)

I think the answer is because you (a mere human being I am assuming) are unable to input enough energy into the scissors to achieve atomic splitting. Fermilab has lots more energy available. On the other hand, if you were to somehow arrange to drive the handles of the scissors together with the energy of, say, a hydrogen bomb then you would end up splitting quite a lot of atoms. SpinningSpark 07:45, 16 April 2008 (UTC)

Also keep in mind that your scissors is also made of atoms. Even if you have the finest edge possible on your scissors, it will still be at least one atom wide. Due to the difficulty in honing the edge to even that degree, most razor sharp edges are hundreds if not thousands of atoms wide. It's like trying to cut a loaf of bread with another loaf of bread - even if the bread is soft, you're not going to make much headway. -- 128.104.112.85 (talk) 21:45, 16 April 2008 (UTC)

Also, splitting an atom isn't like cutting a piece of clay. Even if there was a blade that would remain sharp on the atomic scale (which is impossible) it would not be able to 'cut' an atom. Splitting an atom requires a lot of energy to be concentrated on the atom. Ilikefood (talk) 22:36, 16 April 2008 (UTC)

Actually, splitting a single atom would require very little energy, just concentrated into a small space, which is the hard part. I would also release very little energy. The only reason an atom bomb works is because many atoms are split in a chain reaction. Also, an H-bomb doesn't split atoms, it fuses them (see nuclear binding energy). —Preceding unsigned comment added by *Max* (talk • contribs) 01:22, 17 April 2008 (UTC)

True, an H-bomb is a fusion device, but the energy released is so large that fission occurs as a secondary effect. Items exposed to the e-m and neutrino radiation can become hot with fission product radiation even when not exposed to fallout. SpinningSpark 00:31, 19 April 2008 (UTC)

I would guess that you could split many atoms with a pair of scissors. You'd just need to ensure that the speed at which the scissors and target strike each other is around the speed of light. StuRat (talk) 16:53, 17 April 2008 (UTC)

Also, an atom is a tiny nucleus surrounded by a large cloud of electrons. To split an atom, you need to get at the nucleus. Imagine the previous poster's comment about loaves of bread, but imagine that there is a frozen pea in the middle of each loaf. Splitting the atom is more like splitting that pea. --Slashme (talk) 09:08, 22 April 2008 (UTC)

The forces holding atoms together are far stronger than the forces holding atoms to each other in a molecule, which are far stronger than the forces holding molecules together in a cellular structure in a wood fiber, and so on. Ziggy Sawdust 23:40, 22 April 2008 (UTC)

Gravity and M-Theory

Since gravity is defined as known to be a bending of space-time, why should it be mediated by bosons? Bosons mediate forces, and it doesn't seem that a bending or curvature of something is an actual force.

Defined? I'm not sure defined is the right word. It certainly seems to work to model gravity as a deformation of spacetime, but I'm not sure physics is so brazen as to claim to define a fundamental force. But then, there are those who figure things like wormholes must exist because of the model, so maybe I'm wrong. Theories and thought experiments are wonderful things, but I personally find it most constructive to keep my mind open either way, especially given the situation where two (or more) theories seem to work for some things but conflict with each other intuitively. --Prestidigitator (talk) 04:10, 16 April 2008 (UTC)

Actually the forces of the standard model are not-forces in pretty much the same way that gravitation is not a force. All of the standard model bosons (except the Higgs) are gauge bosons, meaning that they all arise from principles of gauge invariance that are very similar to general covariance. In the case of electromagnetism the gauge group is U(1), which is the group of continuous symmetries of a circle. You can think of this as saying that every point of spacetime is really a little circle (that is, spacetime is really $\mathbb {R} ^{4}\times S^{1}$ rather than $\mathbb {R} ^{4}$), and the so-called "force" of electromagnetism is the result of moving geodesically through a spacetime where the circles at different points are rotated relative to each other. This idea was worked out in detail long ago and is called Kaluza-Klein theory. In Kaluza-Klein theory you have a five-dimensional metric tensor which looks something like $\left({\begin{smallmatrix}g&A\\A&\phi \end{smallmatrix}}\right)$, where g is the 4×4 metric tensor from general relativity, A is the electromagnetic four-potential (written once horizontally and once vertically—the matrix is symmetric), and φ is a scalar (spin 0) field which has never been observed, called the dilaton (or radion or graviscalar). The source of the five-dimensional curvature is a five-dimensional stress-energy tensor which contains the 4×4 stress-energy tensor, the four-current, and the scalar charge packed together in a similar way. Unfortunately, quantizing this theory and extending it to the other forces has turned out to be amazingly difficult, but everyone expects that when/if we finally manage to do it, all of the forces will look like different aspects of the same thing, because they already look like different aspects of the same thing. -- BenRG (talk) 12:19, 16 April 2008 (UTC)

In M-Theory and string theory, are the strings described composed only of energy? If not, what else are they composed of? Zrs 12 (talk) 01:57, 16 April 2008 (UTC)

They aren't really composed of anything, otherwise the theory wouldn't be about strings but about whatever the strings were made of. They have energy and charge, in the sense that they behave (interact) how you'd expect things with that energy and charge to interact. Energy is nothing more or less than gravitational charge; it's not a substance you can make things out of any more than electric charge is. -- BenRG (talk) 12:19, 16 April 2008 (UTC)

Rube Goldberg question

How can one domino initiate a 'process' on a single, compact Rube Goldberg machine that is on a flat surface? --hello, i'm a member | talk to me! 05:06, 16 April 2008 (UTC)

Any machine is all about transferring energy. A falling domino releases potential energy, converting it to kinetic energy that then triggers some other release of potential energy (knocking over another domino, for example) or transfers the kinetic energy to another object (starting a ball rolling), etc. Standing up all those dominoes creates a whole bunch of potential energy, but it needs some input (a finger, a feather, a bowling ball) to make the first one fall. That probably doesn't answer the question, but I don't entirely understand the question... DMacks (talk) 05:49, 16 April 2008 (UTC)

Real time kinematic GPS positioning

Your article on Real time kinematic GPS positioning contains the statement "This integer ambiguity problem can be addressed to some degree with sophisticated statistical methods that compare the measurements from the C/A signals and by comparing the resulting ranges between multiple satellites."(integer ambiguity) in red.

I would like a more comprehensive (but readable) account of this subject. From other research, I have found that explaination of this topic are illusive, but perhaps Wiki has the resources to find what I (and others) need.

Thankyou if you can help.

RH.Astrogoose (talk) 05:43, 16 April 2008 (UTC) Retitled for clarity AlmostReadytoFly (talk) 09:29, 16 April 2008 (UTC)

global warming question solved?

How far is the earth from the sun? How has this distance changed in last 10 /100 years? Should we fire retro rockets to alter this distance? —Preceding unsigned comment added by 82.68.203.150 (talk) 09:28, 16 April 2008 (UTC)

It's roughly 150 million kilometres or 93 million miles to the Sun. There's no way we could fire enough rockets to move the Earth a significant amount (the Earth weighs 5.9742 × 10^24 kg), and no sensible way to attach retro rockets to a planet, even if it was considered a good idea. AlmostReadytoFly (talk) 09:34, 16 April 2008 (UTC)

Crimes_of_the_Hot. Not really a solution though... 130.88.140.121 (talk) 11:50, 16 April 2008 (UTC)

Actually it's fairly easy to attach rockets to the earth. Ground tests of rocket engines are designed to be stationary with respect to the earth. The hard part is really conveying the momentum to the entire planet, rather than to miniscule local deformations of the terrain. Nimur (talk) 16:02, 16 April 2008 (UTC)

The hard problem is to prevent the exhaust being stopped by the atmosphere. Else it will only move a bit of exhaust and air up and ground down, and this change will be reversed by Earth's own gravity. Even if there were no atmosphere, chemical rockets wouldn't do it because the best ones currently only achieve about 4.5 km/s exhaust velocity, lower than the 11.2 km/s escape velocity. So the exhaust would move up, Earth would move "down", and gravity would revert that change again. Icek (talk) 19:36, 16 April 2008 (UTC)

Also anything we build on earth is travelling the same speed as the earth (law of inertia). the rockets will need to create momentum greater than the orbiting earth to knock it to a larger orbit. The exhaust, disruption will be far greater than this global warming problem you try to solve. Besides, the earth's orbit has been stabilised for millenia to millions of years, whichever your point of view is. Any attempt to change it will end up being stabilised back to its current state again. --Kvasir (talk) 20:45, 16 April 2008 (UTC)

Please try not to post answers when you don't know what you're talking about. It is true that changing the Earth's orbit using rockets is not feasible for many reasons, but a "need to create momentum greater than the orbiting earth" is not one of them; the rocket would only have to alter the momentum by a small fraction relative to the whole amount. And the orbit is not "being stabilized"; it doesn't change much because there isn't anything acting to change it much, that's all. --Anonymous, 22:45 UTC, April 16, 2008.

Like I say, no sensible way to attach functioning "retro-rockets" to the earth. Of course it's possible to ground test rocket engines and not push the planet anywhere. AlmostReadytoFly (talk) 22:41, 16 April 2008 (UTC)

Global warming has little to do with the Earth-Sun distance. For example, see Ice age. For more details about variations in the Earth-Sun distance see Earth#Orbit and rotation.--Shantavira|^{feed me} 12:41, 16 April 2008 (UTC)

Over the very long term (too long, in fact, to be of any relevance to the solar system), the Earth is receding from the Sun for the same reason the Moon is receding from the Earth -- tidal forces. However, the Earth-Sun recession is on the order of one micrometer per year, or about 5 km (out of 150 million km) since the solar system formed. Additionally, the conversion of (a small part of) the Sun's mass to energy causes Earth's orbit to widen, though again, this effect is insignificant next to other orbital characteristics. — Lomn 13:07, 16 April 2008 (UTC)

It's probably a bit more than that, since the Sun is shrinking by a fair bit every year as it burns up. I can't remember how much, but it is certainly measurable - if you could get near it with a tape measure. 195.60.20.81 (talk) 14:30, 16 April 2008 (UTC)

It should be about 2 cm per year, from an estimate based on orbital energy change. Icek (talk) 19:30, 16 April 2008 (UTC)

Environmental Impact statement writer

I'm learning about Environmental Impact Statements in class, and I was wondering, (because I find biology to be fun and fascinating) who writes these exactly? What would be the title of that profession? 69.16.91.28 (talk) —Preceding comment was added at 09:56, 16 April 2008 (UTC)

Depending on what impacts they are looking at they could be quite varied. Ecologist, Toxicologist, Environmental Engineer, Environmental Biologist, Environmental Chemist, to name a few...--Shniken1 (talk) 11:30, 16 April 2008 (UTC)

How to save worlds power crisis

Take an Extension cord and plug it into itself. The powr shud then go round and round and come ot of the other sockets. —Preceding unsigned comment added by 213.38.213.226 (talk) 10:24, 16 April 2008 (UTC)

Haha. Why don't you try it and tell us if it works? AlmostReadytoFly (talk) 10:28, 16 April 2008 (UTC)

Brilliant. It will make my cold-fusion device and perpetual motion machine obsolete. -- Q Chris (talk) 10:36, 16 April 2008 (UTC)

It doesn't seem to work. I will check fuses and plugs and ley you know. -- 213.38.213.226 (talk) 10:45, 16 April 2008 (UTC)

Maybe you should try reversing the polarity of the neutron flow, or even try attatching it to a Flux capacitor. Ilikefood (talk) 22:38, 16 April 2008 (UTC)

Just don't cross the beams. --Prestidigitator (talk) 04:11, 17 April 2008 (UTC)

You don't need fuses and plugs and wires. You just need a waterwheel - like this one. Gandalf61 (talk) 11:31, 16 April 2008 (UTC)

Just in case this is a serious question (I'm never sure), unfortunately your solution won't work, as it violates the Law of Conservation of Energy - you can't get energy out of nothing. Sorry! — QuantumEleven 12:04, 16 April 2008 (UTC)

Thanks, sorry for the silly question. —Preceding unsigned comment added by 213.38.213.226 (talk) 10:05, 17 April 2008 (UTC)

What's the 'law' by which you can never be sure whether someone on the internet is being serious in this sort of situation? 130.88.140.121 (talk) 12:23, 16 April 2008 (UTC)

Because there is no way to determine the age, IQ, motive or demeanour of the writer.--Shantavira|^{feed me} 12:44, 16 April 2008 (UTC)

I believe there is an actual 'law' in the spirit of Godwin's law and rule 34, but I can't remember which it is myself. Perhaps it is in List of eponymous laws? Skittle (talk) 15:20, 16 April 2008 (UTC) Possibly Poe's Law? Skittle (talk) 15:24, 16 April 2008 (UTC)

You can't just plug an extension cord into itself. You have to plug it into the mains until it fills up with magic smoke, then plug it into itself before any of it leaks out. 206.252.74.48 (talk) 13:11, 16 April 2008 (UTC)

This only works if you have one end plugged in to a socket in your house and the other end plugged in to a neighbours house on a different phase. Like magic, you will get lots of smoke (don't try this at home) SpinningSpark 14:39, 16 April 2008 (UTC)

Now assume the extension cord is superconductive. Does that change the answer? Edison (talk) 02:45, 17 April 2008 (UTC)

(Sigh). Assume good faith. In general, the consumers ( plugged into the cord) expect a continuing source of power. When you remove the original power source by unplugging the extension cord, you remove that power source. Even if you assume a theoretical switching time of zero, the amount of energy in the closed system is constant, so the energy will fall over time. For practical circuits, the voltage will fall to zero in less than one second._Arch dude (talk) 03:30, 17 April 2008 (UTC)

But what if the extension cord were made of superconductors and several light-years long and the Alpha Centaurians had conveniently left it plugged-in to their mains for several years? (And let's ignore the need for voltage converters.) (Extra credit: And what if they then "tugged" on the cord?)

Atlant (talk) 13:58, 17 April 2008 (UTC)

The article Superconductivity says "An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source." "Indefinitely" really means no drop expected in hundreds of thousands of years. This is not in accord with your statement that the voltage would drop to zero in less than one second (for a normal extension cord of even hundreds of feet current would disappear orders of magnitude faster than one second). (And please avoid starting answers with "(Sigh). Assume good faith." Edison (talk) 00:16, 19 April 2008 (UTC)

• If you actually plugged anything into the loop, the current would drop off immediately, because the amount of energy stored in the loop would not be very large.
• "Indefinitely" doesn't necessarily refer to thousands of years. If I say that a teenager will stare at MTV indefinitely, I'm talking hours. If I say that the traffic problems we are experiencing in our cities will continue indefinitely, I'm probably talking decades to centuries. --Slashme (talk) 09:25, 22 April 2008 (UTC)

Try putting a fan in a rowboat, and attaching a sail in front of it. NOTE: It took me upwards of 2 years to figure out why that wouldn't work. Ziggy Sawdust 23:40, 22 April 2008 (UTC)

masturbation as exercise

A couple of years ago, I heard masturbation burned an inordinate amount of calories and/or fat. Is this true, or did I step in hip-deep bullshit? This IS a serious question. --AtTheAbyss (talk) 12:48, 16 April 2008 (UTC)

Hip-deep. Sex is reasonably good exercise, but that's more a full-body thing. — Lomn 12:57, 16 April 2008 (UTC)

It must burn a few calories. In fact, I would go so far as to say that most men must burn thousands of calories choking the chicken every year. But only through diligence and application, not because it burns more calories than it should. 195.60.20.81 (talk) 14:03, 16 April 2008 (UTC)

Obviously it will depend on many factors, but vigorous sex itself only burns about a calorie and a half a minute. Masturbation is certainly a lot less than that. It's not very much exercise. --Captain Ref Desk (talk) 16:26, 16 April 2008 (UTC)

So why do I feel more knackered after bashing the bishop than after a run round the block?--Shantavira|^{feed me} 07:38, 17 April 2008 (UTC)

I do not know if it is a good exercise but the sperm in the semen requires fructose and galactose (sugars) to survive so technically it removes sugar, which is energy, from the body.--Lenticel ^(talk) 21:51, 16 April 2008 (UTC)

To burn calories from fat, you must burn the readily available energy in the blood. That takes time. Masturbation rarely lasts that long. To get any cardiovascular benefit, the heard rate must be increased. I don't know of anyone breaking a major sweat with a racing heartbeat after masturbation (unless they are very VERY out of shape). The removal of sperm isn't a substantial removal of energy. They were going to die soon anyway and need to be replaced. So, all in all, masturbation is not a good replacement for real exercise. As for that "worn out" feeling, it is commonly called "euphoria" and is a normal reaction to orgasm. -- kainaw™ 18:42, 17 April 2008 (UTC)

Maybe it can be used as a "warm-up" for real exercises.:) --Lenticel ^(talk) 21:52, 17 April 2008 (UTC)

Because if you're moving your legs to go around the block, the total movement is larger, but it's spread among the different parts of the legs. Your hands aren't designed to move in a repetitive motion like that with (some) force for as long as it takes to get it over with. Of course that depends on how long it takes you individually. Ziggy Sawdust 23:38, 22 April 2008 (UTC)

japanese maple grafted

My japanese maple tree (red w/8 - 9 points on the leaves) apprears to have been grafted with a root of a weed. The tree has taken on characteristics of the weed and the maple. The top half of the tree is green like the weed, the leaves of the new growth now have 4 points. I can see there the green from the weed has grown inside the trunk of the maple. Probably a time where the viny weed attached itself to the trunk of the maple. My question is, can I cut the top half of the tree down so I only have the maple left. Will this give me a permanent fix or should I just cut the tree down? Enduranceprincess (talk) 13:19, 16 April 2008 (UTC)

What kind of weed? A weedy maple? I don't think it would be possible to graft a maple with anything but another maple. And four points on a maple leaf is unusual; all maples I've seen have odd numbers of points, not counting a few individual leaves here and there. Could you upload a photo? --Allen (talk) 06:37, 17 April 2008 (UTC)

A little patient tree surgery is likely better than just chopping a tree down (unless you're looking for a reason to clear it). It appears maybe even a weed seed got locked in there somewhere, early on. Luckily the two plants are very different which would make it easier. I would go to the lowest point of the weed that you can find and cut through or ringbark it there. The rest should die off and could then be cut away. Julia Rossi (talk) 00:32, 18 April 2008 (UTC)

Price of oil and other products

I was reading about the current oil crisis and was wondering about the effects that the rising cost of petroleum will have on industrial and consumer goods. We're talking about a 300 $/gallon barrel in a few years from now. ADM (talk) 13:31, 16 April 2008 (UTC)

• Will people drive less cars and use more bicyles ?
• Will plastic bags become eco-friendly ?
• Will airplane tickets be more expensive ?
• Will ethanol be produced in a safer way, as to not impact on food markets ?
• Will refineries switch to coal production ?
• Will investors begin to speculate on the price of water, making it much more expensive ?
• Will things like oil-based lubricants used in condoms and on shoe polish become more expensive ?
• Will the environment ultimately benefit from expensive oil ?
• Will societies have to reflect on what modernity means without oil ?

• Will people drive less cars and use more bicyles ?

There has been a boom of bicycle use in Western nations in the last decade, and the trend is likely to continue. However, bicycles are in sharp decline in developing nations, so overall, I doubt it.

• Will plastic bags become eco-friendly ?

Plastic bags cost next to nothing to produce, and even if their production price goes up by a factor of 10, they will still be very cheap. But hopefully, people will become more sensible and use backpacks for shopping instead of plastic bags.

• Will airplane tickets be more expensive ?

Probably, unless revolutionary progress in fuel-efficiency is made.

• Will ethanol be produced in a safer way, as to not impact on food markets ?

Ethanol production will always impact on food markets because ethanol crops compete for land with food crops. It doesn't make a difference how you produce it. You still need the land.

I disagree. Ethanol could be produced from waste products of food production, like corn husks. This would actually decrease the cost of the corn. It can also be produced by waste products from other sources, like underbrush removed from national parks to prevent fires. It could also be potentially produced from aquatic or marine organisms, either in lakes or oceans, or relocated to roofs of existing buildings. StuRat (talk) 16:24, 17 April 2008 (UTC)

• Will refineries switch to coal production ?

Probably not. Refineries are not equipped to process coal. New coal gasification plants might be built.

• Will investors begin to speculate on the price of water, making it much more expensive ?

No, because water is not a commodity, since it can't be shipped around the world at a competitive price. However, investors will speculate on water companies (and are indeed doing so already - water-based investment funds are available as a consumer product)

• Will things like oil-based lubricants used in condoms and on shoe polish become more expensive ?

A little, but not significantly. The commodity price is only a small fraction of the manufacturing cost of those products. Cambrasa 13:56, 16 April 2008 (UTC)

A slightly different take...

• Will people drive less cars and use more bicyles ?

- There may be a dip but it is hard to say - the difficulty with the prediction is that any decline in developed nations might be surpassed by increase in developing nations

• Will plastic bags become eco-friendly ?

- They already are. The problem is their recycle rate. You have to look at the full life-cycle of a product. The site i was going to link to (http://www.ilea.org/) seems to have been replaced which is odd - but the research suggest that it depends on what % are recycled as to whether it is better or worse than paper/canvas bags for the environment (and again their respective recycling affects it too)

• Will airplane tickets be more expensive ?

- I suspect this will very much depends on tax policy country-by-country. Whether they rise faster than the increasing wealth of people in each nation is perhaps a more difficult question to answer.

• Will ethanol be produced in a safer way, as to not impact on food markets ?

–

• Will refineries switch to coal production ?

- Well coal production already exists on a massive scale, i'm sure some movement to coal will happen where economically viable

• Will investors begin to speculate on the price of water, making it much more expensive ?

- Water prices already rise and fall according to market expectations of utility-companies/real-costs of their business, it's unlikely this will change in the future

• Will things like oil-based lubricants used in condoms and on shoe polish become more expensive ?

- It depends on what oil is used, I doubt demand will outstrip supply enough to make these things vastly more expensive

• Will the environment ultimately benefit from expensive oil ?

- The optimist's theory is - yes. As oil becomes expensive the viability of alternative increases. That new fuel that is too expensive to compete might suddenly become more attractive, it might attract more attention of investors/scientists/inventors etc. The governments of the world can help by giving incentives to invest in sustainable fuels and by giving short-term tax-breaks until new technologies replace old at which point the tax can increase (this is why so many people moan about "you got us hooked then increased the tax" - yes they did because it was a policy designed to move you from X to Y and once that was achieved the established technology could pull in valuable tax)

• Will societies have to reflect on what modernity means without oil ?

- Of course, though 'without oil' is not what is likely to happen. Likely the last barrels of oil will never be taken, but the world will adapt to the replacement that comes our way - that much is pretty certain. The doomsayers over-estimate the flexibility of mankind. It'll be tough, and I agree it is likely to lead to more international instability, perhaps even wars over energy/food/water as we adapt, but in the long-term things will progress. ny156uk (talk) 21:25, 16 April 2008 (UTC)

Surely the doomsayers underestimate the flexibility of mankind. Or perhaps you meant they think mankind will be so flexible it will tie itself into pretzel-shaped knots. :-) StuRat (talk) 16:29, 17 April 2008 (UTC)

RNA

What kind of molecules catalyze RNA splicing? I can't find an answer that I understand. Thank you. --Freiberg, Let's talk!, contribs 16:29, 16 April 2008 (UTC)

See Splicing (genetics). Interestingly, the splicing machinery consists of RNA molecules. —Preceding unsigned comment added by 128.163.194.164 (talk) 17:12, 16 April 2008 (UTC)

snRNPs, mRNA and non-snRNPs are all involved, and make up the splicesome. Wisdom89 _{(T / ^C)} 21:28, 16 April 2008 (UTC)

Precipitation (in a chemistry context)

Let's say you've got a chemical solution; some reaction takes place and small bits of a solid form in the solution. If the solid bits float to the top of the liquid instead of sinking to the bottom, is it correct to call this precipitation? I usually think of precipitation meaning falling. Is there a better word for the situation I've described? ike9898 (talk) 17:17, 16 April 2008 (UTC)

Precipitation is the general formation of an insoluble solid from a solution, so float or sink, it's precipitation. Someguy1221 (talk) 17:35, 16 April 2008 (UTC)

• " If you are not part of the solution, you are part of the problem." Ghandi.
• "If you are not part of the solution, you are part of the precipitate." (anonymous chemistry student.)

by this definition, it does not matter whether the result's density is greater or lesser than the density of the remaining solution. The result is still precipitate. -Arch dude (talk) 03:16, 17 April 2008 (UTC)

Yes, the raining scientists seem to have decided that it snow difference if it sinks or swims, it's still a precipitate. All hail the scientists for this precipitous decision that has removed the fog from our eyes. StuRat (talk) 16:11, 17 April 2008 (UTC)

Family Guy Science

There is a clip from family guy in which Brian demonstrates to Peter that Peter has gravitational pull. Before long, an apple, a picture frame, a glass of ice water, and a tv set are all in orbit around Peter. Just how fat would Peter have to be for this to actually happen? --Omnipotence407 (talk) 21:36, 16 April 2008 (UTC)

On earth, he's have to be more massive than the earth, which would cause its own problems. In space, outside of the influence of other bodies, he's probably already fat enough. Gravity only depends on mass and distance. Since Peter isn't a spherical object, though, it would be difficult to actually get an orbit working. It is more likely that all the objects would orbit a common lagrange point. --Mdwyer (talk) 22:18, 16 April 2008 (UTC)

Actually, this isn't quite true. He could be a lot less massive than Earth if he was a lot denser than Earth - but this would require him to be made out of some exotic matter like neutronium. Cambrasa 23:30, 16 April 2008 (UTC)

Watch the show sometime and then let us know if you still think Peter isn't incredibly dense. DMacks (talk) 23:36, 16 April 2008 (UTC)

Take a look at Hill sphere for the math behind this. — Kieff | Talk 07:51, 17 April 2008 (UTC)

What, no King of the Hill sphere ? StuRat (talk) 16:05, 17 April 2008 (UTC)

Also note that if something was to orbit Peter in space, at his current mass and volume, it would orbit extremely slowly, perhaps taking many years to complete one orbit. StuRat (talk) 16:03, 17 April 2008 (UTC)

The presence of atmosphere also makes the events of this video clip highly unlikely. Thermal collisions and convective air motion would interfere so greatly with the orbiting objects that they would promptly decay. Nimur (talk) 17:21, 17 April 2008 (UTC)

If we ignore atmospheric effects and the confounding effects of earth's gravity (say we put Peter into deep space), you can calculate the needed mass with the formula given at Orbital mechanics#Circular orbits. v = sqrt(GM/r) or M = r*v²/G If I remember the clip correctly, the objects orbited at arms length or so (say 1 m), with a period of 5 seconds or so. The velocity of the orbiting objects was thus 2*π*r/t (one circumference per orbit) or v ~= 1.26 m/s. Plugging into the above equation, we get M ~= 2.4 × 10¹⁰ kg, a little less than one tenth the mass of all people on earth, or about 4 Great Pyramids of Giza (according to Orders of magnitude (mass)). -- 128.104.112.85 (talk) 18:26, 17 April 2008 (UTC)

Mass spectrometry

Hello. I am in grade 12 high school (last year before university). Our chemistry teacher told us that a mass spectrometer is used to determine the relative mass between isotopes of the same element. However, our article indicates that the exact atomic mass of an element can also be determined by a mass spectrometer. How does the two techniques differ? To find the exact atomic mass, does the spectrometer have to find the volume and density, and therefore mass, of the particles or something? Peace. Applefungus (talk) 21:30, 16 April 2008 (UTC) (moved by BrainyBabe (talk) 22:33, 16 April 2008 (UTC))

A mass spectrometer measures the mass(es) of the molecules (and ionic fragments) in a sample, each one on its own (not in a macroscopic lump of sample). It reports how much of each mass was present. I'm not sure how "determining the relative mass between isotopes of the same element" differs from just measuring the mass of each? If I measure a sample of C-12, I get a signal indicating the presence of particles having a mass of 12; if I measure a sample of C-13, I get a signal indicating the presence of particles having a mass of 13. Perhaps you're thinking of the relative amounts of isotopes in a sample of a certain element? If I measure a sample of "carbon", I would expect to get a signal for 12 mass units that is 99 times as strong as the signal for 13 mass units, which corresponds to the natural-abundance isotopic mixture of 99:1 C-12:C-13. DMacks (talk) 22:45, 16 April 2008 (UTC)

Mass spectrometers can only measure mass/ion ratios. That is a singly charged ion of carbon-12 will M/Z ratio of 12, a doubly charged will have a ratio of 6, ect. Carbon-13 will have ratio 13, and 7.5 respectively. As DMacks said the C-12 signal will be 99 times stronger than C-13. The exact ratio you get for a singly charged species is the exact atomic mass for that atom. The numbers you see on a periodic table for the "atomic mass" are relative atomic masses, these include all naturally occuring isotopes and thier relative abundances to give an average mass per atom of a natural sample of that element.--Shniken1 (talk) 23:28, 16 April 2008 (UTC)

An "element" does not have an exact atomic mass. A particular isotope of an element does have a precise atomic mass. The "atomic mass of an element" is actually the weighted average of the atomic mass of its isotopes, weighted by the relative prevalence of the element's isotopes as found in nature. This definition of atomic mass is used because chemists were measuring atomic mass before there was any way to separate the isotopes. A mass spectrometer is the ideal instrument to separate the isotopes of an element. It can determine with absolute accuracy the ratios of the isotopes of an element in a particular sample, for example the ratio of carbon 12 to carbon 14 in a particular ancient tree ring. The atomic mass of pure carbon 12 is fixed by the laws of physics. The same is true of the atomic mass of carbon 14. The atomic mass of "carbon" is a number negotiated by humans, based on a consensus as to the ratio of carbon 12 and carbon 14 in a "natural" sample of carbon. -Arch dude (talk) 01:45, 18 April 2008 (UTC)

Incidentally, this is an extremely high-quality question from a grade-12 student. -Arch dude (talk) 01:48, 18 April 2008 (UTC)

The way mass specs measure mass is by using a magnet to bend the trajectory of the ionized (charged) compound. The compound is shot through something, becomes ionized, and as you may know things that have charge can be affected by magnetic field. The machine measures how much the trajectory was affected by magnetic field. The more mass something has, the harder it is to bend its trajectory.

Variation of Young's Modulus with purity of a metal

Hello, this is a bit dry, and maybe a long shot. But I'm looking for information (preferably a study) on the variation of Young's (i.e. elastic tensile) modulus with degree of purity for a metal (preferably copper). Any ideas?

Eth (talk) 23:30, 16 April 2008 (UTC)Eth

I'd expect you to find the best results for steel, probably for different alloys with different amounts of carbon, etc. (I suppose those aren't technically "impurities", as they have been intentionally added in many cases.) Carbon in steel, for example, makes the steel harder/more brittle. StuRat (talk) 15:55, 17 April 2008 (UTC)

Weird lead things

My father ordered me some very strange things on eBay and seems to have forgotten what they were actually used for. They are two lead cylinders with bottoms and removable tops. They each weigh around 10lbs apiece, I estimate. He claims they have something to do with atomic research. Any guess as to what they are? They look like they could hold radioactive sources in them or something like that. Should I be concerned about keeping things inside them now? I guess I could take it in and see if someone could run a Geiger counter on one of them... sigh. Any thoughts? --Captain Ref Desk (talk) 23:55, 16 April 2008 (UTC)

I'm having visions of a certain episode of House MD right about now. Get them checked out before you mess around with, or even go near them. --Kurt Shaped Box (talk) 23:58, 16 April 2008 (UTC)

OK, I figured it out. They are lead pigs. Very odd. I imagine I should not store things in them but otherwise they are probably as safe as any other 10lb chunks of lead? --Captain Ref Desk (talk) 23:59, 16 April 2008 (UTC)

If they've been used for atomic research, there is a chance that whatever they once held has left a residue inside - poss. radioactive. You want to take a chance with radiation? --Kurt Shaped Box (talk) 00:26, 17 April 2008 (UTC)

Sure. It's a lot of lead. Whatever was once inside is not getting out, even if there is some residue. It's just a question of not putting things inside it. Anyway, I'm not suffering from radiation sickness having taken a look inside, so from that point of view it's not something immediately fatal. ;-) --Captain Ref Desk (talk) 16:45, 17 April 2008 (UTC)

If there ia any contamination, then somebody broke the law before they showed up on eBay. Depending on where you live you can probaly find a local university lab that will asses these for you at no cost. If not, and if you are paranoid, then simply bury them and go to the local HomeDepot, buy sheet lead, and roll it into cylinders. -Arch dude (talk) 03:06, 17 April 2008 (UTC)

But then I'd still have totally useless lead cylinders. ;-) --Captain Ref Desk (talk) 16:45, 17 April 2008 (UTC)

No costs "asses" ? Cool. No more need to covet your neighbor's... :-) StuRat (talk) 15:50, 17 April 2008 (UTC)

I believe that eBay does sell radioactive materials, so long as the level of radioactivity is below what would be considered dangerous. Many watch faces, for example, are slightly radioactive. StuRat (talk) 15:57, 17 April 2008 (UTC)

eBay does definitely sell radioactive materials of low grades. Do a search for "uranium ore" and you'll find all sorts of pretty alpha sources. --Captain Ref Desk (talk) 20:38, 17 April 2008 (UTC)

Smack them together and if you find yourself instantly transformed into a cloud of plasma, they might be a bit radioactive... :-) Ilikefood (talk) 22:21, 17 April 2008 (UTC)

I somehow doubt that the poster's dad successfully bought munitions-grade uranium or plutonium over e-bay. --Slashme (talk) 09:49, 22 April 2008 (UTC)

Must differentiate between radioactive contamination and radioactivity. Pigs may be contaminated or radioactive (I think) or both! Not sure if lead can be made radioactive by exposure to nuclear radiation. Anyone know?

A non-radioactive substance cannot, usually, become radioactive itself. Otherwise all our smoke alarms would be deadly. It can become contaminated just by having trace amounts of a radioactive material on it. I'm pretty sure that with lots and lots of energy, lead could become radioactive?

Luxosus (talk) 14:36, 19 April 2008 (UTC)

Actually, this is not really true. If an object of almost any kind is irradiated with sufficiently hard radiation, nuclear reactions will take place in the matrix of the material; some of the products of these reactions may well be radioactive. High-energy neutrons, for example, could render almost anything radioactive. --Slashme (talk) 09:49, 22 April 2008 (UTC)