Wikipedia:Reference desk/Archives/Science/2009 July 18

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July 18

Car incident types

Quotation: "Lane change accidents are noted as one of commercial vehicle fleet's top 3 accident types." Anyone know(or at least can guess) what the two others accident types? Vitall (talk) 04:39, 18 July 2009 (UTC)

Rear-enders are the most common kind of car crashes, I'm sure of that. WP:OR: I've myself been rear-ended twice within a year or so, once by an 18-wheeler (OUCH!!!) and the second time by a jeep. FWIW 76.21.37.87 (talk) 05:02, 18 July 2009 (UTC)

There would of course be more than one way to define "accident type". However, from page 31 of this document, it looks like rear ending is indeed the most common accident type, and the second most common is hitting a fixed object. The referenced document lists the third most common accident type as “side swipe (opposite or same direction)”, which does seem like it would include a typical lane change accident. Red Act (talk) 08:52, 18 July 2009 (UTC)

... which clearly indicates that roads are too short rather than too narrow ...  ;-) 93.132.138.254 (talk) 16:49, 18 July 2009 (UTC)

Miscarriage question

First, I am a regular user, but for obvious reasons I am not logging in to post this question. Second, I am not asking for medical advice, but for artices (WP or other) relating to the question.

A few years ago I was with a girl who was a frequent liar. The first time she claimed to be pregnant I was 16, and believed her. About a month later she claimed to have had a miscarriage. I believed her. The second time, I was probably 17. I wasn't so sure about it this time. Soon after she claimed to have had another miscarriage. This happened a few times more, and by the time I left her I didn't believe that she had ever been pregnant.

Now, my current girlfriend is going through a miscarriage. At about 4 weeks into the pregnancy.

Now I'm wondering if my first girlfriend may have been telling the truth, and the miscarriages are somehow related to me. Is there any connection between males and miscarriages?75.93.119.255 (talk) 05:45, 18 July 2009 (UTC)

I'm not an obstetrician, so please don't take this as medical advice, but the only way a male could present a risk factor for miscarriage is if he's a heavy smoker (if he smokes more than 2 packs a day, then his wife / girlfriend could be up to 3 times more likely to have a miscarriage). However, if you're not a heavy smoker, then there's no conceivable link between you and your current girlfriend's miscarriage. In this latter case, the current miscarriage is not your fault (or hers, for that matter), and your first (ex)-girlfriend is a damned rotten liar. FWiW 76.21.37.87 (talk) 06:47, 18 July 2009 (UTC)

From personal experience here: having had at least 5 misses myself, and talking to doctors about why, it seems that about 50% of all pregnancies end in miscarriage: sometimes the period is just a few days late but there is still a pregnancy which has ended. So don't blame yourself for this. It's a natural feature of being a woman. Oh - and you may wish to consider using contraception to prevent pregnancy and therefore miscarriage occurring in future. --TammyMoet (talk) 08:32, 18 July 2009 (UTC)

I'm also not an obstetrician but I would have to disagree with 76. There's no reason why a male can't be a factor in miscarriages. If the miscarriages are caused by genetic defects (e.g. chromosomal abnormalities), then that could be either the male or the female. E.g. [1] [2] [3] [4]. Also there's no way we can know that 'your first (ex)-girlfriend is a damned rotten liar' as 76 suggested. Even if you aren't a factor, it easily possible your ex-girlfriend had a fertility problem of her own. I woulld also emphasise TammyMoet's point. Miscarriages are hardly uncommon and probably more common at such a young age as your first relationship (although 4+ is fairly unlikely without some sort of problem, that could still go away naturally). And if you don't want to have a baby, you need to look at more efficient contraception since it sounds like whatever you've been doing hasn't been working. And finally, if you are concerned about your fertility, you should see a specialist. Nil Einne (talk) 10:14, 18 July 2009 (UTC)

OK, I take back the "damned rotten liar" part. However, if there are 5 miscarriages in a row, it's highly unlikely that genetic defects are a factor in all of them. No, 75 IP's genes can almost definitely be ruled out as a factor, so assuming that 75 IP is not a heavy smoker (which would be a factor) and that his first ex-girlfriend was telling the truth (which she might or might not have), then it would mean that she had an infertility problem of her own (as Tammy pointed out) and that the current miscarriage was simply a random misfortune. So, to recap: if 75 IP is a heavy smoker, he should quit smoking or at least cut back to less than a pack a day; if not, then he is not a factor in his girlfriend's miscarriage.

76.21.37.87 (talk) 00:12, 19 July 2009 (UTC)

Well, just to be a smartass, it doesn't appear that I need any contraceptives. But everything else makes sense. And it was 4 in 2 years. 6, if you count both sets of twins she claimed... Now you understand why I didn't believe her. Still don't, but I'm wondering if maybe one of them was real...75.93.119.255 (talk) 10:54, 18 July 2009 (UTC)

Carriers of a Balanced translocation can be at high risk to have a fetus with an unbalanced chromosome content thus leading either to frequent miscarriages or children with disability. If the information you were given by your partners is correct then I would follow Nil Einne's recommendation to see a specialist. --- Medical geneticist (talk) 11:53, 18 July 2009 (UTC)

I know you're being a smartass but believe me, miscarriages are not trivial, and indeed carry risks to the health of the mother. If you do have something wrong with you which causes your progeny to spontaneously abort, the least you could do is prevent the pregnancy occurring in the first place. And you'll not find out if there is something wrong until you see a specialist. Have some common decency man! --TammyMoet (talk) 12:35, 18 July 2009 (UTC)

Looks like he's one of those people who don't have to work themselves for the money there offspring needs, not to mention other care. 93.132.138.254 (talk) 15:43, 18 July 2009 (UTC)

This is 75.93.119.255. Just for the record, my second girlfriend already had a baby when we started dating. And I worked my ass off to provide for them both. Please remove the personal attack, it was highly uncalled for.Drew Smith What I've done 22:18, 18 July 2009 (UTC)

Twins are usually diagnosed by ultrasound, somewhere between 14 and 20 weeks. A miscarriage at that stage is serious, often requires hospitalisation, and would be hard to miss by anyone seeing the patient on a nearly daily basis. Girls whose periods are not totally regular may imagine themselves to be pregnant for a few days' lateness, then imagine a miscarriage when the period does start. An amount of wishful thinking may also involved. together with testing out the reactions of boyfriends and family.

There seem to be slightly more miscarriages of male foetuses where an earlier pregnancy (completed or not) was also male. - 220.101.166.151 (talk) 03:12, 19 July 2009 (UTC)

I don't see how you can rule it out. As MG has said, there is at least one condition, and probably more which can lead to frequent miscarriages (and of course if the child is born, it's likely to be suffering some sort of nasty condition). Perhaps you are under the mistaken presumption we're talking about 5 random events. Clearly we're not. We're obviously considering a defect that exists in the germline (whether because of a mutation that arose early on in development or whether it also occurs in the somatic cell line and the OP is a carrier of the condition is irrelevant) and therefore would be present in many or all sperm. It's also worth remembering we may not be talking about an all or nothing situation here. It's possible some of the miscarriages were genuine and some weren't (e.g. it's easy to imagine that if say the first two were and because of the effect they had, the person then made up the next few cases (obviously the person would still be a liar in that case). What case is the most likely is speculatory so not really for the RD but my point being there's ultimately a lot of possibilities. N.B. If you are uncertain if it's worth seeing a specialist, and you still know how to get in to contact with the ex, it may be worth explaining the situation to them making clear why you want to know and that you have no intention of telling anyone else etc to try and find out the truth about these previous alleged miscarriages. Nil Einne (talk) 17:31, 19 July 2009 (UTC)

It could still be that his first girlfriend had an infertility problem of her own, which would explain the first 4 miscarriages and leave only the last 1 as a "random event". Or maybe smoking was to blame after all -- I know that the OP smokes tobacco (see "Cigarettes against tear gas"), don't know how much. (BTW, it's only likely to be a factor if it's more than 1 pack a day.) Or perhaps his first girlfriend WAS a dirty rotten liar and lied all 4 times about having a miscarriage, which would also explain a lot. FWiW 76.21.37.87 (talk) 01:20, 20 July 2009 (UTC)

Yes, I smoke alot now, but not when I was with the first girl. I guess it's still more likely to be a coincidence. If it happens with the next girl though, I'm seeing a doctor.Drew Smith What I've done 05:20, 20 July 2009 (UTC)

I’m rather shocked this question hasn’t been deleted yet.

Some pertinent information from this page: Repeated miscarriages are one of the signs that a miscarriage may have been due to genetic defects passed on by a parent. The source defines “repeated” miscarriages as being three or more miscarriages. Only 1 in 200 women have repeated miscarriages. Another sign that a miscarriage may have been due to genetic defects passed on by a parent is if a parent has a child or relatives who have birth defects. Genetic testing (I presume meaning of the parents) can help the doctor identify the problem.

In my opinion, what we should really be saying here is “See a doctor.” Red Act (talk) 11:03, 20 July 2009 (UTC)

"Second, I am not asking for medical advice, but for articles (WP or other) relating to the question."Drew Smith What I've done 09:22, 21 July 2009 (UTC)

In that case, the article "Miscarriage" should have the info you're looking for. 76.21.37.87 (talk) 23:26, 21 July 2009 (UTC)

Can all animals store fat?

And if so, is it possible for any animal to become obese? ScienceApe (talk) 07:20, 18 July 2009 (UTC)

All vertebrates can store fat, and cats in particular can become obese (I don't really know about other animals). FWiW 76.21.37.87 (talk) 07:41, 18 July 2009 (UTC)

Of course they can, labradors (dogs) tend to fattyness, bears store fat for hibernation, etc etc.83.100.250.79 (talk) 11:18, 18 July 2009 (UTC)

I don't know about "of course". I don't know if you can find obese locusts, for example. Or overweight sponges. Vimescarrot (talk) 11:53, 18 July 2009 (UTC)

Sorry, my mistake - I didn't notice it said "any animal".83.100.250.79 (talk) 11:58, 18 July 2009 (UTC)

Also, bears might not hibernate. The Book of Animal Ignorance says it's "torpor"; our article on that says torpor is hibernation, but there's still some debate as to whether black bears do it. Though you're right, they do layer up fat before they do it. </trivia> Vimescarrot (talk) 11:57, 18 July 2009 (UTC)

Fish etc don't become obese as mammals do. (Actually some sites say fish can become obese - but I'm not sure - they can develope poor morphology due to lack of exercise - but I'm not sure about 'obese' )83.100.250.79 (talk) 12:15, 18 July 2009 (UTC)

Ants cannot become obese because their exoskeleton prevents them from doing so.83.100.250.79 (talk) 13:01, 18 July 2009 (UTC) However they can store fat [5] 83.100.250.79 (talk) 13:04, 18 July 2009 (UTC)

Hmm... seeing how much fat ants can actually store would make an interesting research project for some entomology graduate student. I can see the paper now: "subjects were fed Snickers (Mars Incorporated, Hackettstown, NJ) three times daily..." – ClockworkSoul 15:19, 18 July 2009 (UTC)

Even the humble Amoeba can slow the signs of obesity

If specimens of Amoeba proteus are fed exclusively on colpidia, they become very large and extremely fat and sluggish ..[6]

They can store energy as glycogen or fat:

Fat and glycogen are two distinct types of storage material present in Amoeba proteus[7]

83.100.250.79 (talk) 13:40, 18 July 2009 (UTC)

Amoeba are protists, not animals. DRosenbach ^{(Talk | Contribs)} 19:46, 19 July 2009 (UTC)

There are some fish whose flesh contains hardly any fat at all -- haddock and cod, for example, are less than 1% fat. So, although I don't know for sure, I doubt that those animals would be able to store fat to any significant degree. Looie496 (talk) 05:36, 19 July 2009 (UTC)

What about Jellyfish? -- penubag  (talk) 06:25, 19 July 2009 (UTC)

The answer would be no -- obesity does not manifest in all types of animals. Unless by any, you did not meant to specify a universal generatlization that all animals can present as obese, but rather can any (at all) animals (i.e. non-humans) become obese, then the answer would certainly be yes. DRosenbach ^{(Talk | Contribs)} 19:46, 19 July 2009 (UTC)

So what happens when a Jellyfish or ant consumes a large amount of food or overeats so to speak? ScienceApe (talk) 03:55, 21 July 2009 (UTC)

Irreducibility of multivariate polynomials

I cannot find anything about that. I can think of two reasons for this: either it's utterly complicated and not well understood or it can be so easily reduced to the question of irreducibility of polynomials of a single variable that no one cares to tell. What is it? 93.132.138.254 (talk) 09:35, 18 July 2009 (UTC)

Wikipedia:Reference_desk/Mathematics#Irreducibility_of_multivariate_polynomials

You really should ask on the maths desk - I've copied your question to there.83.100.250.79 (talk) 11:20, 18 July 2009 (UTC)

I haven't ever got a useful answer there... 93.132.138.254 (talk) 14:46, 18 July 2009 (UTC)

Then ask for more explanations and details. - on the maths desk - because it's a maths problem.

Also try waiting a bit.83.100.250.79 (talk) 16:45, 18 July 2009 (UTC)

It's a math problem, yes. But on the IT desk and on the math desk are the people who are posing questions --- here on the science desk are the people who read questions: for fun, to broader their horizon, and, in regard of the previous, as kind of a nearly effortless side effect, help with ideas and answers. That's the difference I can't ignore. But when there is no more of an answer than "go and learn some math" then I see there's no place to put those kind of questions and it's only a waste of time. And I won't ask about what is meant be "leading term" in the article of Gröbner basis, not here nor there. 93.132.138.254 (talk) 17:29, 18 July 2009 (UTC)

1. Yes, multivariate factoring is complicated.
2. Yes, the math desk is the right place to ask.
3. Wikipedia's coverage of symbolic algebra is actually not all that good (compared with other math subjects), but a google search for "multivariate factoring" may help you get started. 67.117.147.249 (talk) 00:59, 19 July 2009 (UTC)

Gravity

Did Newton have a theory for gravity, or did he just create a law for it? If Newton didn't, does that make Einstein the only one with a theory for gravity? --wj32 ^t/c 09:47, 18 July 2009 (UTC)

There isn't any difference between what you are saying. There isn't any difference between a 'law' and a 'theory' in science, there are only mathematical relationships that can be used to accurately predict outcomes. —Preceding unsigned comment added by 58.111.132.76 (talk) 09:55, 18 July 2009 (UTC)

No, a law is a statement whereas a theory is an explanation. If those aren't the definitions, then that's what I'm asking anyway. --wj32 ^t/c 11:03, 18 July 2009 (UTC)

If you think of a law as a mathematical framework to compute things, say F=Gm, and of a theory as a deeper (whatever that is) framework that helps to understand (whatever that is) how an effect comes to exist (say, you describe chemical bonds using the laws for the electrical field), then neither Newton nor Einstein did have a theory. The first puts in the mass, not understanding what this really is, the other puts in curvature of space-time, not explaining where this comes from. But the distinction is rather artificial and subjective. 93.132.138.254 (talk) 10:22, 18 July 2009 (UTC)

I get what you're saying, but then is there any possible way for gravity to have a "theory" behind it, since it's a fundamental force? --wj32 ^t/c 11:06, 18 July 2009 (UTC)

The distinction between a scientific law and a theory has rather vague, subjective boundaries, and part of the difference is just that the term “law” was more popular historically, and “theory” is more popular now. However, Einstein’s general theory of relativity is arguably more of a theory than Newton's law of gravity, in that there’s more of explanation given as to what is going on. Newton’s law of gravity, to modern eyes at least, is not much more than one equation, with a definition of what each of the terms in the equation is. General relativity consists of not only Einstein’s field equations, but the explanation that those field equations are describing how the stress-energy tensor causes a curvature in spacetime. But part of that difference is just a subjective matter of perspective. The fact that spacetime is curved is very unobvious, so Einstein’s explanation seems quite important. However, in Newton’s day, the explanation that every two point masses might attract each other was also a very unobvious observation. So they are arguably both theories. Red Act (talk) 11:23, 18 July 2009 (UTC)

OK, I guess it is a subjective thing, then. Thanks for the explanation. --wj32 ^t/c 11:28, 18 July 2009 (UTC)

All that people mean when they call gravity fundamental is that we don't currently explain it as a consequence of something else, not that we won't ever do so. Newton famously refused to speculate about the mechanism of the gravitational interaction (hypotheses non fingo), but I think he believed there was some mechanism because he didn't believe in direct action at a distance. In a way general relativity provided that mechanism by explaining Newton's action-at-a-distance law as a consequence of a (rather different looking) local law. It's not clear we should use the name "gravitation" for both. Newton's law of gravity wasn't the first either. The first law of gravity was the observation that things fall to the ground of their own accord, which must predate recorded history and probably even H. sapiens. Newton's discovery was universal gravitation, which is the fact that the same force that makes things fall to the ground is also responsible for the motion of the planets. In a sense by carrying the name "gravity" from one phenomenon to another we've decided by fiat that there will always be something fundamental called "gravity". -- BenRG (talk) 11:34, 18 July 2009 (UTC)

(After edit conflict) Newton deduced the law of universal gravitation and used it to explain and connect a variety of other phenomena, including the motion of the Moon, tides and Kepler's laws of planetary motion. He also proposed at least two different explanations for the origin of gravity itself - see Mechanical explanations of gravitation#Streams - but ultimately realised that these explanations were unsatisfactory. In 1713 he added the famous Hypotheses non fingo statement in an appendix to the second edition of the Philosophiæ Naturalis Principia Mathematica: "I have not as yet been able to discover the reason for these properties of gravity from phenomena, and I do not feign hypotheses". We still do not have a satisfactory "theory of gravity" in the sense of a deeper explanation that connects it with the other fundamental forces - although there are various candidates for the position. Grand unification theory successfully combines the other three fundamental forces within the Standard Model, and the search for a "theory of everything" that incorporates gravity within this framework is one of the biggest unsolved problems in physics. Gandalf61 (talk) 11:41, 18 July 2009 (UTC)

See Universal_gravitation#Newton's_reservations

Principia: "I have not yet been able to discover the cause of these properties of gravity from phenomena and I feign no hypotheses... It is enough that gravity does really exist and acts according to the laws I have explained, and that it abundantly serves to account for all the motions of celestial bodies

The same section also metions that he did "..invented two mechanical hypothesis in 1675 and 1717" - though it seems he wasn't happy with them - so he had guesses at theoretical origins of gravity, but nothing he was satisfied with.83.100.250.79 (talk) 11:47, 18 July 2009 (UTC)

It's obvious to me that the questioner is asking if newton had a hypothesis for the origin of the gravitational force (and by extension the form of the force/distance equation) - as such "Newton's aether-stream hypothesis" seems to be one of them - it doesn't seem (though I may be wrong) that he accepted gravity as a fundamental force, and would have wished to explain it in terms of some motion (ie an explanation via the laws of motion )at least that's what I think is the case83.100.250.79 (talk) 11:52, 18 July 2009 (UTC)

I can't find much more on it though this article [8] might help a little.83.100.250.79 (talk) 11:55, 18 July 2009 (UTC)

Newton's theory of gravity was that there was an force called Gravity. He had no explanation of what caused it on a physical level. He postulated that there was a thing called Gravity, it existed, and it could be understood with his equations. He was roundly criticized in his time for postulating an "occult" force, something that wasn't based in other known natural properties. Over the years of course people assimilated the force of gravity into their understanding of the natural properties of the universe, which is why we find it so unproblematic today, even though the Einsteinian explanation gets rid of the force altogether and makes it all a question of the path of least resistance in spacetime. --98.217.14.211 (talk) 14:15, 18 July 2009 (UTC)

The way I always distinguish: A scientific law is the simple equation, like V=IR or U=GMm/r. When you plot your data, you get a cluster of points around the "law", and a least-squares fit will re-derive the law. A "scientific theory" is the technique you use to pick which law you need to plot. Nimur (talk) 00:40, 22 July 2009 (UTC)

infertility

how infertility occurs? —Preceding unsigned comment added by Shrekul (talk • contribs) 11:24, 18 July 2009 (UTC)

Infertility#Causes will get you started.83.100.250.79 (talk) 11:40, 18 July 2009 (UTC)

How far can people shout?

How far can the average human shout? I've checked the Vociferation article and it says the maximum audio levels but I'm not sure how to work out the distance that people could hear them, nor how loud the average person is. 92.233.244.115 (talk) 12:21, 18 July 2009 (UTC)

I can't find anything about it online but in one of my From Our Own Correspondent it talks of people in (I think) Spain that had a language that they'd shout across mountains to each other. It has be to a number of miles, but the environment will be the biggest factor - plus it depends on whether you count using 'nature' to amplify you or not? After all in some building in London (St Pauls Cathedral? You can whisper along the edge of the wall and it will move round the build and the person on the other side will hear you. ny156uk (talk) 17:00, 18 July 2009 (UTC)

Infact we have an article Whispering gallery. Nothing to do with 'furthest' but shows how important the environment is to the range. ny156uk (talk) 17:02, 18 July 2009 (UTC)

From [9] you can see Australia's loudest shout (Done by a crowd) can do 115.8 decibels. When you double the distance you reduce the intensity by 1/4, but since decibels is logorithmic, this works out to be ~6 decibel reduction for each time the distance is doubled. 0 Decibels is considered the threashold of hearing, so the distance can be doubled 115.8/6.02=~19.234. This gives us a distance, in perfect conditions, of 2^19.234=~616,595 meters (since I'd assume the originally measured amount of decibels is at a length of 1 meter, but I couldn't verify this). So we get 616 km or 383 miles. Obviously this could never occur in the real world since you can't hear something of 0 decibels over even the faintest noises of wind. 100 miles may be more reasonable for a real world max. I've seen reports of people shouting across lake Michigan (can't find source now) which is 60 miles across in most areas, but I'm not sure the distance where the guy shouted was. Anythingapplied (talk) 17:48, 18 July 2009 (UTC)

My somewhat dated (1990) copy of the Guinness Book of World Records, on page 33, says

"The normal intelligible outdoor range of the male human voice in still air is 200 yards. The silbo, the whistled language of the Spanish-speaking Canary Island of La Gomera, is intelligible across the valleys, under ideal conditions, at 5 miles. There is a recorded case, under freak acoustic conditions, of the human voice being detectable at a distance of 10 ½ miles across still water at night. It was said that Mills Darden (see Heaviest Men) could be heard 6 miles away when he bellowed at the top of his voice."

As far as shouting across Lake Michigan, I think you’re thinking of being able to see across Lake Michigan under unusual circumstances, as in the article quoted in this post[10]. (I never thought I’d use the Flat Earth Society as a reliable source, but they’re copying a now-unavailable Holland Sentinel article verbatim.) Red Act (talk) 21:37, 18 July 2009 (UTC)

There were people whose duty it was to wake up those who were on duty in the Temple in Jerusalem [Mishnah: Shekalim 5:1]. The noise that they made was so loud that King Agrippas said it could be heard as far away as 32 kilometres [Jerusalem Talmud: Shekalim 5:1] or according to another version 12 kilometres away [Babylonian Talmud: Yoma 20b]. Simonschaim (talk) 11:42, 19 July 2009 (UTC)

Oh, that’s nothing. When Athena was born by emerging fully grown and fully armed from Zeus’ head (after Zeus had swallowed Athena’s pregnant mother), she gave out a shout that echoed throughout the whole world.[11]. That beats the heck out of those Jerusalem shouters! Red Act (talk) 15:11, 19 July 2009 (UTC)

I don't know about Athena, but from what I gather (WP:OR), Valkyries can shout really loud too... :-) 76.21.37.87 (talk) 00:45, 20 July 2009 (UTC)

Apollo Lunar Rovers

Are these vehicles visible on the moon through Earth-based telescopes? —Preceding unsigned comment added by 76.195.3.170 (talk) 16:41, 18 July 2009 (UTC)

Nope. -- Aeluwas (talk) 17:53, 18 July 2009 (UTC)

They're not on any of the recently released LRO images http://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/apollosites.html, but those look to be able to resolve them. I don't know if they were parked so close to the lander that LRO can distinguish them. 87.114.153.140 (talk) 18:13, 18 July 2009 (UTC)

Maybe they were carjacked and taken to a chop shop. Edison (talk) 19:54, 18 July 2009 (UTC)

ROFLMAO! X-D 76.21.37.87 (talk) 00:16, 19 July 2009 (UTC)

The LRO images that were released a few days ago are said to be only about a third of the resolution that the LRO will achieve when it's fully operational - from the look of the present photos - I think that spacecraft will be able to resolve the rovers - but you aren't going to see much - one or two fuzzy pixels maybe. Earth-based telescopes don't have the resolving power to image even the landers - the rovers are quite a bit smaller than the landers. SteveBaker (talk) 23:41, 19 July 2009 (UTC)

How well known was the gravitation of the moon?

The article gravitation of the Moon states that the acceleration due to gravity near the surface of the moon is about 1.63 m/s^2. When was this determined? Specifically, before the moon landing, had the moon's gravitation been correctly predicted? --bdesham ★ 19:07, 18 July 2009 (UTC)

Interestingly, you don't need to know much to calculate an approximation: Newton's law of universal gravitation says gravity near a massive object only depends on its mass and the distance from it.

1. If you know the earth's gravity and diameter, you can calculate its mass.
2. If you know the mass of the earth and the orbit of the moon, you can calculate the moon's mass: Planetary_motion is also governed by the same gravitational laws.
3. If you know the moon's mass and diameter, you can calculate the approximate gravity at its surface.

Now this all assumes the moon is approximately homogeneous, which we know is only sorta-approximately true (the article you linked talks about variations and their causes, and the very first sentence talks about mapping from orbit...did we send orbital probes before landing missions?), but if we're talking just a decimal-place or two and "average" "near the surface", seems a reasonable guesstimate. DMacks (talk) 19:34, 18 July 2009 (UTC)

Please help me out here. You state "If you know the mass of the earth and the orbit of the moon, you can calculate the moon's mass." OK, consider a satellite in a circular orbit 10000 miles above the Earth. What is its mass? Is there more info in "orbit of the moon" than I am seeing? Edison (talk) 19:53, 18 July 2009 (UTC)

I meant to ask "What is the satellite's mass?" There can be a satellite in orbit at the same height as the International Space Station with 1/1000 of its mass. The orbital height of the satellite tells you nothing about its mass, does it? Edison (talk) 01:28, 19 July 2009 (UTC)

Knowing the earth's gravity and diameter doesn't get you the earth's mass, it gets you the earth's mass times the universal gravitational constant (which is itself hard to measure). And how does the orbit of the moon allow you to calculate the moon's mass? You can use it to get GM_earth, but that's all I can see. Algebraist 20:12, 18 July 2009 (UTC)

The distinction between the case of an artificial satellite and the moon is one of mass. While for very nearly all intents and purposes an artificial satellite has an utterly negligible mass when compared to the Earth, the moon masses a little bit more than 1% of the mass of Earth. For a circular orbit, the orbital period (T) is related to the orbital radius (r), the gravitational constant (G), and the two bodies' masses (M and m) by the relation

T² = 4π²r³ / G (M + m)

(See also Standard gravitational parameter.) For artificial satellites, M >>> m, so we usually just drop the mass of the satellite and assume a constant orbital velocity at a given altitude. For the moon, the apparent orbital period will be just a trace shorter than it 'ought' to be under that assumption; the discrepancy can be accounted for by the moon's mass. TenOfAllTrades(talk) 20:26, 18 July 2009 (UTC)

Of course, I'd forgotten that trick. That gives you the moon's mass in terms of the earth's mass, and you can calibrate the earth's mass with earthbound measurements of G. Algebraist 20:53, 18 July 2009 (UTC)

Indeed (@Algebraist), "Knowing the earth's gravity and diameter[...]gets you the earth's mass times the universal gravitational constant", which if we assume is a constant we just look up in some well-refereed publication that is reputed as being usable for the types of calculations at hand. If we use the same constant in all calculations, seems like we'll be good for comparison to earth's gravity (the original question) even if the absolute intermediate values (e.g., "mass of earth")aren't as correct. DMacks (talk) 20:42, 18 July 2009 (UTC)

Actually, I'm fairly sure all of the steps above can be done knowing only the products GM and Gm. For the question being asked I don't think it is necessary to know G or M by itself. One of the reasons G is so hard to measure is that you can only get at it when comparing gravitational forces to non-gravitational ones. Dragons flight (talk) 05:00, 19 July 2009 (UTC)

Okay, so we can determine GM_Earth from surface gravity on Earth and radius of the Earth, both of of which are known very accurately. And in principal we can determine G(M_Earth + M_Moon) from the period and semi-major axis a of the Moon's orbit. Then we subtract GM_Earth fromG(M_Earth + M_Moon) to find GM_Moon. Problem in practice is that GM_Moon is only about 1% of GM_Earth, so to find GM_Moon to an accuracy of, say, 1% you need to know G(M_Earth + M_Moon) to an accuracy of 0.01%, and so you need to know the semi-major axis a of the Moon's orbit to an accuracy of about 0.003% (because G(M_Earth + M_Moon) is proportional to a³). In other words you need to know the semi-major axis of the Moon's orbit to within about 10 km. In a pre-spaceflight era, that seems like a big challenge. Gandalf61 (talk) 09:14, 19 July 2009 (UTC)

Yep, that's a tough measurement, and I can't think of a clever way to get it. (I can't guarantee that they didn't have one, but it seems unlikely.) I did a bit of poking around, and found that Michelson (of Michelson-Morley) and Gale did some experiments around World War I that aimed to directly measure the tidal force of the Moon from the Earth's surface. Morley did some painstaking measurements with some cast-iron pipes and microscopes, and was able to derive an estimate of the Moon's mass: [12][13][14]. The number he came up with was about 30% low, but it was a remarkable achievement given the magnitude of the effect he was measuring.

Another approach would be to try to locate the barycenter (center of mass) of the Earth-Moon system. The ratio of the Earth-barycenter and moon-barycenter distances tells you the ratio of the two bodies' masses. Unfortunately, the wobble that puts into the Earth's orbit is only about 3000 miles/5000 km to each side, and the Earth orbits the barycenter at only about 10 meters per second. I'm not sure if there's any clever way to make those sorts of measurements with pre-spaceflight technology.

Per Dragons flight below, there were of course several missions that orbited or flew by the moon years before there were actual landings; highly precise measures of the moon's mass would have been easily derived from those flights. TenOfAllTrades(talk) 13:58, 19 July 2009 (UTC)

With Newton's insights into the nature of gravity, the rough radius of the moon, and an assumption that the moon is made of rock, an 18th century scientist could get the right answer within 20% or so. More directly there were several lunar orbital missions before the lander missions, so the gravity would have been well known before any human set foot on the moon. Dragons flight (talk) 13:35, 19 July 2009 (UTC)

Cute bug

Can anyone recognize the the bug shown [15] here? Photo was taken a couple of days ago in Connecticut. RJFJR (talk) 20:09, 18 July 2009 (UTC)

It appears to be the larva of the Spicebush Swallowtail, Papilio troilus.CalamusFortis 20:24, 18 July 2009 (UTC)

(after ec) Yes, Papilio troilus larva it is. --Dr Dima (talk) 20:28, 18 July 2009 (UTC)

Thank you. RJFJR (talk) 21:14, 18 July 2009 (UTC)

As a matter of interest, are the caterpillar's markings intended to mimic a snake's head/face? --Kurt Shaped Box (talk) 00:15, 19 July 2009 (UTC)

Yes, most likely a head of a predator. It doesn't really matter whether it looks more like a snake, a tree-frog, or a lizard; it reduces a chance of being attacked and eaten all the same. Big eyes + big mouth = danger = do not approach. --Dr Dima (talk) 00:48, 19 July 2009 (UTC)

TBH, I'd be wary to approach that if I saw it in my garden without knowing what it was. --Kurt Shaped Box (talk) 02:05, 19 July 2009 (UTC)

Some research was performed on the larval markings of this species, and it was determined that the false eyes deter predators because, no matter what angle they are viewed at, like the eyes of the Mona Lisa, they appear to follow you.CalamusFortis 03:08, 19 July 2009 (UTC)

WQ Test

What kind of questions would be asked on a multiple-choice Wisdom Quotient (WQ) Test? - GlowWorm. —Preceding unsigned comment added by 174.130.249.97 (talk) 22:21, 18 July 2009 (UTC)

Wisdom might be a place to start.71.236.26.74 (talk) 02:47, 19 July 2009 (UTC)

Given that the concept of "wisdom" is even more nebulously defined than the concept of "intelligence", and Intelligence Quotient tests are widely regarded as very suspect indicators, I'm not sure what would be gained from such a thing. --98.217.14.211 (talk) 15:48, 19 July 2009 (UTC)