Science desk
< October 25	<< Sep \| October \| Nov >>	October 27 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 26[edit]

Digestion[edit]

Are any gases released during digestion? (like oxygen) —Preceding unsigned comment added by 24.86.167.133 (talk) 01:46, 26 October 2010 (UTC)[reply]

Oxygen is not released. It's methane and CO2 mainly. Technically they are released by gut flora, and not by the human. Ariel. (talk) 05:34, 26 October 2010 (UTC)[reply]

See Flatulence. Cuddlyable3 (talk) 08:45, 26 October 2010 (UTC)[reply]

Angular momentum[edit]

My textbook derives the relationship [J_x, J_y] = ihJ_z (I can't make h bars) by defining the J's as the generator of their respective Rotation operators...but only for the Rotation operators in regular Euclidean space (ie $R(\theta k)={\begin{bmatrix}\cos \theta &-\sin \theta &0\\\sin \theta &\cos \theta &0\\0&0&1\end{bmatrix}}$ ). How do we know/show that this holds for the more general rotation operator over a ket space? 76.68.247.201 (talk) 04:37, 26 October 2010 (UTC)[reply]

Chapter 2, page 7 and further Count Iblis (talk) 14:54, 26 October 2010 (UTC)[reply]

I'll try and understand the link, but thanks a lot! 76.68.247.201 (talk) 20:40, 27 October 2010 (UTC)[reply]

Evaluating IQ without math[edit]

I've tried to pass IQ test, but seems like it always involves some tough math calculations, which I don't like (so I still don't know my IQ). Nonetheless I'm quite familiar with geometry. Is there some other way to measure the IQ? 85.222.86.190 (talk) 08:36, 26 October 2010 (UTC)[reply]

Wikipedia has an article Intelligence quotient about IQ testing. The picture at the top of the article shows an example test item which you will see is a geometrical test. Properly designed IQ tests are not based on math. Cuddlyable3 (talk) 08:43, 26 October 2010 (UTC)[reply]

I've taken multiple IQ tests and none of them have contained "math". They do contain numbers, sequences, pattern matching, spacial analysis, etc... All of that could be mistaken as math, but it isn't. It is the primary point of an IQ test. It isn't a test of how intelligent you are. It is a test of how well you learn new patterns and processes and apply those to problems. -- kainaw ™ 13:06, 26 October 2010 (UTC)[reply]

I agree, I've taken a couple IQ tests through the public school system, and besides perhaps a little basic arithmetic of small numbers, there was no math. There were some problems that had numbers, but no advanced computation was required, just pattern recognition, problem solving, and such. APL (talk) 16:05, 26 October 2010 (UTC)[reply]

Any IQ test you take that is "tailored" to your likes and dislikes is as useful as a screen door on a submarine. Take the real IQ test and whatever you get as a score is your IQ. Go learn some math! —Preceding unsigned comment added by 165.212.189.187 (talk) 13:50, 26 October 2010 (UTC)[reply]

Apologies for the unhelpful, incorrect and snarky reply from 165. There is no `real' IQ test, and picking one that is `tailored' to minimize bias is probably helpful in getting reliable results. The usefulness / meaning of the IQ concept is also contentious, see IQ#Criticism_and_views for starters. The OP may like this IQ test [1], which uses no words or numbers, just visual geometric patterns. This makes it a good tool for assessing how good one is at pattern recognition; extrapolate additional meaning at your own risk. --SemanticMantis (talk) 14:53, 26 October 2010 (UTC)[reply]

Quantitative analysis and pattern recognition are related to mathematical thinking. Many IQ tests use algebra or other "learned" skills in order to rapidly assess quantitative skills. There are many different IQ tests, and many different definitions of IQ, but it is safe to say that most psychologists consider mathematical capability to be an intrinsic part of intelligence quotient. You should read our article to understand what IQ actually is and how it is used, as well as the preferred ways to measure it. On the one hand, test designers want to avoid cultural biases and test inherent ability as opposed to learned skills; on the other hand, they also want to tests mathematical aptitude, because they consider mathematical ability an important element of intelligence. Imagine the SAT without a math section! (Of course, the SAT is an "aptitude" test and not an "intelligence quotient" test, but that is a euphemism and a trademarking/marketing ploy. SAT is highly correlated to IQ; for practical purposes, they both indicate the same thing. Nimur (talk) 15:34, 26 October 2010 (UTC)[reply]

I think a lot of the criticism of IQ would go away if it were called something like "Logical Thinking Quotient" instead of a name that grandly implies that the test measures "intelligence" as a whole. APL (talk) 16:05, 26 October 2010 (UTC)[reply]

I agree; that's why prominent agencies use a "euphemism" for it - such as "scholastic aptitude." This is a good thing - it's not just "political correctness," it's an effort to use a more proper terminology. As our article notes, the validity and significance of IQ is highly debated. In fact, every scholarly analysis I have every seen about standardized intelligence metrics prefaces all discussion with a disclaimer to the effect that intelligence metrics only measure whatever it is that they measure. Nimur (talk) 18:26, 26 October 2010 (UTC)[reply]

Just to clarify, the SAT is no longer intended to be an aptitude test, and no longer correlates with IQ as well as it used to. For a while, SAT stood for "Scholastic Assessment Test", and now is not an acronym for anything (officially). The SAT was originally designed to pretty much be an IQ test, but as "IQ testing" got sort of a bad rap in the mid to late twentieth century, it was redesigned to not be an intelligence test. Mensa, for example, will not accept SAT scores from after the 1994 redesign as evidence of intelligence [2]. Buddy431 (talk) 19:17, 26 October 2010 (UTC)[reply]

Any "IQ" test that requires the prior learning of anything is culturally biased. (That means they all are.) HiLo48 (talk) 20:03, 26 October 2010 (UTC)[reply]

Ironing interferes with digital TV reception[edit]

My UK freeview digital reception through a TV aerial is very weak (as measured by the signal indicator on the digibox) but usually sufficient for trouble-free viewing. However, I've noticed that when I iron clothes the signal deteriorates significantly (tends to break up). There's some tendency to get even worse when I tilt the iron downwards and it generates steam. They're plugged into the same power outlet. I don't observe other devices suffering a similar problem when ironing (no crackles from the hi-fi speakers, etc.) so I'm not convinced there's an electrical fault on the iron). Is it possible that the power used by the iron means that the digibox is somehow less able to process the signal it receives? Is the iron generating a field that interferes with the box? --Frumpo (talk) 10:18, 26 October 2010 (UTC)[reply]

Are we referring to an internal aerial here? If so have you considered the possibility the steam for example is interfering with the reception? Nil Einne (talk) 10:40, 26 October 2010 (UTC)[reply]

No, the aerial is up on the roof. --Frumpo (talk) 11:00, 26 October 2010 (UTC)[reply]

When the USA was having its debate over digital TV standards, the U.S. manufacturers claimed the European standards were particularly susceptible to "impulse noise" -- essentially a sudden electrical spark or electrical arcing, which creates a short momentary radio wave pulse. Even though it would be too short (and maybe too low power) to hear on analogue hi-fi speakers, the little radio wave click would be enough to upset all of the digital signal bits being transmitted at that moment, which could create a major glitch in the picture. The European standard was said to be much better at dealing with "multipath" interference -- ie the effects of reflections causing multiple versions of the same signal to be received, that would show up as "ghosting" on an analogue TV; but a bit worse at dealing with impulse noise. Impulse noise particularly gets caused by electric motors, where you get little electric arcs at the brushes that keep electrical contact between the stationary and the moving parts -- so vacuum cleaners, kitchen equipment, washing machines were particularly identified as troublesome. But it seems conceivable that if you had a low-level dodgy connection inside the iron (or if the iron's thermostat keeps switching on and off) that this might produce something similar. Jheald (talk) 11:01, 26 October 2010 (UTC)[reply]

If you were to plug the iron into another power socket, would the reception be similarly affected? If not, you have your answer! --TammyMoet (talk) 11:08, 26 October 2010 (UTC)[reply]

A iron should not generate any interference except when the termostat turns on or off. If it does it is probably faulty, probably bad contact somewhere. --Gr8xoz (talk) 14:25, 26 October 2010 (UTC)[reply]

You also get noise when you put the iron down on the metal resting place. When I was a teenager I sometimes listened to shortwave radio and whenever my mother was ironing, I would hear the interference. This precisely when she was putting the iron down to move or change the clothes she was ironing. Count Iblis (talk) 14:44, 26 October 2010 (UTC)[reply]

Thanks everyone. I'll try using a different socket but I suspect that Jheald has identified the problem. The iron is designed so that steam is only generated whilst it's in the horizontal position. So, when I'm ironing, I guess there is a switch that's constantly flipping as I move the iron between the horizontal and vertical positions (in addition to the thermostat maintaining the temperature). What Count Iblis says is also observable but maybe that's because the iron is returning to the vertical position at the same time as it's being put on the metal resting plate. Or, is there some additional interference that could be caused by placing the iron near the metal plate? --Frumpo (talk) 15:29, 26 October 2010 (UTC)[reply]

Another test you could do is to borrow someone else's iron for a while, and see if a different iron gives the same interference. Physchim62 (talk) 17:11, 26 October 2010 (UTC)[reply]

Number of people on earth[edit]

How many people have been on earth (all time)? 173.49.140.141 (talk) 12:50, 26 October 2010 (UTC)[reply]

See this from 2002. Back then, a good estimate was 106,456,367,669. -- kainaw ™ 13:03, 26 October 2010 (UTC)[reply]

Articles on everything: Total number of humans to have ever lived. --Ouro (blah blah) 13:11, 26 October 2010 (UTC)[reply]

Highest rank with only one species in it?[edit]

What rank is the highest that (in any domain) has only one known species? I found an order: Tubulidentata (aardvark), but there might be a higher rank: Family, Class, ... with only one species. --Eu-151 (talk) 13:54, 26 October 2010 (UTC)[reply]

It seems to depend on the taxonomist, but Limnognathia has been classified as the only member of its phylum. -- Finlay McWalter ☻ Talk 14:10, 26 October 2010 (UTC)[reply]

The same is true of the ginkgo biloba. Nyttend (talk) 00:19, 27 October 2010 (UTC)[reply]

That used to have a lot more species in it though... Smartse (talk) 11:20, 27 October 2010 (UTC)[reply]

Magnetic flux and electricity[edit]

Hi, can anyone please assist:

I would like to know whether one could generate an electric current in a conductor that is moving between two magnets REPELLING each other on either side of the conductor? In other words, must the magnets be attracting each other or can they repel also?

Thanks —Preceding unsigned comment added by 209.203.29.62 (talk) 15:14, 26 October 2010 (UTC)[reply]

It requires a magnetic field. When the magnets are repelling each other, their magnetic fields cancel out. It won't necessarily be perfect. If one magnet is bigger or closer, there will still be a current, but you'd be better off just having one magnet. — DanielLC 16:48, 26 October 2010 (UTC)[reply]

Yes, a permanent magnet generator can be constructed with magnets mounted in a repelling orientation. If the conductor moves directly between the two repelling magnets, not much will happen, as Daniel mentions above. However, repelling magnets still create a field that coils can take advantage of if shaped and located properly. Here's an example; [3] __TunqstenCarbide XXXII (talk) 23:35, 26 October 2010 (UTC)[reply]

It would be wasteful to use magnets in a repelling orientation in a generator. At the null point, there would be absolutely no electricity generated. Move the windings closer to one or the other poles, and some electricity would be generated, but less than if the other magnets had not been installed. Thus it would seem to be an idiotic and wasteful design. Edison (talk) 05:13, 27 October 2010 (UTC)[reply]

that's perhaps a strong statement. Are you sure you understood how the design I mentioned works - seems not? Look at the FEA, mid page. Most coreless PMAs have iron backing rings to complete the magnetic circuit - the example I give is an ironless design, so perhaps it's useful if one had a reason to eliminate weight. Also, Halbach arrays have a fair amount of repulsion in their design (if you've ever tried to assemble one you'd know this), and they definitely have uses, including the elimination of iron or other magnetic material to complete the magnetic circuit. __TunqstenCarbide XXXII (talk) 07:02, 27 October 2010 (UTC)[reply]

Tachyon[edit]

Can someone explain tachyons in simple words? 173.49.140.141 (talk) 15:21, 26 October 2010 (UTC)[reply]

In advanced physics, we use theories about particles to explain certain measurements. A particle is a small "object" that has some property - usually, it has a position and a velocity, and most of the time also has a mass and a momentum and a few other numbers associated with it. In high-energy physics, we sometimes expect an extra particle to exist, even when we don't see it, in order to explain why our measurements are as they are. So, we sometimes "guess" that there is a particle that we haven't seen, but that is responsible for some measurement. Tachyons were one such "guess" - but we have never actually seen any reason that they should exist, or do exist. Experiments have almost ruled out the existence of tachyons, by requiring them to have physical properties that do not make sense (like having an imaginary number value for the mass). Nimur (talk) 15:40, 26 October 2010 (UTC)[reply]

For questions like this it's sometimes worth checking the "simple english Wikipedia" article on the subject. APL (talk) 15:57, 26 October 2010 (UTC)[reply]

As far as anyone knows tachyons do not exist. So why do we talk about them? They basically are a result of the math used to calculate speed. If you plug in a speed above the speed of light you get a weird result, and we call the result "tachyons". In physics if you don't have the math for it, it doesn't exist. Conversely if there is math for it there is a claim that it may exist. That doesn't mean it always does, but very very frequently it does. There are many particles that were found because someone noticed something in the math, and looked there. Ariel. (talk) 18:37, 26 October 2010 (UTC)[reply]

Tachyons are about one step up from unobtainium, in the sense that we can invent mathematical derivations of existing models which perhaps, maybe, could allow for the existance of tachyons. But they probably don't exist. --Jayron32 05:41, 27 October 2010 (UTC)[reply]

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' (I've found it!), but 'That's funny...'" - Isaac Asimov, or perhaps not. CS Miller (talk) 12:15, 27 October 2010 (UTC) [reply]

relation between friction and area[edit]

in physics we read frictional force does not depend upon area of contact provided normal remains same. In chemistry under topic of viscosity we read frictional fore is directly proportional to area.

Also according to classic physics

" friction exists becoz of locking of two layers"

if it is so area should be directly proportional to the frictional force as more the area, more will be the locking means more force needed to overcome it ie more friction.

according to Modern physics

"friction is the force needed to break the bonds(cold welding)between the two surfaces "

[i.e. why if we make something extra smooth friction will increase tremendously]

if it is so then also area should be directly proportional to the frictional force as more area means more bonds means more friction.

thanX .... i think i explained it pretty well.--Myownid420 (talk) 16:26, 26 October 2010 (UTC)[reply]

This has been discussed many times here. (here's one such discussion.). Basically, the approximation you learn in highschool for calculating friction really only works well in certain situations with perfectly ridgid objects. (Like the steel spheres you might use for experimenting!) In real world calculating friction is surprisingly complex, and not a 100% solved problem. APL (talk) 16:38, 26 October 2010 (UTC)[reply]

Yes, friction is complex in reality, but there is a much simpler explanation for the apparent discrepancy. Friction is indeed proportional to area, but also to normal force. In a fluid, the normal force (per unit area) tends to be independent of area, whereas in the simplified school physics example, the normal force (per unit area) is inversely proportional to the area of contact, hence the total friction force for a solid block is approximately independent of the contact area. Dbfirs 17:23, 26 October 2010 (UTC)[reply]

When there is less area, there is a stronger force per unit area pushing the two surfaces harder together. This makes the friction approximately the same. --Chemicalinterest (talk) 00:56, 27 October 2010 (UTC)[reply]

But not always because this would not run well on these. Cuddlyable3 (talk) 17:20, 27 October 2010 (UTC)[reply]

Good point! How much of the difference is caused by deformation? It would be interesting to find out if the difference is present in a static test. Dbfirs 00:29, 28 October 2010 (UTC)[reply]

Lagrangian point[edit]

My memory of the physics I took in the 1970s is that determining the location of Lagrangian points involved the solution of a fifth-degree equation. Is that right or is my memory wrong? Bubba73 ^{You talkin' to me?} 17:06, 26 October 2010 (UTC)[reply]

There are a lot of ways to derive the Lagrange points. Conventional derivations use Lagrangian mechanics (surprise!) Our article links to a few derivations; Here is a derivation by Prof. Cornish at Montana State University, and more mathematical elaboration. "The brute-force approach for finding the equilibrium points would be to set the magnitude of each force-component to zero, and solve the resulting set of coupled, fourteenth-order equations for x and y," but using symmetry, Prof. Cornish simplifies this significantly. Such simplification could be written algebraically as a 5th-order equation (surely, the five points come from the five roots where some equation defining the magnitude of the net force equal zero). But writing that out, and then solving it, might be horrible. As I recall, this is similar to the approach in Marion & Thornton's textbook on classical dynamics - though they don't provide a full solution. Nimur (talk) 18:52, 26 October 2010 (UTC)[reply]

Yes, I was thinking that the five points came from the roots of a fifth-degree equation. Thanks. Bubba73 ^{You talkin' to me?} 18:57, 26 October 2010 (UTC)[reply]

Orangutan strength[edit]

How strong are adult male orangutans? I know that chimps have about five times a human's strength and gorillas have about 20 times as much strength, but does anyone have such a figure for orangutans? And how aggressive are they? Have there been any documented cases of attacks on humans (not counting sexual assaults)? --The High Fin Sperm Whale 23:29, 26 October 2010 (UTC)[reply]

Estimates seem to range from over 4x[4] to 7x[5]. Clarityfiend (talk) 00:46, 27 October 2010 (UTC)[reply]

Of course it's fictional but I can't resist mentioning The Murders in the Rue Morgue in this context. Looie496 (talk) 17:46, 28 October 2010 (UTC)[reply]

Double Displacement Reactions[edit]

Hello. If the conditions for a double displacement reaction to proceed are one of:

precipitation,
evolution of gas, or
acid-base neutralization;

can CuO react with H₂SO₄ to yield CuSO₄ and water? Since the products are soluble and not gaseous, is CuO a basic oxide? What determines an oxide salt to be a basic oxide? Thanks in advance. --Mayfare (talk) 23:51, 26 October 2010 (UTC)[reply]

Maybe "unprecipitation" counts, too. The net ionic equation is CuO + 2 H⁺ → Cu²⁺ + H₂O In this case the H and the Cu switch places. --Chemicalinterest (talk) 00:53, 27 October 2010 (UTC)[reply]

Copper(II) sulfate is quite soluble in water, so you wouldn't so much form CuSO₄, but rather Copper(II) ions and sulfate ions in solution. But yes, copper oxide is a basic oxide, and will thus dissolve in mineral acids like sulfuric acid (though "double replacement" is really a simplistic way of looking at it). As for basic versus acidic oxides, more electronegative elements form acidic oxides, while less electronegative elements form basic oxides (in general). Some oxides of elements that are sort of in the middle can go both ways: ZnO and Alumina, for example. Higher oxidation state metal oxides can also form acidic oxides, like Chromium trioxide. Buddy431 (talk) 01:47, 27 October 2010 (UTC)[reply]

"Double replacement reactions" is the sort of stuff we teach to first semester high school students to simplify models of chemical reactions into basic model reactions (synthesis, decomposition, single replacement and double replacement). It's not really used as a concept in "real" chemistry; rather it is a gross simplification used as a means build upon later in teaching more accurate models. This is a common pedagogical tool; you teach a very inaccurate, but very easy to understand model, and then you build more accurate models upon it, abandoning the old models. It's like teaching a kid to ride with training wheels, knowing eventually he will be riding a regular bicycle. See Lie-to-children. During the first few weeks of class, you start with the "double replacement" model, eventually you abandon it when you start to work with net ionic equations. --Jayron32 05:36, 27 October 2010 (UTC)[reply]

Realise the reason why copper sulfate is soluble in water whereas copper(II) oxide isn't is because sulfate isn't terribly good at sticking to copper(II), but the very basic oxide ion (it's an oxygen ion with two negative charges!) has a super affinity for Cu(II). That oxygen's negative charge is very concentrated, whereas in sulfate it is delocalised through resonance (chemistry). So acid attacks the basic oxide ion, turning into non-basic water. Then it can no longer bind copper(II) as well, bringing it into solution with the counterion of whatever balanced the H+. Realise the reason why HCl and H2SO4 are strong acids are because Cl- and sulfate usually are spectator ions, cannot bind H+ well and do nothing, leaving free H+ to do its work. On the other hand, water is not a strong acid because its conjugate base is the hydroxide ion, which binds H+ very well....John Riemann Soong (talk) 03:27, 28 October 2010 (UTC)[reply]

The difference between the sulfate ion and the oxide ion is due mostly to electrostatics. They both have a 2- charge, but the oxide ion is tiny, making a very concentrated 2- charge, in a lattice of copper (II) ions and oxide ions, the small oxide ion is very close to the copper (II) ion, making the force of attraction between them very large, making them hard to "pull apart". The sulfate ion is huge, by comparison, meaning that it is "soft" in the sense that the charge is spread out over a larger area (see HSAB for discussion of this definition of softness). Also, because of its larger size, it is much farther from the copper (II) ion in the solid lattice, meaning that the force of attraction is less (compared to the oxide). All other things being equal, it requires much less energy to separate the sulfate from the copper than to seperate the oxide from the copper, mostly due to the size differences. --Jayron32 04:07, 28 October 2010 (UTC)[reply]