Wikipedia:Reference desk/Archives/Science/2014 February 13

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February 13

how to know if you r pregnant

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This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

Chances are that you are not pregnant, if you happen to be male. StuRat (talk) 03:13, 13 February 2014 (UTC)

And if your parents never had any children, chances are you won't either. -- Jack of Oz ^{[pleasantries]} 07:17, 13 February 2014 (UTC)

Adoptees around the world will be rather disappointed to hear that. StuRat (talk) 17:26, 14 February 2014 (UTC)

Spoilsport. -- Jack of Oz ^{[pleasantries]} 18:53, 14 February 2014 (UTC)

Why do humans like rocking or swinging

I don't mean just autistic people, but all humans in general (we swing babies, swing on playground swings, and rock on chairs). I suppose autism exacerbates the feeling somehow, and so they do it more often. But I what to know what happens inside a normal brain that makes us feel different. OsmanRF34 (talk) 02:25, 13 February 2014 (UTC)

Music and dancing are very important parts of human culture. I guess that rhythm is somehow fundamental to how our monkeybrains work. Do other species seem to be slaves to the rhythm? Greglocock (talk) 02:48, 13 February 2014 (UTC)

It probably goes back to being in the womb, where the rocking would be the mother moving around. So, in times of stress, rocking can remind them of that time of safety. StuRat (talk) 03:15, 13 February 2014 (UTC)

Got a source for that random idea? Shadowjams (talk) 05:24, 13 February 2014 (UTC)

The term I found on pubmed is "spontaneous social rocking", and there's a suggestion that autistic children do it more than do other children.[1] It's easy to confound a lot of different things going on here though. Some aspects of rhythm have evolutionary roots, obviously across the animal kingdom, but also in humans (this one's especially on point).

There's a lot of related literature on music and the obvious importance of rhythm. That's a huge subject on its own with a lot of theories about why it happens. There's discussion of this in evolutionary musicology. This one too.

I'm having trouble quickly finding things specifically about physical rocking though. This seems (I don't have access to the full article) to suggest there's some primitive neurological basis to perform/enjoy rhythmic movements, at least I think that's its claim. Shadowjams (talk) 05:24, 13 February 2014 (UTC)

If I remember correctly, this topic is covered in an excellent book on human brain development titled "What's Going On In There?". 12.217.87.18 (talk) 14:28, 13 February 2014 (UTC)

I'm not sure if our article, Stereotypy, is related. Alansplodge (talk) 18:57, 13 February 2014 (UTC)

How Can the Oldest Star Yet Found Be Only 6,000 Light Years Away?

Yesterday, scientists in Australia announced that they had identified the oldest star yet found, SMSS J031300.36-670839.3. It is in the Milky Way, approximately 6,000 light years away. It is about 13.6 billion years old.

If we are seeing light that is only 6,000 years old, how can it have come from this star, which is supposedly 13.6 billion years old? I doubt they are saying that the star existed from soon after the Big Bang until 6,000 years ago, so how can this be explained?Honeyman2010 (talk) 05:52, 13 February 2014 (UTC)

Your doubts are mistaken. They are in fact saying it has existed for 13.6 billion years. Small stars take a long time to burn out. The sun will run ~9 billion years (it's been 4.5 so far), but even smaller stars should be able to burn for 10s or even 100s of billions of years. They believe SMSS J031300.36-670839.3 is very old because it has almost no heavy elements, and hence belongs to Population II. Hence the claim is that it is a small star that formed shortly after the Big Bang and has burned continuously since then. Dragons flight (talk) 06:11, 13 February 2014 (UTC)

Thanks for your answer. The article I read was brief and did not explain that this was perhaps a red dwarf or something similar, which I know can theoretically live for trillions of years or longer. Honeyman2010 (talk) 07:02, 13 February 2014 (UTC)

Perhaps you are making the common mistake of failing to make the distinction that a light year  is a unit of length/distance, and has no direct relation to time — except as related to the speed of light. It's analogous to calling a mile a "train minute" —if  you assume that all trains traveled at exactly 60 m/h.  ~:71.20.250.51 (talk) 06:24, 13 February 2014 (UTC)

• There is an ambiguity in the word "oldest". It can mean either "longest lived" (as it does here) or "originating the longest time ago" (as the OP understood it). Looie496 (talk) 15:57, 13 February 2014 (UTC)

I see a person in front of me. He claims to be 17 years old, but he's only 3 light-nanoseconds away! If I am seeing light that is only 3 nanoseconds old, how can it have come from this person, who is supposedly 17 years old? --Bowlhover (talk) 16:08, 13 February 2014 (UTC)

• Note that for the oldest star to be in our own galaxy is quite a coincidence when you think about it... but there's a reason. Even in something as close as the Andromeda Galaxy, we're seeing about 2.4 million years of history, 0.02% of the lifespan of the universe omitted because that's when the light was sent. I'm not exactly sure how they dated the star - the article I just read said the star had to have formed a "couple of hundred million" years after the Big Bang, as determined by a "complete absence" of iron. But probably whatever cosmological window they're looking at is a relatively narrow period of times of formation, so stars in any but the nearest galaxies couldn't possibly be as old at least as their light appears to us. Though more likely it's just selection bias from them only looking for these in nearby stars. Wnt (talk) 22:49, 15 February 2014 (UTC)

They measure the age by the ratio of helium to hydrogen indicated by the star's spectra. Given the lack of metals they can assume it is a population two star, and those stars began burning with a certain percentage of helium compared to oxygen. That changes over time with a predictable rate given the star's temperature. See stellar spectroscopy. μηδείς (talk) 02:45, 16 February 2014 (UTC)

6,000 light years isn't merely in our galaxy but also relatively close within the galaxy. I guess it's simply easier to get good measurements this close. I'm not an astronomer and was surprised to see there is nothing older known in List of the most distant astronomical objects. PrimeHunter (talk) 03:06, 16 February 2014 (UTC)

A star like this will be a dim red dwarf. The only stars that can be individually made out in other galaxies are novae or extremely bright and very short-lived stars like Wolf-Rayets:

A red dwarf is a small and relatively cool star on the main sequence, either late K or M spectral type. Red dwarfs range in mass from a low of 0.075 solar masses (the upper limit for a brown dwarf) to about 50% of the Sun and have a surface temperature of less than 4,000 K.

Red dwarfs are by far the most common type of star in the Milky Way galaxy, at least in the neighborhood of the Sun, but due to their low luminosity, individual red dwarfs cannot easily be observed. From Earth, not one is visible to the naked eye. Proxima Centauri, the nearest star to the Sun, is a red dwarf (Type M5, apparent magnitude 11.05), as are twenty of the next thirty nearest.

According to some estimates, red dwarfs make up three-quarters of the stars in our galaxy.

Stellar models indicate that red dwarfs with less than 35% of the Sun's mass are fully convective. Hence the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout the star, avoiding a buildup at the core. Red dwarfs therefore develop very slowly, having a constant luminosity and spectral type for, in theory, some trillions of years, until their fuel is depleted. Because of the comparatively short age of the universe, no red dwarfs of advanced evolutionary stages exist.It won't be visible from another galaxy.

μηδείς (talk) 03:57, 16 February 2014 (UTC)

Brass cylinder

on a cyllinder of iron brass metal is perforated of 1mm thicness in niddle shape and above it foam is coated and on the upper most part of cyllinder onther insulation is made .if it is placed in a room where petrolium catches fire then will brass melt or not08:15, 13 February 2014 (UTC)~ — Preceding unsigned comment added by 203.197.118.97 (talk)

It depends how hot it gets. The melting point of brass is 900 to 940 °C, 1652 to 1724 °F. The autoignition temperature of petroleum is only 280 °C (536 °F). Are there other combustible materials in the room?--Shantavira|^{feed me} 08:46, 13 February 2014 (UTC)

There isn't enough information to answer. The autoignition point gives us a ballpark minimum temperature, but no upper bound! The flame might be much hotter, if conditions are right. The flame temperature is necessary, but not sufficient: we'd also need to know the "power budget," so to speak, for the rate of energy input by the fire, and the rate of heat-loss through the walls, doors, and windows... we'd need to know if the flame persists forever (is it fed with fresh air and fuel?), and so on. We'd need the exact type of brass and petroleum, too. There are a lot of unknowns. Nimur (talk) 08:51, 13 February 2014 (UTC)

You also say "iron brass metal" - is it iron or is it brass? Makes a huge difference. Also, "brass" is a very vague term - it's an alloy of copper and zinc - but the exact proportions can vary tremendously and brass mixes often add other metals, which will vary the melting point tremendously. SteveBaker (talk) 20:23, 13 February 2014 (UTC)

Is this real: Exchange spring magnet

Is this real: Exchange spring magnet? Searching for the phrase finds hits, but the page. Ouch. I can't tell if it's just poor English, or a joke. The person who wrote that page even created and added illustrations! Ariel. (talk) 19:49, 13 February 2014 (UTC)

I fixed the link to their first reference. It seems plausible that it is related, and there are just major English problems. The term "exchange spring" doesn't show up, but the article does talk about balancing "exchange forces" in engineered magnets. You should probably also bring this up on the talk page of the article, but hopefully others here can figure out if there are any useful references that can be used to figure out what the article is trying to express. Katie R (talk) 20:12, 13 February 2014 (UTC)

The user appears to be Chinese, which would account for the questionable English. As for validity of content, I have no clue. Justin15w (talk) 20:14, 13 February 2014 (UTC)

I think it's trying to be a useful article - but it needs a heck of a lot of work. Problem being that it's a fairly narrow field, so there may not be many experts around here to review it. Usually, that's OK because you can just compare what each paragraph says against the linked reference sources - but although this article has references, they aren't linked to the text. A very problematic situation. I think it would be a good idea to discuss it in WikiProject Physics or something. SteveBaker (talk) 20:20, 13 February 2014 (UTC)

Yes, it sounds genuine to me, but it would be useful to have an opinion from an expert in the "magnetic field" before we start work on improving the sentence structure. Dbfirs 21:50, 13 February 2014 (UTC)

Looking again, the actual exchange spring section of the article is much clearer. Reading through it I think I understand at a basic level how the mix of magnetic materials work together to give the properties described, although it could certainly use a lot of improvement. The vast difference in style in an article submitted by one user makes me worry there may be a copy vio, but a quick search of some of the text doesn't bring up anything other than our article. Katie R (talk) 13:09, 14 February 2014 (UTC)

Two people who have done a lot of work on the Magnetic field article are User:TStein and User:RockMagnetist. I'll see if they will have a look at it. Richerman (talk) 22:25, 14 February 2014 (UTC)

There is such a thing as an exchange spring magnet. I'll have a look. RockMagnetist (talk) 23:05, 14 February 2014 (UTC)

Excellent! Thank you. Richerman (talk) 11:24, 15 February 2014 (UTC)

Studying science

When studying a year long science related course, is it better to do practice questions throughout as you study topics or is it sufficient to understand all topics then do practice questions at the end of the year? 82.40.46.182 (talk) 23:51, 13 February 2014 (UTC)

How will you know whether you understand topics without doing practice questions? Test your knowledge as you go along, and you'll be more confident of not missing anything at the end of the year. AndyTheGrump (talk) 23:56, 13 February 2014 (UTC)

What about going through worked examples by hand? 82.40.46.182 (talk) 00:11, 14 February 2014 (UTC)

Everyone and every course is different, what works for you might not work for someone else. The curriculum is usually designed to give as many people as possible the best chance at succeeding. If you have specific questions about the material, you should really discuss them with your course provider or lecturer. No one here will be able to tell you what will work for you. Vespine (talk) 00:28, 14 February 2014 (UTC)

Assuming the eventual exam involves you actually doing problems rather than just following someone else doing them and saying "yes, that seems reasonable", "going through worked problems" doesn't sound like it is equivalent to know you actually understand the topics sufficiently. The more you defer until the end, the more you may wind up with a massive amount of learning to do if you find you actually don't understand various topics well enough to do actual practice problems. Are science courses really that compartmentalized that you can get through the whole year and have it not matter until the end whether you can actually do certain kinds of problems? DMacks (talk) 04:33, 14 February 2014 (UTC)

Personally, when it comes to science, or mathematics, I don't think you can really learn the material without doing problems; I've always seen the reading part as less learning and more giving you enough to start learning by doing - for an analogy: you can read novels all day, but if you want to write a decent one yourself, you need to spend a ton of time writing as well (reading alone just won't do it); the same applies to science and math stuff. If your main activity is just reading, you may convince yourself you understand it, but you won't.Phoenixia1177 (talk) 07:26, 14 February 2014 (UTC)

Do you think this is more so for maths and physics related sciences and less so for chemistry and biology as they tend to be less qualitative? 82.40.46.182 (talk) 08:05, 14 February 2014 (UTC)

To be honest, I don't study much chem/bio; but, I think this, actually, is pretty universal. In general, reading about a subject will not enable you to do it, not even at an average level - with almost anything worth doing, you really need to do it. In fact, I would go so far as to say that reading is for when you don't know enough to try it (or after you tried); when I seriously want to learn something, I put the book down every few sentences, then try and figure out where it will end up by working out the ideas on my own, then resume reading. This works exceptionally well: learning is an extremely involved and active thing, passively reading and memorizing is not going to suffice for anything but a cursory understanding.Phoenixia1177 (talk) 08:13, 14 February 2014 (UTC)

I don't know what you mean by " chemistry and biology as they tend to be less qualitative." Exercises in both, at least, it seems to me, could be calculating an amount, analyzing a problem, establishing relationships and the like.

Anyway. Drills are not there to check whether you understood something. They are a learning experience per se. You'll remember long what you do, than what you simply saw. If the exercises are boring they are either too easy or too hard and you just need other exercises, but do not skip them. OsmanRF34 (talk) 12:49, 14 February 2014 (UTC)