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June 11

Balloon on bus accelerating forward.

This was a problem from a physics book I vaguely remember; I never quite figured it out and someone else's question reminded me. A bus is accelerating forward. A balloon is tied to a string attached to a chair. Why does the balloon go forward as well. If I remember correctly it was from one of the Feynman lectures on physics book so I doubt the question is wrong. But to me it would seem the balloon should go backwards, not forwards. Any possible explanations that involve simple Newtonian mechanics (nothing about fluids or pressure; I don't think it said WHAT the balloon was filled with but I'm assuming standard balloon with helium.24.171.145.63 (talk) 03:16, 11 June 2009 (UTC)[reply]

:By who's perspective? To a person on the bus, the balloon will drift backwards, until the string stops it, and then it will go forwards with the bus. However, to a person standing on the street, the balloon will drift forwards but at a rate slower than the bus does, since the air in the bus generates a small amount of friction on the balloon, and will push if forward slightly. --Jayron32.talk.contribs 03:28, 11 June 2009 (UTC)[reply]

No Jayron, the balloon actually moves foward (even from the perspective of the person inside the bus) because the air around the balloon is heavier than the balloon and moves backward forcing the balloon forward (just as it falls downward, forcing the balloon upward). Dauto (talk) 03:48, 11 June 2009 (UTC)[reply]

Ah yes, of course. That makes sense. Scratch my earlier reply. --Jayron32.talk.contribs 03:56, 11 June 2009 (UTC)[reply]

Actually ... when the bus accelerates several forces will affect the ballon's motion:

the motion of the bus, pulling the string -- the most significant force, causing the balloon to move forwards with the bus
the balloon's inertial mass -- causing it to drift backwards relative to the passengers
assuming calm atmospheric conditions (no wind), air pressure or friction would be a small factor opposing the balloon's drifting motion —Preceding unsigned comment added by Ropata (talk • contribs) 09:35, 11 June 2009 (UTC)[reply]

You forgot its bouyancy, which is the one which causes it to drift forwards relative to the bus. Elocute (talk) 10:14, 11 June 2009 (UTC)[reply]

Also, the bus will pull the string in the opposite direction the balloon is being pushed. If it is indeed moving forward, the bus will pull the balloon back. — DanielLC 14:10, 11 June 2009 (UTC)[reply]

Yes bouyancy is the key here. The gas in the balloon is lighter than air (which is why it's floating). Imagine a cork floating in a glass of water in the bus. As the bus accelerates forwards - the water in the glass sloshes towards the back of the bus - which forces the lighter cork to move forwards. That's very easy to visualize because you can see the water. However, the same thing is happening with the balloon which is floating in the air. When the bus accelerates, the air sloshes towards the back of the bus - forcing the balloon to move forwards...it seems counter-intuitive - but that's because we're not used to seeing things that are lighter than air. SteveBaker (talk) 12:06, 11 June 2009 (UTC)[reply]

We need to state that we are referring to a balloon that has positive buoyancy--it would rise toward the ceiling if untied. My daughter's physics class was given this problem, and the debate was so fierce that she drove to a store, purchased a balloon, and verified by experiment that the balloon goes forward. I pointed out to her that one result of general relativity is that accelerated frames of reference are indistinguishable, if the buoyant force opposes gravity, it must also oppose any other acceleration. on the bus, if you tie a plumb bob and a balloon to the same pivot point, the two strings will form a straight line in steady state tilt or steady state acceleration. -Arch dude (talk) 13:03, 11 June 2009 (UTC)[reply]

Yes, the equivalence principle is the easy way to see this. A bus accelerating forward is equivalent to a bus tilted backward (in both cases you're pressed into your seat). A helium balloon has to behave the same relative to the frame of the bus in both cases, and that means moving diagonally in the front-ceiling direction. -- BenRG (talk) 16:17, 11 June 2009 (UTC)[reply]

Why would the balloon move forward? I don't understand the part about the air inside the bus "sloshing" backwards. Yes, there will be "sloshing," but will it be only backwards? I think such "sloshing" will be complex, going around the seats and any other complexity to what otherwise might be a simple geometric volume. Supposing instead of a bus, we were considering a hollow cylinder. And instead of windows, which might be opened or closed, we considered the cylinder totally closed. Would the balloon still move forward? If so, that would be assuming that the air at the back of the cylinder became more dense, or compressed, than the air at the front of the cylinder. But is this really the case, to any appreciable degree, at acceleration rates concerning busses? I have my doubts about that. In theory that sort of reasoning might apply. But I am not so sure it applies in a bus accelerating from a standstill, no matter how fast the driver attempted to accelerate the bus. I think a more likely explanation for the balloon moving forward might be complex air currents resulting especially from open windows. But I am not sure. Bus stop (talk) 16:37, 11 June 2009 (UTC)[reply]

Yes, even in your cylinder example, it would happen. Yes, the acceleration causes an increase in density at the rear of the bus. If the bus starts turning left, the density will increase on the right and the balloon wil move to the left.--Sphilbrick (talk) 16:42, 11 June 2009 (UTC)[reply]

Yes, that's exactly what happens. The air at the back of the balloon becomes more dense than the air at the front of it creating a pressure gradient force on the balloon that's enought to push it forwards. This is entirely equivalent to the vertical pressure gradient that makes the balloon float. Dauto (talk) 18:24, 11 June 2009 (UTC)[reply]

Do you understand why the balloon floats in the first place? The reason it moves forward under acceleration is exactly the same as the reason it floats. In a completely sealed cylinder in steady-state 1G forward acceleration, the balloon will be at an angle of 45 degrees even though there is no air movement whatsoever. You really need to purchase a balloon and get someone else to drive you and accelerate. The effect is dramatic, not subtle at all. -Arch dude (talk) 19:55, 11 June 2009 (UTC)[reply]

Interesting. Thank you. Bus stop (talk) 18:28, 11 June 2009 (UTC)[reply]

Another way to approach this problem is using the Equivalence principle:("we [...] assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system." - Einstein, 1907). If the vehicle is accelerating at say 9.8m/s/s it may equivalently be modeled as a gravitational field of 1g, within this vehicle, oriented opposite to the direction of the acceleration vector. This creates a pressure gradient ( just like gravity creates a pressure gradient in fluids) which causes the balloon to move forward - just as a hydrogen balloon would rise up as a result of the pressure gradient created by gravity. Dilip rajeev (talk) 20:02, 16 June 2009 (UTC)[reply]

Aight thanks guys 24.171.145.63 (talk) 19:25, 11 June 2009 (UTC)[reply]

Y Chromosome

If I understand genetics correctly (hopefully I do) then everything that makes a person male comes from their father via the Y chromosome, whereas what makes a person female comes from one X chromosome of the mother and father respectively.

Therefore does this fact of nature indicate that generally men (or male animals even, if this helps rule out the cultural and psychology influences) would prefer the birth of a son?

In other words, a father completely influences the male characteristics of his sons but only half the female characteristics of his daughters. So in the interest of passing on one's genes (which according to The Selfish Gene and natural selection indicates is the main reason for competition for mates and for having children) wouldn't men prefer sons while women would be indifferent? Perhaps this also explains why inheritance laws have typically favored sons in most cultures? TheFutureAwaits (talk) 09:54, 11 June 2009 (UTC)[reply]

It seems to me that since males have no female parts, they wouldn't influence a female offspring at all. Rather, the fathers female ancestors gens, plus the mothers genes, would control the female parts.

As for whether this affects favoritism or not, is beyond me.Drew Smith What I've done 10:31, 11 June 2009 (UTC)[reply]

My apologies if I'm stating the obvious, but men are XY and women are XX. Therefore men do influence half of what makes their daughters female (in terms of sex chromosomes; female being the "default" sex is an issue beyond the scope of this question). You know:

Xm1Ym1 (father) + Xf1Xf2 (mother)

could result in Xm1Xf1 (female) , Xm1Xf2 (female), Ym1Xf1 (male) or Ym1Xf2 (male).

Of course the man's X chromosome came from their own mother but the man's Y came from his father; we could got back generation after generation but I don't see how this impacts the original question: Do men favor son's because they completely contribute what makes their sons male but only contribute half of what makes their daughters female. TheFutureAwaits (talk) 10:53, 11 June 2009 (UTC)[reply]

The XY chromosome system is the sex-determination system in most mammals, but not in all animals - birds have an entirely different genetic system (see ZW sex-determination system); some reptiles have a non-genetic temperature-dependent sex determination; some fish and molluscs can even change sex. So in evolutionary terms the Y chromsome is a fairly recent arrival. Even if we stick to mammals, a father contributes more genetic material to his daughters than to his sons (the X chromosome is 153 million base pairs long; the Y chromosome only 60 million base pairs) so an evolutionary argument could predict favouring daughters over sons. OTOH, if there are fewer males than females in the adult population, then a son will produce more grandchildren, on average, than a daughter ... Gandalf61 (talk) 11:02, 11 June 2009 (UTC)[reply]

There are ~25,000 genes that affect a person's physical characteristics, most of which are NOT on the X or Y chromosome. Early in embryogenesis, the gender is completely indeterminate -- males and females all have the same embryonic tissues (Mullerian ducts and Wolffian ducts) that will go on to form the basic internal genital structures through the process of sex determination and sex differentiation. The embryonic genital tubercle and genital folds will develop into the external genital structures. Therefore, you should think of the Y chromosome as having a "switch" (the SRY gene) that turns on a complex genetic program that results in the embryonic gonads becoming testes in a male, whereas the absence of the SRY gene (which is true in XX females but also in Turner syndrome and Swyer syndrome) the default is to form ovaries. Everything follows from that point in development -- testes produce antimullerian hormone that causes regression of the female internal structures, and testosterone that promotes development of characteristic male external genitalia. In the absence of these signals (and probably in the presence of some X-linked gene signals), the system defaults to a female phenotype. Most of the genes that are involved in this process are actually NOT on the sex chromosomes, so would allow contributions from both parents, even though the switch that starts off the process is on the Y. Why would it make sense for the small number of genes on the Y chromosome to be more "selfish" than all the others? There are far more genes on the autosomes. --- Medical geneticist (talk) 11:41, 11 June 2009 (UTC)[reply]

Aren't you overlooking the importance of the SRY "switch"? It seems rather easy to argue gender has a profound effect on many other genes. My hypothesis is that men would favor sons as they are genetically and ultimately phenotypically more related to their fathers versus daughters. The gene/chromosome is exclusive to one parent and has a massive influence on the development of the individual. TheFutureAwaits (talk) 12:05, 11 June 2009 (UTC)[reply]

OK - these explanations have gone WAY off the rails. It's not complicated:

Women have two X chromosomes - men have one X and one Y. The child gets one of the mother's sex chromosomes and one of the father's - but it's random which one. So if the baby is a girl, she got one of her mother's X chromosomes (it's random which one) and the X chromosome from her father. If the baby is a boy - he gets one of his mother's X chromosomes (again, at random) and the Y chromosome from the father. Either way - the kid got one of the two genes from the mother and one from the father so that is no reason to prefer to have a boy child.

Where the confusion lies is that someone here thinks that a girl baby could get both of her X chromosomes from the mother and a baby boy could get both the X and the Y from the father. That's NOT what happens! But if that were the case then in the case of a girl, it would be true to say that there are two possibilities: Both X's from mommy or one X from mommy and one from daddy. There would therefore hypothetically be (on average) 75% of the genetic material in girls coming from the mother and 25% from the father. In the case of a boy - there would certainly have to have gotten the Y from the father but the X could come from either parent - so on average, 75% of the genetic material in boys would come from the father and 25% from the mother. It would then make evolutionary sense for the father to 'prefer' boys to girls because on average they'd contain more of his genetic material. I think that's what the OP imagines. But that's not what happens.

If fathers prefer their boy offspring to their girls (and I'm not convinced of that) - it's more likely to be that it is the traditional role of the father to pass on male-dominated skills (hunting, tracking, boat-building, beer-drinking, whatever) to their sons and for women to pass on traditionally female-oriented skills (nagging, shopping, etc??<shrug>) to their daughters - so it would perhaps make evolutionary sense for the males to preferentially bond with their sons and the females to bond with their daughters. SteveBaker (talk) 12:26, 11 June 2009 (UTC)[reply]

Basically what I said, except alot clearer and alot more complicated...Meh, whatever.Drew Smith What I've done 12:40, 11 June 2009 (UTC)[reply]

As to whether fathers prefer boy offspring, depressingly it seems to be so. Here is a little evidence on the subject. "...if the first child is a boy, the probability of his father leaving the household is 25 percent less than if the first child is a girl." "We find that the birth of a son speeds the transition into marriage when the child is born before the mother's first marriage." However, there are many complicating factors. Interestingly, it seems that the preference-behaviour is shown by people who would say, and probably believe, that they have no such preference. 80.41.126.158 (talk) 19:59, 11 June 2009 (UTC)[reply]

I don't disagree with any of the above but I just want to point out that, unless I'm missing something, evolutionary arguments regarding sex-preference don't add up. The only way a gene causing men to prefer sons would be selected for is if it caused such a strong preference that it made men kill their daughters (or render them infertile somehow). Can such a gene be selected otherwise? Zain Ebrahim (talk) 13:13, 11 June 2009 (UTC)[reply]

Okay, this is getting silly. No one here (at least that I'm aware of) thinks both X's come from the mother. See what I posted above in response to Drew...

Xm1Ym1 (father) + Xf1Xf2 (mother) could result in Xm1Xf1 (female) , Xm1Xf2 (female), Ym1Xf1 (male) or Ym1Xf2 (male).

It seems like a simple misunderstanding but Steve, I would appreciate if you would cross out that section of your discussion since no one is advocating that point of view.

Anyway, what I AM saying is the Y chromosome is ultimately responsible for the creation of a male child. The father is the only one with a Y chromosome and thus 100% responsible for the gender characteristics of a male (XY) child (X from the mother, Y from the father). In the case of a daughter both parents contribute equally to the gender characteristics as one X comes from the mother and one from the father.

Therefore as a father is wholly responsible for the male characteristics of the son but only 50% responsible for the gender characteristics of a daughter it follows that men would prefer sons. TheFutureAwaits (talk) 13:40, 11 June 2009 (UTC)[reply]

The gender is decided by the Y chromosome, but the characteristics are decided by the combination. Let me pose a hypothetical question that may make things a little clearer. What would happen if someone where born with two Y chromosomes?Drew Smith What I've done 14:02, 11 June 2009 (UTC)[reply]

That's not possible, the embryo would fail to develop. XYY can occur but YY can not as there are many genes on X which people require to live. However I am not sure this hypothetical applies to the question... I think the terminology may be throwing people off. Also Drew, can you provide a citation or example for confirmation of your statement "The gender is decided by the Y chromosome, but the characteristics are decided by the combination."?

The male gender characteristics are the result of the activation of a male phenotype by the SRY gene. Therefore what makes a person male and all the male characteristics (not ALL characteristics but those which are unique to males) are caused by the Y chromosome which comes from the father. Does this clear up any confusion on the point I am trying to make? TheFutureAwaits (talk) 14:44, 11 June 2009 (UTC)[reply]

According to The XYY Man he'd be some kind of a super-hero. In reality, he'd have XYY syndrome which I suggest you read. Note that there are also XXX girls...(which, strangely, seem to be advertised a helluva lot in certain parts of downtown Dallas). If you're suggesting someone with two Y chromosomes and no X - they'd certainly never get as far as being born because there are a shit-load of genes on the X chromosome that you can't survive without - so the question is moot. SteveBaker (talk) 14:41, 11 June 2009 (UTC)[reply]

That point of view makes no sense to me. An X chromosome has more genes than a Y chromosome which means that a man actually passes more of his genes to his dauthers than to his sons so, if anything, that naive application of the selfish gene principle would lead to men prefering their dauthers. Dauto (talk) 14:37, 11 June 2009 (UTC)[reply]

Except I'm not refering to the number of genes, but rather to the impact the SRY gene has on the resulting phenotype caused by all the other genes. The Selfish Gene was an earlier work of Dawkins which he expanded on in The Extended Phenotype which may explain a bit more the theory behind my reasoning. Essentially the father has a much greater impact on the phenotype of a son versus a daugther as everything which makes that son male comes from the father. For daughters the contribution is shared equally. TheFutureAwaits (talk) 14:50, 11 June 2009 (UTC)[reply]

"Everything which makes that son male comes from the father" is a trick of language. It has no scientific meaning. The father's genetic material determines the sex of the child, whether male or female. The father supplies 50% of the genetic material whether the child is male or female (slightly less than 50% for a male). That includes 50% of the genes that are preferentially expressed in males and 50% of the genes that are preferentially expressed in females. The mother and father contribute equally to the phenotype of a male child and they contribute equally to the phenotype of a female child. -- BenRG (talk) 15:24, 11 June 2009 (UTC)[reply]

It's about activation, not just numbers. See my responses to Daruto and Looie below. TheFutureAwaits (talk) 16:44, 11 June 2009 (UTC)[reply]

This reminds me of the work by David Haig on Parent–offspring conflict which is related to genomic imprinting and Intragenomic conflict. David D. (Talk) 15:03, 11 June 2009 (UTC)[reply]

Halleujah! This is what I've been getting at the whole time. I can't claim expertise in this stuff though and the articles actually seem a bit sparse, so can anybody explain whether any evidence confirm or contradicts my hypothesis that the father has a much greater impact on the phenotype of a son versus a daugther as everything which makes that son male comes from the father and thus men would prefer sons? TheFutureAwaits (talk) 15:43, 11 June 2009 (UTC)[reply]

Your hypothesis is false. As MedicalGeneticist explained (but maybe in too complicated a way), the things that make a man male are scattered all over the genome. The Y chromosome is tiny, and the main thing it contains is a set of "switches" whose function is to activate the male-related genes on other chromosomes. In females, these genes are present but they don't get activated. The contents of the Y chromosome differ very little across people. Therefore, the mother and father both have essentially equal impacts on the phenotype of a son. Looie496 (talk) 16:16, 11 June 2009 (UTC)[reply]

Yet the switch makes all the difference. When the other genes are not activated then they do not impact the phenotype so ultimately the father DOES make a larger determination. TheFutureAwaits (talk) 16:28, 11 June 2009 (UTC)[reply]

Clearly you're not refering to the number of genes. My point is that you probabily should be refering to the number of genes, unless you can show us that the inheritance of that single gene present in the Y chromosome is more relevant than the inheritance of all the genes present in the X chromosome which you haven't done so far, as far as I can see. Just saying that you are not talking about my point doesn't make it go away, mind you. Dauto (talk) 16:21, 11 June 2009 (UTC)[reply]

See above, it's more important because this gene controls the activation of the other genes you are refering to. If they aren't activated the phenotype doesn't change so ultimately the fact that it controls the activation makes it more important than the pure number of inactive genes. TheFutureAwaits (talk) 16:28, 11 June 2009 (UTC)[reply]

I desagree. I think the fact that it is a simple switch makes it even less important. Prove wrong if you can. Dauto (talk) 16:46, 11 June 2009 (UTC)[reply]

I think it's rather obvious if something has control over a process then it is rather important. Not necessarily more important than the process but in this case it influences the outcome of gender, something the other genes don't do. I would also argue the fact that it alone determines gender makes it extremely important. The differences that result biologically because of gender are very far reaching. TheFutureAwaits (talk) 18:52, 11 June 2009 (UTC)[reply]

Well, I would argue that since all that gene does is determine gender that makes it extremely unimportant as far as it concerns the matter of wheather a father would prefer a son or a dauther. You've simply asserted the oposite point of view but without giving any real reasons for us to accept it. On the other hand I know for a fact that fathers love their dauthers. Dauto (talk) 19:06, 11 June 2009 (UTC)[reply]

Getting back to the original question about "selfish genes" and wanting to pass on one's genes, the idea that a male should prefer sons based on wanting to pass on his genes has been adequately refuted. A male actually passes on slightly more genes to his daughters since the X chromosome carries more genes. Look at the Y chromosome article -- in some species, there are only 4 genes on the Y chromosome. Your argument attaches too much importance to the SRY gene. What if I "hypothesized" that people with orange eyes would rather have children with orange eyes because the "orange eye gene" is selfish? It just doesn't make sense. There are enough social/cultural reasons given for sex preference in offspring that your theory about a genetic basis just doesn't add anything useful. --- Medical geneticist (talk) 17:19, 11 June 2009 (UTC)[reply]

If the SRY gene determines gender then it influences a person's morphology more than pretty much any other gene (yes there are HOX genes but these don't get passed on only half the time). So what I'm saying is it is reasonable the "selfishness" of this gene would be extremely influencial. As a consequence of a gene contributed by only one parent the child's morphology is vastly changed.

If a father has a son everything that makes that son male comes from the father. If a father has a daughter the gender characteristics are cause by both the mother and father. Therefore, a father wishing to pass on his genes would prefer sons as the sons will pass on his male characteristics to their children, daughters will not. TheFutureAwaits (talk) 19:01, 11 June 2009 (UTC)[reply]

A father wishing to pass on his genes would prefer a daughter as the daughter will have more of his genes than a son. Being a male is not that important, really. Dauto (talk) 19:13, 11 June 2009 (UTC)[reply]

This is becoming a circular argument, as I said earlier it's not about the number of genes it's about the end result. Let's try this: do you agree that the gender of a child is determined by the genetic contribution of only the father? TheFutureAwaits (talk) 20:23, 11 June 2009 (UTC)[reply]

No one is arguing that the contribution of the SRY gene is unimportant in determining the gender. It is a critical switch between a male and female phenotype. However, you are incorrect in your assertion that "everything that makes that son male comes from the father". Have a look at the androgen receptor and androgen insensitivity syndrome articles and then tell me whether you still think that the mother does not contribute to the male phenotype in her sons. --- Medical geneticist (talk) 20:48, 11 June 2009 (UTC)[reply]

Androgen receptors are present in men and women; the information is interesting but it doesn't refute the fact that only the contributions of the father determine whether a male is born. The father is solely responsible for whether the switch is triggered and child becomes a boy or a girl. That's where the importance lies; all the genes that interact as a result of this trigger are still dependent on SRY in the first place. TheFutureAwaits (talk) 21:12, 11 June 2009 (UTC)[reply]

I don't think anyone has denied this last statement of yours. What is your point? Tempshill (talk) 22:38, 11 June 2009 (UTC)[reply]

Besides, the genes themselves don't care about the phenotypical outcome as long as they get to be inthe next generation. That's what's meant by selfish gene. And all those genes on the X chromosome are selfish and want to be in the next generation and don't care that much wheather it is a male or a female. The SRY gene is outnumbered and, despite of what you said, I think that does matter. Dauto (talk) 21:30, 11 June 2009 (UTC)[reply]

Going back to the first principles of evolution, suppose a mutation occurs on the Y chromosome being passed on to a son. The son with the mutated Y chromosome has a 50% chance of passing it on to a child; he'll definitely pass it to sons and definitely not pass it to daughters.

Now suppose a mutation occurs on the X chromosome being passed on to a daughter. That daughter has a 50% chance of passing it on to a child; all her children receive an X from her, but only half will receive the mutated X. So both sons and daughters have a 50% chance of giving the mutation to their children. Being on the Y chromosome offers no advantage. --Bowlhover (talk) 03:22, 12 June 2009 (UTC)[reply]

How can you make black through mixing colors?

Hi all,

If you had only primary colors available, would it be possible to mix them together in such a way to make perfect black? (We can assume hypothetically perfect primary colors.) If not, what colors are needed in order to produce perfect black?

Thanks! --Sam —Preceding unsigned comment added by 146.115.120.108 (talk) 13:17, 11 June 2009 (UTC)[reply]

It depends. Are we talking about Addition of Colors? (Like mixing colored light) Or are we talking about Subtraction of Colors? (Like mixing paint). Check out Color mixing to learn the difference. But briefly, if you're subtracting colors, then yes, you can mix ~~red, blue and green~~Yellow, Magenta and Cyan, to form black. But if you're adding colors, then mixing red,blue and green will form white. APL (talk) 13:28, 11 June 2009 (UTC)[reply]

The three primary colors in subtractive mixing are yellow, magenta, and cyan, not red, blue and green. Cuddlyable3 (talk) 20:32, 11 June 2009 (UTC) [reply]

Of course! I knew that. I was ... just testing. APL (talk) 23:43, 11 June 2009 (UTC) [reply]

(ec) In theory, yes, see color mixing#subtractive mixing. In reality, you end up with some kind of dark mud colour because some light is still being reflected. This is the reason printers always use three colours plus black in full colour printing - the "mixed black" is just not good enough for quality documents. SpinningSpark 13:30, 11 June 2009 (UTC)[reply]

Our article is also a little misleading, you might get a nice dark black as shown with subtractive mixing using filters but it won't happen with pigments as the article claims. I might just go edit that. SpinningSpark 13:37, 11 June 2009 (UTC)[reply]

Some inkjet printers can produce a perfectly usable black with only the CMY pigments. APL (talk) 14:03, 11 June 2009 (UTC)[reply]

For additive mixing - mixing light - such as you do on a computer screen - then using zero amounts of the three primary colors gets you black. For subtractive mixing - paint, dyes, etc - you'd theoretically use the maximum amount of all of the primary colors. The problem with subtractive mixing is that firstly, the three primary colors that you'd ideally want are not perfectly manufacturable with available chemicals - and secondly that the means by which dyes, inks and paint pigments work means that they really cannot do a perfect job. SteveBaker (talk) 14:32, 11 June 2009 (UTC)[reply]

I can mix a good subtractive black with clear pigments in acrylic paints. I seldom want flat black because it rarely occurs in nature, but I can mix it. I spent an hour learning how. Most of the time, however, I want black with an edge, a punch, and that means a red-black, a blue-black or whatever suits the painting. // BL \\ (talk) 03:31, 12 June 2009 (UTC)[reply]

Is this person mentally challenged?

Someone online told me a few days ago that the solution to the world's problems was to "have a party for everyone." Now, obviously if you can't diagnosed OPs, you can't diagnose people. :-) But, is this a normal thing for an adult to think? (Okay, I'll admit they may just be saying they're an adult - but you'd think someone pretending to be an adult wouldn't be talking about magically bringing Mideast peace by having a party for everyone.)

What psychological reason would a person have for believing that by jsut throwing a party and inviting everyone, that: A. the people will come; and, B. that they'll put aside so much hatred? I know that in some cases, ordinary citizens have come together peacefully, but that's not the same thing as everyone stopping it.209.244.30.221 (talk) 15:00, 11 June 2009 (UTC)[reply]

Well it worked in south park with Timmy and the bloods and the crips. It would have to be one bitchin' party though. TastyCakes (talk) 15:06, 11 June 2009 (UTC)[reply]

Perhaps he was referring to a party in his mouth in which obviously everyone is invited. It's actual not a horrible idea; a world peace day celebration couldn't cause much harm. TheFutureAwaits (talk) 15:11, 11 June 2009 (UTC)[reply]

Unless someone used it to cover their sneak attack. Then it would just make things worse. I think people make the mistake that all of the world leaders are rational, which may or may not be the case. 65.121.141.34 (talk) —Preceding undated comment added 15:36, 11 June 2009 (UTC).[reply]

This sentiment also embodies the naive assumption that all wars, violence, and feuds are fundamentally "bad" for everybody, and that if we just agreed to stop having wars, violence, and feuds, everyone would be happier. Unfortunately, human history has shown us many times that wars are often beneficial to one or more responsible players. These players have no incentive to stop the war/violence/feud. Most often, they are able to separate themselves from the negative repercussions of conflict, either via force projection, effective defense, or some other method. They can then reap all the benefits while subjected to minimal harm, and are inclined to perpetuate the conflict indefinitely (until some strategic situational change). Nimur (talk) 16:04, 11 June 2009 (UTC)[reply]

Attempting a serious response: People mature psychologically in different ways. Some people may have difficulty formulating a realistic Theory of mind and fail to appreciate the potential threat of coercing various hostile tribes to attend a mass "social" gathering. However, people who voluntarily attend such a gathering would presumably share your friend's hope that we can all get along.

Several political movements have attempted to overcome the inherent fractiousness of human nature, by setting a singular purpose for their followers. Marxism teaches that religion, culture, and ethnicity are secondary to the great historical class struggle for economic justice. Christianity teaches that money, sex and power are secondary to the holy injunction to live a life worthy of Heaven. Secular humanism teaches that autonomy and freedom of thought are among the highest virtues, and the individual actualizes their dreams by hard work and merit. Dictatorships (benevolent or otherwise) demand that the subject peoples submit to the will of the sovereign. All these systems have inherent flaws because humans exhibit behaviour spanning from wonderful atruism to despicable evil.

The only way we can all "just get along" is if/when a large enough proportion of the population decides themselves to do so, through their shared belief and values. Otherwise humanity is always going to be a troublesome collection of competing tribes. ~~ Ropata (talk) 17:50, 11 June 2009 (UTC)[reply]

The OP friend's call to "have a party for everyone" has been interpreted as "throw a party for everyone" which is difficult to do. However if the caller meant "have a political party for everyone" they may be postulating that democracy would solve the world's problems better without political parties. Far from implying mental disease, that is a critical viewpoint that merits consideration. It supports the idea of Direct democracy whereby citizens vote on issues directly without intermediate representatives or parties. Examples of direct democracies are seen in Landsgemeinde in some Swiss cantons and in many countries an occasional referendum (plebiscite) that is held to resolve a specific issue. There are obvious practical difficulties with controlling government this way. However the speaker may have had a more ominous idea that only one political party should be permitted for everyone i.e. a single-party state such as a communist state or a form of fascism. All these are political standpoints that should be open to debate, though inapropriate for this Science desk, but there is a bad precedent for equating dissident political opinion with mental disease. Cuddlyable3 (talk) 20:26, 11 June 2009 (UTC)[reply]

I think the one that works is not "have a party for everyone" but is "everyone has a party together and likes it" but that won't feed people who are hungry :( ~ R.T.G 20:28, 11 June 2009 (UTC)[reply]

Well I would assume this party has snacks and drinks, but yeah long term, they still have no food. And on a more serious note, you would have a very difficult time hosting a party for everyone on earth not only logistically, but also without gravely insulting at least one group. That means, your catering can have no alchohol or you will insult the Muslims, no pork products for the same reason. No beef because of Hindus. In fact, better go no meat at all for the vegans. Now you upset just about everyone else who was hoping for some beer and pizza. My point is that if you can't even get the catering to work out for all these groups, how do you expect them to work more serious issues out? I do not know this person and can not tell if they were serious, but they appear to be hopelessly idealistic. 65.121.141.34 (talk) 20:50, 11 June 2009 (UTC)[reply]

The best part about throwing an everybody-in-the-world party is that there are no neighbors to complain about the noise. APL (talk) 21:02, 11 June 2009 (UTC)[reply]

A fair amount of the world doesn't drink, would this be a dry party? TheFutureAwaits (talk) 21:17, 11 June 2009 (UTC)[reply]

Back to te original question. I doubt the person was serious. However, taking the question at face value, and assuming they were serious, I would have to say that, yes, this person is perfectly sane, but most likely wrong. There are many mature, rationale, successful (have an apartment and car) adults who would do nothing but party if given the chance. Now how many of those people are in politics? :)

On a side note, war is not a bad thing. War distracts countries from developing dangerous technologies. War boosts the economy. War keeps the population under control. War is an outlet for aggression. Without war, society would collapse. Now bring on the insults and rebuttals, because I know they are coming.Drew Smith What I've done 03:44, 12 June 2009 (UTC)[reply]

Rebuttal... Wars are excellent routes for technological advances. No one cares about the money you are spending on it, and you have a very strong motivation to develop new stuff to get the bad guys. 65.121.141.34 (talk) 13:19, 12 June 2009 (UTC)[reply]

God forgive me but you pluck ones out to represent all of the differing opinions/religions etc. but you make sure 100% they will not kill or even badly injure each other ever. You put them all on a spacecraft like the Arthur C Clarke Rama with all they need to sustain themselves or party and tell them they are going to a far away star. Then just throw them into orbit and watch them like Big Brother. You have picked them all out correctly so none dominates, none suffers too severe depressions, competitiveness is mild and the environment gets adequate care (which means excellent care really). You sit back and watch them all and they instinctively produce the solution to human differences. Maybe thats what the Earth is already. ~ R.T.G 15:33, 12 June 2009 (UTC)[reply]

How do you select them so that you know that they will never kill or intentionally injure each other? I suspect even the Amish (about as pacifist a group I have ever seen) probably have the rare murder. 65.121.141.34 (talk) 16:37, 12 June 2009 (UTC)[reply]

WW2 was a good motivator for scientific progress, but is that typical of all wars? WW2 was a special case in many ways. For example, what technological advances has the civil war in Darfur produced? APL (talk) 18:46, 12 June 2009 (UTC)[reply]

You mean Darfur Sudan??? Probably because everyone else did the technological advances that they are using in their war 20+ years ago. 65.121.141.34 (talk) 19:53, 12 June 2009 (UTC)[reply]

Ah! selecting them is the trick, I couldn't let you in on that. ~ R.T.G 20:52, 12 June 2009 (UTC)[reply]

Hey, doesn't this discussion belong on the Humanities desk instead? 76.21.37.87 (talk) 03:47, 14 June 2009 (UTC)[reply]

Probably a combo of science and humanities. Anyway my comment on distracting countries from developing dangerous tech was a little misleading. Example: the A bomb would have been completed a lot sooner if not for WW2. The war diverted valuable funding away from the manhatten project.Drew Smith What I've done 03:54, 14 June 2009 (UTC)[reply]

Quick one on Darfur; There was a truck discovered with a modifyed suspension so it didnt bounce so much when it was mounted with a Dushka and used as a platform for a fire baseChromagnum (talk) 10:37, 17 June 2009 (UTC)[reply]