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September 29

A system of two electrons

They are initially released at infinity (zero potential energy). One has a velocity of +v, and one has a velocity at -3v. I'm supposed to find out their minimum separation....

By conservation of momentum, I know that the total momentum of the system is always -2mv and that the overall internal energy of the system has to be 5mv^2 (0.5m(3v)^2 + 0.5mv^2).

At minimum separation, both particles are travelling in the same direction in the negative x-direction, with equal velocities (hence separation is not changing). If their overall momentum is -2mv and their kinetic energies are equal, then their overall kinetic energy must be mv^2, yes?

So this means 4mv^2 must be stored in electric potential. Since potential energy for each charge is kq^2/r, overall potential energy is 2kq^2/r. 4mv^2 = 2kq^2/r, so r = kq^2/2mv^2. However the program says this is the wrong answer. Help? John Riemann Soong (talk) 03:38, 29 September 2010 (UTC)[reply]

If I understand the question: Why would they be traveling in the same direction at minimum? Wouldn't they bounce off of each other? The overall momentum is a red herring - they only thing you care about is the relative velocity (which is 4v), the absolute velocity is meaningless. Ariel. (talk) 04:35, 29 September 2010 (UTC)[reply]

Well one is moving faster than the other initially so one would lose its forward kinetic energy more quickly than the other and starts going in the other direction. Minimum separation is achieved when their velocities are equal. Well, I fixed it anyhow. The key was that potential energy of the charge pair was kq^2/r, not 2kq^2/r. John Riemann Soong (talk) 04:59, 29 September 2010 (UTC)[reply]

I guess I didn't understand the question. Ariel. (talk) 06:53, 29 September 2010 (UTC)[reply]

Polyamidoamine epichlorohydrin

What's polyamidoamine epichlorohydrin? —Preceding unsigned comment added by Kj650 (talk • contribs) 06:11, 29 September 2010 (UTC)[reply]

here is a pdf about it (got it by typing the above into Google. You can do that yourself too!). It appears to be a polymer composed of three monomer units, those being adipic acid, epichlorohydrin, and diethylenetriamine. From the google search I did, it appears to be used a waterproofing additive to paper; to help paper retain its strength when wet. --Jayron32 06:20, 29 September 2010 (UTC)[reply]

how is it made —Preceding unsigned comment added by Kj650 (talk • contribs) 17:04, 29 September 2010 (UTC)[reply]

Two of the first page of google hits clearly identify themselves as articles or patents related to the manufacture of the chemical. DMacks (talk) 17:42, 29 September 2010 (UTC)[reply]

Physics: charges

Imagine that the sun carries a net excess positive charges while the earth carries a net negative charge. If the excess charge is proportional to the mass Q=KM(sun) and Q=-KM(earth), (a) what charges would be needed on the earth and on the sun in order to provide electrostatic attraction equal to the gravitational attraction (b)what is the value of the proportionality constant k(in coulombs/kg)? —Preceding unsigned comment added by 41.204.175.75 (talk) 07:17, 29 September 2010 (UTC)[reply]

This looks like a homework question. The Reference Desks will provide links to useful articles, but there is no benefit to you if we do your homework for you. Dolphin (t) 07:29, 29 September 2010 (UTC)[reply]

I'm not convinced science is Opie's forté. --Sean 16:03, 29 September 2010 (UTC)[reply]

See Coulomb's law. Dolphin (t) 01:45, 30 September 2010 (UTC)[reply]

Question. In such a case -- would the earth suddenly go flying off at a tangent where the new Coulomb force was imposed? Or would it in fact, migrate to a new orbit? John Riemann Soong (talk) 01:51, 30 September 2010 (UTC)[reply]

Ignoring relativistic stuff etc, gravity and electrostatic force behave pretty much the same, so adding these charges would effectively be the same as tinkering with the gravitational constant. The OP's problem is suggesting an attractive force, which would be like doubling G. The Earth would go into a new, much lower energy orbit. But if the force were the other way then yeah, we would pretty much just float off in a straight line. Rckrone (talk) 13:00, 30 September 2010 (UTC)[reply]

Why the "standard" in "standard gravitational parameter"?

The standard gravitational parameter $\mu$ of a celestial body is the product of the gravitational constant $G$ and the mass $M$ of the body,

\mu =GM.

Why is it called "standard" as if there were many other gravitational parameters for the body in question? —Bromskloss (talk) 09:33, 29 September 2010 (UTC)[reply]

There is also the Gaussian gravitational constant for a celestial body, which is just a different way of expressing µ. The "standard" in the name, implies that it is the parameter that is expressed in the simplest manner with regards to the International System of Quantities. Physchim62 (talk) 14:02, 29 September 2010 (UTC)[reply]

Thank you. I had never heard of that one. —Bromskloss (talk) 06:54, 30 September 2010 (UTC)[reply]

Peas and potatoes without fertiliser?

As a survivalist I plan to grow potatoes indoors in pots. If I grew them with peas in the same pot, would nitrogen fertiliser be required, since peas fix nitrogen from the atmosphere? Also, could a potato be genetically engineered to fix its own nitrogen? —Preceding unsigned comment added by 80.1.88.10 (talk) 13:55, 29 September 2010 (UTC)[reply]

Technically, it's a symbiotic bacterium that's fixing nitrogen, see Legume#Fixation_of_nitrogen_in_the_soil. Crop rotation is the traditional way to reap the rewards of this nitrogen. I don't think synchronous growing would work as well for this pairing, but see Companion_plants for more information on you idea. Genetic engineering of potatoes to form their own symbiosis whith rhizobia seems unlikely, though perhaps not impossible. Composting will also be important for you as an agrarian survivalist. SemanticMantis (talk) 15:04, 29 September 2010 (UTC)[reply]

I don't think it would work if you grew them with peas as opposed to after peas. The nitrogen is fixed in the Root nodules. Farmers normally get the extra benefit from the roots by leaving them in the ground and ploughing for the next crop. Because the nitrogen fixation comes from mutualism by way of a nodule, genetically engineering the bacteria to favour potatoes and engineer the potatoes to form nodules might be possible one day. But beware and remember that old Chinese proverb: “She who cooks potatoes and peas in the same pot, is being unhygienic”.--Aspro (talk) 15:05, 29 September 2010 (UTC)[reply]

Nice Chinese proverb. Any idea what it might be getting at? I like to add some potatoes to my split-pea soup...SemanticMantis (talk) 15:08, 29 September 2010 (UTC)[reply]

I have no idea what it means but it leads nicely to the next thing that every survivalist should recycle as a good rich source of plant usable nitrogen. Urine#Agriculture--Aspro (talk) 15:19, 29 September 2010 (UTC)[reply]

Isn't it just a pun on pea/pee? Incidentally, urine can be used as a satisfactory source of nitrogen, though the smell may be disagreeable if you're using it indoors. Buddy431 (talk) 16:09, 29 September 2010 (UTC)[reply]

As SemanticMantis says Crop rotation is the traditional way and there is more info in our article Organic farming. Too much nitrogen can be bad though for some crops including potatoes and carrots. [1]. --Aspro (talk) 15:35, 29 September 2010 (UTC)[reply]

RE genetic engineering - yes it should (hopefully) be possible one day. The genes involved in the formation of the symbiosis appear to have been "borrowed" from the much older mycorrhizal symbiosis between plants and fungi, which potatoes already have. Here's the most recent free review I can find. (We don't seem to have any discussion of the genes involved in mycorrhizal symbioses at the moment.) Oh and if you're growing plants indoors, light is going to be much more of a worry than nitrogen, and running high power lights isn't very survivalist, as AFAIK the only thing you can grow profitably indoors is illegal. Smartse (talk) 16:30, 29 September 2010 (UTC)[reply]

That is not true if you have a room with many windows or a greenhouse. Googlemeister (talk) 18:08, 29 September 2010 (UTC)[reply]

Touchscreens and finger damage

Is there any evidence it's unhealthy to use a touchscreen since you're pressing hard on to a solid wall over and over? There's also the friction of repeatedly dragging your fingers across glass. If it's not damaging then why do keyboards have springs in the firstplace? TheFutureAwaits (talk) 14:33, 29 September 2010 (UTC)[reply]

Keyboard keys are a normally open switches. The spring brakes contact again once your finger leaves it. There is no evidence as far as I know. Don't press so hard. If you were a farm labourer you would know what 'hard' was.--Aspro (talk) 14:40, 29 September 2010 (UTC)[reply]

Aspro has it. The friction is surely no risk, unless you count toughened skin or calluses as unhealthy. Potentially, if you pressed hard all day with the same finger, you could conceivably develop Repetitive_strain_injury that finger, but this is a stretch. Additionally, the spring-loaded keys give tactile feedback to the user, which has worked out pretty well. SemanticMantis (talk) 14:58, 29 September 2010 (UTC)[reply]

Keyboards have springs because they're made of buttons, and that's how buttons work. Without the springs (Or some similar mechanism) there would be nothing to hold the key 'up' (and therefore 'off') when you weren't pressing on them.

Touchscreens are much more technologically complicated. APL (talk) 16:41, 29 September 2010 (UTC)[reply]

I spend a lot of time typing on a keyboard and find sometimes even with that my fingertips can get a little sore, though not as much so as with the touch sensitive thing whose name I have now forgotten that my laptop has instead of a mouse. whilst perhaps not unhealthy, (though of that I am not qualified to say for certain), it can be a little uncomfortable after a while. 148.197.121.205 (talk) 14:54, 1 October 2010 (UTC)[reply]

Ferric nitrate pictures

Why does iron(III) nitrate have two different pictures with two different colors? Both of them say that they picture the nonahydrate. --Chemicalinterest (talk) 14:48, 29 September 2010 (UTC)[reply]

One of the picture captions is wrong. A variety of sources ([2], [3]) identify the nonahydrate as being a pale violet color, as shown in File:Watchglass2.jpg. The preparation of anhydrous ferric nitrate is a finicky process, and the product isn't very stable. The synthesis was described by D.J. Lovejoy and A.J. Vosper in 1968. They report that the anhydrous form is a "yellow-brown involatile solid" – perhaps something that looks like File:Iron(III)-nitrate-nonahydrate-sample.jpg, but I wouldn't count on it for the article – which slowly decomposes in air to form ferric oxide.

This paper describes thermal decomposition of the nonahydrate in still air. It is possible to cook off water to get the dihydrate, but not the fully anhydrous form. (Further heating of the dihydrate causes a decomposition to ferric hydroxide.) TenOfAllTrades(talk) 16:11, 29 September 2010 (UTC)[reply]

It does look like there is some oxides or hydroxides in the picture. --Chemicalinterest (talk) 17:33, 29 September 2010 (UTC)[reply]

I took the photo File:Iron(III)-nitrate-nonahydrate-sample.jpg. It was about 10 years old at the time I think! Maybe the pale violet colour is masked by the strong orange-red colour of oxide impurities.

I'll try and find some fresh stuff.

Ben (talk) 18:01, 30 September 2010 (UTC)[reply]

4 Fe(NO₃)₃ → 2 Fe₂O₃ + 12 NO₂ + 3 O₂ This might be a culprit. It spontaneously happens to nitric acid. Fe(III) might be acidic enough to make this reaction happen slowly too. --Chemicalinterest (talk) 21:06, 30 September 2010 (UTC)[reply]

peppers and blood

What effects would eating hot peppers have on a human's blood pressure? Googlemeister (talk) 15:49, 29 September 2010 (UTC)[reply]

By hot peppers, you are referring to capsaicin. This is a very complicated issue. Some studies have shown that capsaicin inhibits transition from non-hypertension to hypertension. Other studies have shown that increased capsaicin has caused temporary but drastic increases in hypertension. There are many studies in mice and dogs. One that I found interesting was application of capsaicin in the nostril (technically, deep in the nostril to the sinus cavity) and how it heavily correlated with an increase in blood pressure. So, you can certainly find a study that backs whatever view you want to have on the topic, but the overall answer is that the relationship between capsaicin and hypertension is complicated. -- kainaw ™ 15:56, 29 September 2010 (UTC)[reply]

After further research, I have found multiple studies in humans that indicate capsaicin interacts with hypertension medication as well - usually in a negative way. So, if a person is taking hypertension medication and consumes a large amount of capsaicin, there is a probability of lowered anti-hypertension effect from the medication. -- kainaw ™ 17:13, 29 September 2010 (UTC)[reply]

Oxidation of pyrogallol

I notice that the article about pyrogallol mentions the fact that it readily absorbs oxygen. It does not however give a balanced equation of the reaction. Does anyone know what the equation looks like so we can add it to the article. Obviously the first bit is C6 H3 (OH)3 + O2 ---> but what would the products be? Maybe water and something else? At any rate it should be added to the article. Anyone? Jay-Sebastos (talk) 19:26, 29 September 2010 (UTC)[reply]

The ring is very nucleophilic. The oxidation will lead to a benzoquinone like motif -- a Michael acceptor. Note that pyrogallol is very nucleophilic enol -- (an aromatic enol, but still an enol) -- so another pyrogallol molecule will then attack this Michael acceptor. This aldol addition reaction rearranges to form purpurogallin. [4] John Riemann Soong (talk) 19:39, 29 September 2010 (UTC)[reply]

Ben (talk) 20:08, 29 September 2010 (UTC)[reply]

Thanks a lot for the help. Yes this would make sense. We should probably add this to the article about pyrogallol as well. Jay-Sebastos (talk) 20:16, 29 September 2010 (UTC)[reply]

Oscar question

I bought two 1.5 inch oscars the other day and now my parasitic snails (which I enjoy in my tank) are gone -- I had counted about 30 of them, and I can find 2 now. How can the oscar eat the snails with their snails? There's no way 25 shells can fit in his guy and how is he going to digest the shells? DRosenbach ^{(Talk | Contribs)} 20:32, 29 September 2010 (UTC)[reply]

If they eat crayfish, as Oscar_(fish)#Feeding suggests, then I can't see they'd have much of a problem with snails. The first link on this google search says "For a start, Oscars eat snails in the wild, so periodically your captive Oscar may eat snails, knocking back the snail population." Which would seem to be your problem. Or rather, your ex-snails problem :( --Tagishsimon (talk) 21:20, 29 September 2010 (UTC)[reply]

Brackets

No, you can consider the expression in the middle, |B><C| as an operator. It projects a ket on |C> and then rotates it in the direction of |B>. If the identity you propose were to hold, then this operator would be proportional to the identity operator, which is clearly false. Count Iblis (talk) 23:15, 29 September 2010 (UTC)[reply]

Alright, does this change if B = C? 74.15.136.172 (talk) 00:17, 30 September 2010 (UTC)[reply]

If you put |B> = |C>, then you still have that |B><B| is proportional to a projection operator that projects onto the one dimensional subspace spanned by |B>, while on the right hand side of your proposed identity, you have the scalar <B|B> inside the braket, which you can replace by the identity operator times <B|B>. So, the identity still doesn't hold in that case. Count Iblis (talk) 01:05, 30 September 2010 (UTC)[reply]

The identity will hold only if B=D. 174.58.107.143 (talk) 06:14, 2 October 2010 (UTC)[reply]

Smell Illusion

If I sniff a strong smell or odour, could it distort the subjective smell of other odours afterwards? I'm wondering if there could be an analogy with colour, as looking at one colour can in some circumstances distort the perception of other colours seen aftwards or adjacently. Thanks. 92.24.190.229 (talk) 23:13, 29 September 2010 (UTC)[reply]

Yes it can. I don't know that there are distinct parallels with colour theory, but aroma is the major component of what we think of as flavour. Adding or removing aromas from a dish changes its flavour significantly. E.g. Ferran Adria's 2003 dish involving pan-fried shrimp served with a sprog of rosemary for sniffing while eating. You could also look to the world of perfumes; professionals in the industry sniff coffee beans to 'reset' their noses. Inhaling strong aromas will distort how weaker aromas smell after, as well. → ROUX ₪ 23:20, 29 September 2010 (UTC)[reply]

The effect with odors is actually much stronger than with colors, because the response to a strong odor adapts much more rapidly than the response to a given color. Sniffing a strong odor can even distort subsequent perception of the very same odor, because the responses to the dominant components can adapt out and allow weaker components to become noticeable. We have an article, olfactory fatigue, relating to this, but it isn't very informative. Looie496 (talk) 00:39, 30 September 2010 (UTC)[reply]

Almost all the perfume shops that I have visited had coffee beans kept in bowl for customers to sniff to restore their smelling sense after smelling any perfume. - manya (talk) 03:51, 30 September 2010 (UTC)[reply]

Animal memory

Other than elephants, what animals are associated with having a good memory? —Preceding unsigned comment added by Procrastinatus (talk • contribs) 23:57, 29 September 2010 (UTC)[reply]

After humans check out Animal_cognition#Memory. hydnjo (talk) 00:41, 30 September 2010 (UTC)[reply]

I'm not sure the extraordinary memory of elephants has been scientifically demonstrated. Anyway, leaving them out, there is no animal species with a memory for specific events comparable to that of a human, but there are some species that have good memory in particular domains. As the already-mentioned animal cognition article mentions, some birds and rodents are capable of remembering the locations of hundreds of hidden food caches. Also, primates behave as though they can remember large numbers of social encounters. Looie496 (talk) 00:54, 30 September 2010 (UTC)[reply]

I saw a documentary that claimed elephant matriarchs remember the locations of watering holes that they haven't visited in many years (FWIW). Clarityfiend (talk) 02:08, 30 September 2010 (UTC)[reply]

Check out Rico (dog). Robinh (talk) 08:05, 30 September 2010 (UTC)[reply]

Memory is a very tricky thing. What humans call memory is really a whole set of things related to information recall, synthesis, learning, and so forth, aside from the different categories of long term, short term, etc. Squirrels are a classic example: they are not very bright by most other standards (for a mammal) but can remember where they have hidden hundreds of nuts a year previous.[5] It's not clear that this kind of specialized memory is the same thing one should compare human memory to, for example. --Mr.98 (talk) 13:24, 30 September 2010 (UTC)[reply]

Pigeons trained in a Skinner box to do an operant discrimination task when they were very young were maintained in cages without further Skinner box experience until they were quite elderly. When placed in the Skinner box, they immediately resumed skilled operant behavior. The did not forget the training. Edison (talk) 04:31, 1 October 2010 (UTC)[reply]

Octopi are supposed to be good at learning stuff, there was one that was trained to open jars. Presumably it would be difficult to acquire a skill like that if the animal promptly forgot it every time. then, of course, there is the one that can remember stuff that hasn't happened yet. 148.197.121.205 (talk) 14:48, 1 October 2010 (UTC)[reply]