Wikipedia:Reference desk/Archives/Science/2013 July 8

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July 8

Angular Momentum

Our earth revolves around its axis, likewise all other planets do the same. All planets and asteroids rotate around the sun which in turn rotates around its axis. Our solar system is a part of the Galaxy which rotates around its center. All other galaxies do likewise. This angular momentum (of our galaxy) could only come from the angular momentum of the primordial hydrogen gas that gave it the mass. Where did this angular momentum come from?

Is it possible to speak of the angular momentum of the whole Universe? If so then the Universe could not be infinite. Correct?

When two galaxies collide, is it possible to assume that they may have vectors of their angular momenta pointing in different directions, perhaps in the opposite directions? Where did this difference come from? How come that after the big bang different parts of the cosmos acquired different angular momenta?

Is there any coherent theory that describes it?

Thanks, - Alex174.52.14.15 (talk) 03:54, 8 July 2013 (UTC)

How do you know the net angular momentum of the universe is not zero? That is, that for every object spinning in one direction at a given speed, there isn't an object spinning the other way? --Jayron32 03:58, 8 July 2013 (UTC)

Absolute rotation and Mach's principle deal with the problems of ascertaining rotation in a large and possibly infinite universe. The other questions - how did the different parts of the universe evolve such that some parts rotate around other parts... well, the universe is not currently homogeneous - mass, energy, and momentum are not uniformly distributed when we consider any relevant scale of length and time. On the scales of galaxies and stellar systems, we can describe how initial conditions are most likely to evolve toward the (almost) steady state we see today, using statistical mechanics, and we see that flattened, coplanar orbits are a low energy configuration that is very likely to evolve, if the initial distribution of matter and energy and momentum started inhomogeneously. Either this distribution was always inhomogeneous (and has evolved to its present state from an initial condition); or the universe started homogeneously and was subjected to some type of spontaneous symmetry breaking in the very early universe. We don't yet know which possibility is more plausible; but high energy research has investigated the nature of symmetry breaking to see if that sort of theory is viable. Nimur (talk) 04:21, 8 July 2013 (UTC)

(ec) This is really a variation on the question of why matter isn't evenly distributed throughout the universe. Once you have clumps of matter, then inevitably those clumps will start to spin as they collapse into smaller, denser clumps. The exact direction they will start to spin depends on the precise distribution of the clumps. StuRat (talk) 04:25, 8 July 2013 (UTC)

To add a fact I learnt recently, which may complicate the issue a litte - rotation around a black hole is (sometimes?) not caused by Newtonian forces, but by spacetime itself curving around the black hole. Aaadddaaammm (talk) 09:50, 8 July 2013 (UTC)

Angular momentum is conserved but that doesn't mean that a non-rotating primordial cloud can't produce spinning planets, suns and galaxies. Suppose you take two objects, each moving toward the other in a straight line with no rotation whatever - then, suppose that they collide off-center. They will both start to spin...and in a frictionless, dragless environment, they'll continue to spin as they move away from each other. Angular momentum is conserved because they each rotate in the opposite direction such that the total angular momentum is still zero. But examine one of these objects when it's drifted thousands of lightyears from the point of collision - and you'll see it spinning all by itself - not noticing that the exact opposite spin is present in some other incredibly distant object.

Hence, it's perfectly reasonable to presume that at the instant of the big bang, nothing whatever was rotating and that the net angular momentum was zero. If that's the case, then despite innumerable collisions and other interactions setting things spinning, the total angular momentum of the entire universe could still be zero. But that's one of those things that we don't yet know. SteveBaker (talk) 13:03, 8 July 2013 (UTC)

Inflation explains why it is zero.Count Iblis (talk) 13:33, 8 July 2013 (UTC)

Where in Wikipedia can I read about rotational anisotropy amongst distant galaxies? Anisotropy#Physics says: "Cosmic anisotropy has also been seen in the alignment of galaxies' rotation axes and polarisation angles of quasars." but doesn't go into any detail. -- 177.121.216.128 (talk) 14:08, 8 July 2013 (UTC)

How about The Observational Approach to Cosmology, by none other than Edwin Hubble, available for free online in its entirety thanks to Caltech and the Mount Wilson Observatory. This was written in 1937 - Hubble relied exclusively on observations in visible light; so there is no mention of radio astronomy in any way; but, from visible light observation alone (including spectrometry), Hubble could deduce the fundamental nature of our expanding universe. There is a few sections in there about inhomogeneous distribution of matter. But for the most part, in visible light, all galaxies are uniformly distributed and randomly aligned. Any anisotropic effect must be very small!

Of course, the cosmic microwave background radiation was not discovered until radio astronomy became commonplace, a few decades later. Often, when cosmologists talk about anisotropy, what they mean is that they are inferring anisotropy from the inhomogeneity of the CMB. In principle, you can infer anisotropy from any non-uniform distribution of stuff in the universe; but the CMB makes the job easier because it is an imprint of such an early stage of the universe.

The only scientists who (attempt to) measure anisotropy directly must do so in laboratory conditions: in particle colliders, or spectrometry experiments, or in applications of material science. The cosmos is too large to see anisotropy (in controlled experimental conditions); it must be inferred by concocting cosmic-scale laws of physics that are consistent with our other observation. Nimur (talk) 16:37, 8 July 2013 (UTC)

Thank you all. It is very interesting. - Alex174.52.14.15 (talk) 23:39, 8 July 2013 (UTC)

clam nectar

Why doesn't lobster nectar or crab nectar exist?Curb Chain (talk) 06:26, 8 July 2013 (UTC)

Nectar comes from plants. Perhaps that's why? (unsigned: 09:25, 8 July 2013‎ User:Zzubnik)

Clam nectar is a thing, but is not nectar in the normal sense. You cook clams, pour off the clam broth, concentrate it by evaporation, and what you have is called clam nectar Read more (barely) at Clam liquor. From looking on Google, it is readily apparent that lobster and crab broth are used in plenty of recipes. No clue why no one concentrates it to nectar. Although I don't know why anyone would want to. Or maybe they do but they just don't call it that. Someguy1221 (talk) 10:26, 8 July 2013 (UTC)

Thanks for the clarification, Someguy12212 Zzubnik (talk) 12:17, 8 July 2013 (UTC)

Clam nectar doesn't come from plants. I imagine that you could easily make lobster of crab nectar, but even clam nectar doesn't seem to be such a popular product, maybe there's not so much demand for other fishy nectars? Aaadddaaammm (talk) 09:48, 8 July 2013 (UTC)

There's clamato juice. Rmhermen (talk) 17:17, 8 July 2013 (UTC)

Fonds made from lobster or crab are a standard ingredient in fine cooking, especially for seafood recipes. In German, this is called Hummerfond or Krustentierfond, but I cannot find the corresponding English term. --Stephan Schulz (talk) 11:15, 8 July 2013 (UTC)

I believe it would be a lobster or crab bisque. --TammyMoet (talk) 18:38, 8 July 2013 (UTC)

What about oyster liquor? It is not cooked; it is the liquid found when the oyster is open live (Am I correct that the oyster is still alive when it is opened?). Do clams have the same sort of liquid?Curb Chain (talk) 00:31, 9 July 2013 (UTC)

They do, when you eat them similarly. --Jayron32 00:09, 10 July 2013 (UTC)

Technical terms for snap-together fastening mechanism?

In many products, two halves of the enclosure are snapped together. In one of the halves, there are tabs with a raised part, sometimes with a profile of half an arrow head if viewed from the side. In matching places in the other half of the enclosure, there are indentations or slots that catch the raised parts of the tabs.

Is there a technical term for this type of fastening mechanism? Are there technical terms for the tabs, the raised part of a tab, and the indentations/slots?

Thanks. --98.114.146.200 (talk) 10:13, 8 July 2013 (UTC)

Sounds like some type of snap fastener. Can you link to an example or illustration?--Shantavira|^{feed me} 10:43, 8 July 2013 (UTC)

I think we're talking about the plastic tabs that would hold together the two halves of the cover of a device like a cellphone or something like that. I guess I'd call it a "self-locking tab", a "clip", a "snap" or just a "captive fastener" - I'm not aware of any more specific term and a search through the long list of articles referenced from fastener didn't turn up anything useful. The tool for opening such fasteners is called a "spudger". A Google search on that term produced lots of pictures of these kinds of fastener - but I didn't see any kind of consensus on the name. So it's possible that there is some obscure technical term - but nothing that seems to be in widespread usage. SteveBaker (talk) 12:50, 8 July 2013 (UTC)

Snap Fit - manya (talk) 05:05, 9 July 2013 (UTC)

Yeah - could be. The two pictures at right are titled that way - but there are no English language Wikipedia pages pointing to either of them. I think we need an article about these things - and a link to it from fastener. SteveBaker (talk) 17:11, 9 July 2013 (UTC)

What is the function of women having longer hairs?

Is this trait present in other primates, too? — Preceding unsigned comment added by 128.237.205.60 (talk • contribs) 13:58, 8 July 2013‎

It's fashion, not biologically determined - humans choose their own hair length. Roger (Dodger67) (talk) 14:06, 8 July 2013 (UTC)

Really? Do women's hair grow faster or there are no difference?

There are no sex-based differences at hair growth, nor have I ever heard of such a claim. Indeed, fashion and personal choice seem to be the rule, e.g. Fabio Lanzoni, pixie cut, etc. SemanticMantis (talk) 14:40, 8 July 2013 (UTC)

I do not believe women's hair grows faster. Anyway, the question should be why men have short hair? If men are warriors, then short hair is an advantage. You don't have to take care of it in the battle field, no one can grab you by the hairs in a fight, any injure can be cleaned more thoroughly. It's not only fashion, but there is also a social role here. OsmanRF34 (talk) 14:42, 8 July 2013 (UTC)

Also gets quite hot, obstructs your view and can cut or choke you in some grappling positions. Even in the milder context of mixed martial arts (with its rules against hair-pulling and a shower after twenty minutes) a (near) bald head or cornrows is the way to go. Benson Henderson is a notable exception, but even he gets distracted by it in his face lately. InedibleHulk (talk) 22:56, 9 July 2013 (UTC)

Speaking from personal experience, it takes 2 to 3 years to grow my hair to my shoulder blades and then it stops. (I'm a man.) An ex girlfriend was a hair factory. She would get her waist length hair cut at the start of the summer (usually usually the week before Christmas) and by the time Autumn arrived, it was waist length again. She used to sell it to wig makers. Short hair is a definite advantage in trench warfare; it's very hard to keep your hair clean in the mud. --TrogWoolley (talk) 15:28, 8 July 2013 (UTC)

My hair (male) will grow to my shoulders in about 6 months (though I haven't let it get that way for quite a while! It goes from about a half inch to enough fringe to enough to get in my eyes in around a month now). It stopped about half way between shoulder and waist (once strightened, it's rather curly). Hair growth varies a lot in both genders! MChesterMC (talk) 15:38, 8 July 2013 (UTC)

Here's a story about a Vietnamese, who died 3 years ago, whose hair was over 18 feet long.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:42, 9 July 2013 (UTC)

Note the Roundheads were a recent misfortune of history - for some reason many ancient warrior cultures didn't find it a problem; not sure if it was a matter of how they wore it or just that given a few minutes before an axe bites into the back of your head there is something better you could be doing with your life than pulling somebody's hair. Wnt (talk) 06:03, 9 July 2013 (UTC)

There are plenty of cultures, even today, where men keep long hair. Sikhs are one example (see [2]), although most modern Sikhs keep their hair short. The Tibetan people are another example: see [3]. In ancient China, hair was seen as a gift from one's parents and therefore never cut; only criminals had their hair cut as punishment. (The Manchu people, after deposing the Ming dynasty, forced all men to adopt the queue (hairstyle) or be beheaded.) See long hair for many more examples of both modern and historical men who had long hair. --Bowlhover (talk) 08:04, 9 July 2013 (UTC)

If long hair was problematic, beards might be worse. It might be that many men go bald as they get older while women generally don't. Ancient Greeks seemed to have beards, Romans less so, St. Paul opposed long hair on men, while Nazarites--like Sampson--didn't cut theirs. Custer seemed to have it long, but by soldiers had it short (very short at times).174.137.237.65 (talk) 19:39, 11 July 2013 (UTC)

Why is pseudoscience so popular?

Despite the fact that we're in the Information age and it's so easy for one to lookup what actual scientists have to say about the latest pseudoscientific theory, people are still easily fooled into Pseudoscience. 163.202.48.125 (talk) 14:20, 8 July 2013 (UTC)

Because people want easy explanations, not difficult science? WegianWarrior (talk) 14:24, 8 July 2013 (UTC)

coming up with hypotheses is easy. coming up with hypotheses which are correct is hard. coming up with hypotheses which are correct, and proving them, is hard and involves actual work. thus, reduction in popularity from one to the next. Gzuckier (talk) 15:12, 8 July 2013 (UTC)

It's because the educational system focusses much more on subjects like language, history, art than on science. We insist that our children learn about history, even if they don't need to know anything about this subject for their future jobs. We can't bear the idea that the future generation would know little about, say, the US war of independence. However, we have accepted the fact that a large fraction fo the population doesn't know anything about Newton's laws of classical mechanics, that they don't know much about mathematics that even people in ancient Greece knew about. Modern science is then not something people can readily understand, it has to be explained in a dumbed down way to them, it can then be difficult for people to see the difference between real science and pseudoscience. Count Iblis (talk) 15:27, 8 July 2013 (UTC)

We would like our children to know about other languages, other cultures, history, philiosophy, music, literature and art as well as science, logic, mathematics and how to rewire a plug and unblock a drain so that they grow up to be well rounded individuals with a variety of resources to draw on in whatever life situations they find themselves. The more knowledge you have in any and all fields, the more ability you have to critically assess the claims of others and, in the end, to reach your own reasoned and reasonable conclusions. Gandalf61 (talk) 16:08, 8 July 2013 (UTC)

Yes, but the criticism of many physicists has been that physics as is it taught in school, is totally misleading. It gives children a wrong view of what the subject is about, most of what is known about how the Universe works is not taught at all. For most other subjects this is not the case, e.g. you do learn in biology class about modern biology. Critical thinking alone is not sufficient, you have to have some minimum amount of basic knowledge. E.g. children in school are not told about the very strong limits on any new forces and how these limits are obtained. There is no reason why you first have to master quantum field theory at university before you can be even told about the basics of the argument. This means that a huge fraction of the population will be unaware fo this, which leaves a lot of room to promote all sorts of pseudoscientific nonsense. Count Iblis (talk) 17:39, 8 July 2013 (UTC)

I don't think it's just physics that has that issue. If you take high school chemistry at face value, you'd think all chemists do is unit conversions. Are moles important? sure, but so are lots of other concepts that don't get mentioned at all. (+)H₃N-Protein\Chemist-CO₂(-) 18:45, 8 July 2013 (UTC)

Right, because teaching children who lack the proper training in the basics things like advanced quantum theory and general relativity is likely to generate positive results. One thing experts forget is that children are not experts, and need to receive basic instruction before they receive advanced instruction. You don't start learning French by reading Molière on the first day, and you don't learn physics and chemistry by starting with the most advanced subjects. You start with the language of chemistry and the language of physics, and build up to the more advanced subjects. --Jayron32 23:12, 8 July 2013 (UTC)

It also doesn't help that the reporting of actual science isn't anything to write home about either. I had a paper published earlier in the year that got a fair amount of mention in the press here in the UK. The BBC website and the broadsheets did a decent job, but the tabloids just ran with it until I even barely recognised it as something I did..... If actual science is not always reported accurately, how the hell is the lay public supposed to know what's genuine and what's not? Fgf10 (talk) 18:54, 8 July 2013 (UTC)

One problem is the lack of critical thinking skills in the general population - these are not taught in schools or even at college level most of the time. It's not even necessary to have much of a science training to get the benefit from that skill set. Just a willingness to stop and think about whether the claims that are being made are likely to be true or not.

Today I read a UFO-nut claiming that Roswell is at 33 latitude, 104 longitude and that the aliens landed there because it's the only dry-land place in the northern hemisphere for which latitude multiplied by pi equals longitude. Math and science let's me know that there must be an infinite number of points on a path for which this is true...but critical thinking makes you ask "Why would the aliens measure latitude from Greenwich?"...and "They rounded to the nearest degree? That's like 60 miles!"

Another problem is that too many people seem to adopt the attitude that if they wish that something were true, then it must be true. "I wish that I could live forever...so there must be an after-life." - that kind of thing.

These problems don't just affect pseudo-science belief - it runs through everything from gambling to buying an extended warranty on your new DVD player to purchasing junk advertised for $19.99 on TV. None of these activities withstands the test of critical thinking.

SteveBaker (talk) 19:54, 8 July 2013 (UTC)

Indeed, some people can reject something that has a huge amount of supportive evidence, like AIDS, intelligent design, or evolution, but embrace any topic in the List of topics characterized as pseudoscience. Hint: just believing in scientist won't make you avoid pseudoscience, you'll still have to check evidence by yourself. Obviously, you won't be able to dedicate much time at each topic, so, you are left with the alternative of trusting other people. No one can avoid being wrong at the end of the day. Time will prove this right. OsmanRF34 (talk) 23:15, 8 July 2013 (UTC)

Did you make a slight error with "has a huge amount of supportive evidence, like AIDS, intelligent design, or evolution, but embrace any topic in the List of topics characterized as pseudoscience" because as I suspected intelligent design is listed as pseudoscience. CambridgeBayWeather (talk) 06:50, 9 July 2013 (UTC)

Sure, thanks for pointing that out. The evidence if for evolution (vs. intelligent design with little evidence, besides look at how complex we are). OsmanRF34 (talk) 07:27, 9 July 2013 (UTC)

The media is generally useless in properly covering scientific matters. Ever known a sciency, nerdy kid at school choose to be a journalist? Too many leading politicians are scientific ignoramuses. Those who support those politicians' parties are psychology pressured to go along with their positions. That's a lot of people. (But I still find it hard to believe that all Republicans in the US were as bad at science as their most recent President. How COULD they accpet that?) HiLo48 (talk) 23:38, 8 July 2013 (UTC)

This being what's called the "Reference Desk", are there any references we could give the OP (rather than our own personal theories)? -- Jack of Oz ^[Talk] 23:55, 8 July 2013 (UTC)

Maybe the OP could first give us a reference for why he said what he said. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:31, 9 July 2013 (UTC)

People tend to believe things that are pleasant to believe, rather than things that are supported by careful evidence. See appeal to consequences, wishful thinking, valence effect and optimism bias. Red Act (talk) 01:46, 9 July 2013 (UTC)

It wasn't that long ago that continental drift would have been considered pseudoscience. Also, I'm not sure why conspiracy theories would be considered "pleasant", although maybe it is pleasant for the believers, as it gives them a false sense of empowerment. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:47, 9 July 2013 (UTC)

And it's funny the OP would bring this up on a day that Google marks as the 66th anniversary of the alleged incident at Roswell. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:49, 9 July 2013 (UTC)

There is fundamental challenge in educating people about science and critical thinking i.e. there is limit to knowledge but there is no limit to ignorance. - manya (talk) 04:51, 9 July 2013 (UTC)

That is exactly wrong. μηδείς (talk)

What do you mean by 'exactly'? There is no limit to knowledge? Or, limit (gaps in knowledge) is not a fundamental issue? Ignorance is not a reason at all or it it not the root cause? - manya (talk) 04:48, 10 July 2013 (UTC)

Medis is correct - there is a definite limit to ignorance and no limit whatever to knowledge. The limit to ignorance is knowing nothing whatever. Someone with literally no knowledge at all is at "absolute zero" on that scale. On the other hand, there are an infinite number of facts you can potentially learn - for example, you may know that (2^57,885,161−1) is a prime number - but there are an infinite number of primes that you can still learn about. Of course in practical terms, there is a limit to how much one human can learn - there are only so many neurones in your skull with which to store that information - but there isn't a limit on the number of things that are out there to be learned. SteveBaker (talk) 19:27, 10 July 2013 (UTC)

Yes, Steve has explained my meaning. A dead dog and a log are both equally ignorant, at a coefficient of zero. Of course, infinite ignorance is a good turn of words when it is called for! μηδείς (talk) 01:39, 11 July 2013 (UTC)

Alright, let me try to explain what I meant to say. We are talking with reference to OP's question as to why people are fooled and why don't they look up available information. This is not about fortunate people who get right guidance from scientists or from educated people with scientific views. Modern science theories and knowledge associated with it was just not there few hundred years back. Few decades from now there will be more knowledge/information. There is limit to such knowledge. (Knowing what prime is knowledge, knowing how to find prime is knowledge, but knowing millions of primes is not the knowledge in this context). And pseudoscience begins where science ends. For example, when knowledge about lightning was not there, it was obviously act of God/daemon. Don't look at ignorance as a measure of lack of knowledge. It is an attitude that one has developed due to which one refuses or denies factual knowledge. For many, it is simpler and easier to believe that 'God made big bang' and life has been "created". - manya (talk) 09:11, 11 July 2013 (UTC)

For something to read other than just our opinions, you could try pseudoscience#explanations. You could also read How Mumbo Jumbo Conquered the World by Francis Wheen. This last one doesn't really explain a lot, but it goes into a lot of information about how these things take off, historically speaking. IBE (talk) 09:36, 10 July 2013 (UTC)

One factor is entertainment. For example, the "Bermuda Triangle" has been thoroughly debunked, but for some folks it's more fun to believe in it (on some level) than to not believe in it (on any level). ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:28, 10 July 2013 (UTC)

I'm going to be brave and mention religion. It's obvious that some people get their facts from their preachers. If you choose to trust them, and lots of people do, you choose to accept everything they say. That can be very misleading. HiLo48 (talk) 11:31, 10 July 2013 (UTC)

Religion is not a pseudoscience, it's a cultural phenomenon, like language and clothing style and so on. I've known religious folks who were also totally accepting of the scientific method. And I've known atheists who thoroughly believe in the Bermuda Triangle, flying saucers, and that we didn't really go to the moon. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:36, 10 July 2013 (UTC)

Religion isn't considered a pseudoscience because it's not falsifiable - not because it's a cultural phenomenon. Religious belief is on the decline worldwide (See Demographics of atheism) while, in Pseudoscience#Demographics, we hear that "The National Science Foundation stated that pseudoscientific beliefs in the U.S. became more widespread during the 1990s, peaked near 2001, and declined slightly since with pseudoscientific beliefs remaining common.". If the numbers in Demographics of atheism are to be believed, the number of religious believers peaked sometime around 2008 and is now also in decline. This is a weak correlation - but it's plausible that many people lose their belief in various pseudosciences, then realize that their religious belief is more of the same kind of thing and give that up too. But the conclusion that belief in religion and belief in pseudoscience are related is not an insubstantial one.

SteveBaker (talk) 19:27, 10 July 2013 (UTC)

Bugs and Steve - you both missed my point. Maybe I didn't express it well. I wasn't suggesting that religion itself is a pseudo-science. Even in my country there are people so hooked on their religion that they trust their pastor for all knowledge. That means they believe in Creationism (a pseudo-science in my book), and all its associated nonsense, such as an earth that was created in 4000 and something BC. That means they can't believe what their science teachers tell them on evolution. Once that seed is sown, they have less trust in what their science teachers are telling them about anything. HiLo48 (talk) 22:17, 10 July 2013 (UTC)

Yes, I think that's a definite issue here. Creationism is basically a totally debunked pseudoscience - although it's possible to formulate a statement of it that's unfalsifiable - for example, if you maintained that the creator created everything 4,000 years ago - you might claim that he/she/it deliberately included things like fossils and long stretches of identical DNA in wildly disparate lifeforms and strong indicators of evolution such as the recurrent laryngeal nerve in the giraffe. If the creator does a perfect job of creating a universe that looks EXACTLY like one that began with the big bang and included Darwinian evolution - then indeed the world could be 4,000 years old. However, creationists that I've spoken to don't seem to believe that - they prefer to believe that dinosaurs had bones made from solid rock and that they died and sank deeply into the mud during the Noah's flood because they were so heavy. (sigh!) SteveBaker (talk) 14:29, 11 July 2013 (UTC)

Secondary cells/rechargeable batteries

I am doing a science project on batteries, how it works, the effects on the environment as well as rechargeable batteries. I've searched the web and took out all 4 chemistry books at our local library, but I can't find any useful info on rechargeable batteries. All I could find was the discharge rates, history and so forth.
I am doing a few experiments: building normal batteries with combinations of

• Zink,Zinc sulphate
• Iron, Iron Sulphate
• Copper, Copper Sulphate
• Magnesium, Magnesium Sulphate
  

,meaning that I could build a total of six batteries. I did these already and it worked fine, but now I want to build a rechargeable cell. Can I use one of these combinations to recharge with a DC current? (And then how large must the current be?)
Can someone please help me, I really did my best to do it on my own?
Thanks!
--Romeo Kilo (talk) 15:48, 8 July 2013 (UTC)

It sounds as if you are wanting to build a Nickel–iron battery and a Lead–acid battery. Please note that both contain corrosive electrolytes, so great care should be taken with these. Dbfirs 15:55, 8 July 2013 (UTC)

Part of (some would say the main) goal of a science fair is to develop and test your own ideas, not just reproduce what someone else has already done. You wonder "what if?" or "would this work?", based on "well, it goes one way, can I push it backwards?" or "why aren't the same ones used for rechargeables?", and then you actually do the test. It's rare that students actually do that (instead just doing the "known" experiments over and over again), and it's refreshing to see that when I judge them. Maybe it will work! Maybe it won't! Maybe it won't work well but it will work "well enough" to prove that the idea is valid (and then the "extensions/future work" part of your conclusions is to improve them by varying electrode shapes, electrolyte concentrations, etc.; or to apply this really simple idea as a low-cost or chemically safer alternative for situations where that is a critical detail). DMacks (talk) 16:28, 8 July 2013 (UTC)

I agree with that, but there's a lot to be said for replicating previous results before trying to do something new. It's always a useful learning experience, and people who skip that step often end up regretting it. Looie496 (talk) 17:19, 8 July 2013 (UTC)

It is nice to have an opinion from a experienced judge! My teacher also prefers new and creative topics. The problem is, I am, according to a psychologist totally left-brained, so it is very difficult for me to think up my own ideas. I like science projects where there is a given topic, but when it comes to choosing your own topic...

Romeo Kilo (talk) 19:22, 8 July 2013 (UTC)

Another thing that I worry about is the fact that the reading on the voltmeter jumps around when the battery is connected. Is this normal? Should I take an average of the readings?Romeo Kilo (talk) 19:27, 8 July 2013 (UTC)

Investigating this would actually be a useful part of your project. How does the reading "jump around" (ie, how does it vary with time, approximately)? What factors do you think might cause this? How many of these factors can you eliminate or hold constant? Can you vary any of them, and see what influence they have on the voltmeter reading? Tevildo (talk) 01:28, 9 July 2013 (UTC)

I did this experiment myself in high school. My results were that none of what you have can make a rechargeable battery. But lead plates were rechargeable, and you did not have to use corrosive sulfuric acid for this to work either. Using exotic electrolytes like mercuric chloride had no useful effect. My highest current was with an aluminium pie plate in sodium carbonate solution, which could make one amp (with a carbon rod other electrode). There were amazing results with two aluminium electrodes and a carbon rod, it ended up working like a transistor. Graeme Bartlett (talk) 11:52, 9 July 2013 (UTC)

Wow, these are nice answers! – b_jonas 22:51, 10 July 2013 (UTC)

I got a new idea: I'm going to test if the concentrations of the salts used in the battery makes a difference to the volts. I'm sure it had been done before, but I could get no facts, so I am going to try myself. One concept I am struggling to understand is mol. Does anybody have a website, link or perhaps their own explanation of what mol is and how to use it? Thanks! (and sorry for my bad English)
Romeo Kilo (talk) 18:48, 11 July 2013 (UTC)

Is it true that fasting "programs" your body to store fat?

Topic says it all. ScienceApe (talk) 15:51, 8 July 2013 (UTC)

What? Could you please explain what you mean?Rich (talk) 05:36, 10 July 2013 (UTC)

This article from the Guardian discusses possible benefits of fasting, including weight loss, and less hospital time (according to several linked scientific studies) [4]. There was also a recent piece on NPR about the possible benefits of fasting, here [5]. Also, don't confuse planned, regulated fasting with so-called Yo-yo_effect which describes how certain "feast or famine" approaches to diet are linked to promoting fat storage (see article for refs). In short, fasting and yo-yo effect are rather different things. SemanticMantis (talk) 16:34, 8 July 2013 (UTC)

Fasting has been discussed here ad nauseam, you might want to search the archives at the top of the page. μηδείς (talk) 17:11, 8 July 2013 (UTC)

Also check Starvation response. Your body doesn't know if it's not getting any food due to your spiritual practices or a famine. It has learned to deal as well as it can with the latter, but it's badly programmed in the case of the former. OsmanRF34 (talk) 22:47, 8 July 2013 (UTC)

Hmmmm. I'm not sure your body doesn't know. Problem is, I can't think of a way to do an ethical controlled experiment to test that, so I'm not sure how to look up the result. It is certainly plausible that the body could have actual access to the knowledge of whether a fast was intentional or not. Wnt (talk) 21:45, 10 July 2013 (UTC)