Wikipedia:Reference desk/Archives/Science/2013 March 24

= March 24 =

how oblong could a planet be. could it be shaped like a tic-tac?
I have notice that all planets and moons are round. But they are not perfectly spherical, and I believe some moons are known for being more oblong than others. What is the MOST oblong a planet could theoretically be? what makes a planet oblong?--There goes the internet (talk) 10:52, 24 March 2013 (UTC)
 * I'm not sure about theoretical limits, but you may be interested in the decededly tic-tac-ish Haumea. Fgf10 (talk) 11:00, 24 March 2013 (UTC)
 * There's no place like Haumea. There's no place like Haumea. [tap ruby slippers] Clarityfiend (talk) 11:04, 24 March 2013 (UTC)


 * I think Carl Sagan mentions on Cosmos that when a planet is above a certain mass then gravity pulls it into a spherical type shape. Smaller bodies like asteroids can be much less spherical. Ap-uk (talk) 11:38, 24 March 2013 (UTC)
 * Indeed, see Hydrostatic equilibrium, which I should have linked to in the first place. (I blame sleepy hungover posting.....) Although interestingly our List of Solar System objects in hydrostatic equilibrium says Haumea is actually in hydrostatic equilibrium. Fgf10 (talk) 11:40, 24 March 2013 (UTC)
 * Yes, hydrostatic equilibrium is the right link.However, there is a twist (or a rotation ;-). Rotating bodies in hydrostatic equilibrium will balance gravity and centrifugal force, and so form an oblate spheroid. It can look a bit like a tic-tac from one side, but it's actually more shaped like an M&M. A tic-tac is closer to an prolate spheroid. The most oblate of the 8 currently recognised solar planets is Saturn, where the difference between polar and equatorial diameter is around 10%. --Stephan Schulz (talk) 12:06, 24 March 2013 (UTC)
 * Consider the ellipse formed by the intersection of the surface of a planet (which by definition must be in hydrostatic equilibrium) in the shape of a oblate spheroid, and a plane containing the polar axis. For the planet to be stable in the presence of weak dissipation, the eccentricity of that ellipse can be at most 0.81267.  However, it's also possible for a planet to be in the shape of a tri-axial ellipsoid, like Haumea is.  In that case, the planet can be stable in the presence of weak dissipation when the eccentricity is up to 0.93858.  That eccentricity corresponds to the planet's longest axis being 2.898 times longer than the planet's shortest axis.  That's the theoretical limit, which assumes among other things that the planet has uniform density.  Real planets aren't going to fit the assumptions exactly.  Red Act (talk) 17:47, 24 March 2013 (UTC)
 * Could you explain what "weak dissipation" means in this context? Also, I wonder what the maximum possible difference in gravitational potential energy can be (or more or less synonymously, I think, the maximum possible difference in air pressure assuming the body were granted an average standard atmosphere of pressure) Wnt (talk) 19:55, 24 March 2013 (UTC)
 * If I'm understanding the author of the article I cited correctly, in this context "weak dissipation" means that the planet's mechanical energy can be slowly decreased (turned into heat) due to viscosity, even though the planet is otherwise treated as consisting of an inviscid fluid. Red Act (talk) 20:37, 24 March 2013 (UTC)

Scientific
Is there a scientific reason as to why humans are offended by genitals whereas other mammals are not? For example non-vulgar usernames with genital-related connotations regularly get blocked. Also some of the most vulgar words in English are genital-related. I'd like to know the science behind this. Pass a Method  talk  14:10, 24 March 2013 (UTC)
 * First you need to prove your premise. I don't know of anyone who is "offended by genitals" as such. Types of clothing worn and use of language are matters of culture and climate, not science as such. Suggest you start with Anthropology and branch out from there. ←Baseball Bugs What's up, Doc? carrots→ 15:39, 24 March 2013 (UTC)
 * Why are words such as c*nt, d*ckhead and f*ck considered so offensive? They are all genital-related. There are no such vulgar words related to the hands or ears. Pass a Method   talk  16:51, 24 March 2013 (UTC)
 * The other part of your premise that's false is the notion of animals being "offended", or not "offended". Taking offense to something is strictly a human social construct. ←Baseball Bugs What's up, Doc? carrots→ 21:24, 24 March 2013 (UTC)
 * What of clumsy fingers and cloth ears? As is so eloquently demonstrated by Edmond Rostand, only the weak of wit must rely on such uncreative anatomical vulgarity, when the nose is fodder for insult!
 * Ah no! young blade! That was a trifle short!

You might have said at least a hundred things by varying the tone... like this, suppose,... --Such, my dear sir, is what you might have said, had you of wit or letters the least jot: But, O most lamentable man! - of wit you never had an atom, and of letters, you have three letters only! - they spell Ass!
 * Aggressive: 'Sir, if I had such a nose, I'd amputate it!'
 * Friendly: 'When you sup, it must annoy you, dipping in your cup; You need a drinking-bowl of special shape!'
 * Descriptive: ''Tis a rock! ...a peak! ...a cape! - A cape, forsooth! 'Tis a peninsular!'
 * Curious: 'How serves that oblong capsular? For scissor-sheath? Or pot to hold your ink?'
 * Gracious: 'You love the little birds, I think? I see you've managed with a fond research to find their tiny claws a roomy perch!'
 * Truculent: 'When you smoke your pipe... suppose that the tobacco-smoke spouts from your nose - do not the neighbors, as the fumes rise higher, cry terror struck: "The chimney is afire"?'
 * Considerate: 'Take care, ...your head bowed low by such a weight....lest head o'er heels you go!'
 * Tender: 'Pray get a small umbrella made, lest its bright color in the sun should fade!'
 * Pedantic: 'That beast Aristophanes names Hippocamelelephantoles nust have possessed just such a solid lump of flesh and bone, beneath his forehead's bump!'
 * Cavalier: 'The last fashion, friend, that hook? To hang your hat on? 'Tis a useful crook!'
 * Emphatic: 'No wind, O majestic nose, Can give THEE cold!--save when the mistral blows!'
 * Dramatic: 'When it bleeds, what a Red Sea!'
 * Admiring: 'Sign for a perfumery!'
 * Lyric: 'Is this a conch? ...a Triton you?'
 * Simple: 'When is the monument on view?'
 * Rustic: 'That thing a nose? Marry-come-up! 'Tis a dwarf pumpkin, or a prize turnip!'
 * Military: 'Point against cavalry!'
 * Practical: 'Put it in a lottery! Assuredly 'twould be the biggest prize!'
 * Or... parodying Pyramus' sighs... 'Behold the nose that mars the harmony of its master's phiz! blushing its treachery!'
 * Nimur (talk) 17:17, 24 March 2013 (UTC)


 * As this is a cultural phenomenon rather than a scientific phenomenon, you may get a more accurate response on the Language or Humanities desk. --TammyMoet (talk) 17:24, 24 March 2013 (UTC)

You may find this paper to be of interest. --Guy Macon (talk) 17:40, 24 March 2013 (UTC)

See also here, and watch the documentary in four parts:

part 1,

part 2,

part 3,

part 4.

Count Iblis (talk) 18:26, 24 March 2013 (UTC)

Visual acuity
Is visual acuity an accurate test when measured by opticians? Surely the results would vary depending on lighting conditions in the test room, the brightness of the snellen chart etc. I'm sure eyesight can also fluctuate depending on time of day etc. Clover345 (talk) 17:38, 24 March 2013 (UTC)


 * When I've had those tests done they account for those factors. I am given the test in a windowless room with the lights out, so the only light is that which projects the letters onto the screen.  This light is presumably standardized. StuRat (talk) 21:57, 24 March 2013 (UTC)
 * It's accurate, but it's not precise - see Accuracy and precision. It's a good test of your overall ability to see things, but it can't be used on its own to determine what sort of glasses you need.  Incidentally, the past few tests I've had have used a monitor to display the letters, rather than a traditional paper chart.  Tevildo (talk) 22:07, 24 March 2013 (UTC)

Voyager
When will voyager reach the oort cloud? When it does, how will it avoid getting hit by the rocks there? 64.134.165.238 (talk) 20:49, 24 March 2013 (UTC)


 * See Voyager 1 and Oort cloud. Voyager 1 is travelling at approximately 3.5 AU per year and is currently about 100 AU from the sun, and the Oort cloud starts at approximately 2000 AU from the sun.  It's therefore going to get there in about 550 years.  There isn't really much out there for it to crash into, so "by not being incredibly unlucky" is the answer to the second part of your question. Tevildo (talk) 21:09, 24 March 2013 (UTC)


 * To clarify, there are many objects in the Oort Cloud, but it encloses such a huge volume that the density is extremely low. Being an approximate sphere moves most of the Oort Cloud objects out of the plane of the ecliptic, where most objects in the solar system can be found (and presumably any spaceships flying between those objects). StuRat (talk) 21:59, 24 March 2013 (UTC)
 * So it Oort ought to fly though unimpeded.--Aspro (talk) 23:00, 26 March 2013 (UTC)


 * Also see: http://xkcd.com/1189/ --Guy Macon (talk) 22:02, 24 March 2013 (UTC)

Suckermouth catfish
How do suckermouth catfish take water in to pass over their gills if they use their mouth to form a suction against the aquarium wall? Is water able to be sucked in through the operculum?  DRosenbach  ( Talk 21:19, 24 March 2013 (UTC)
 * Quick search yielded : " Whether the buccal pump system is able to maintain a negative pressure in the oral cavity has since long been a matter of debate. HORA (1930) believed that the lips could not function as a sucker while respiration continued, since the inflowing water would cause the system to fail. ALEXANDER (1965) demonstrated that respiration and suction can function simultaneously, and that both actions continue when the fish is pulled away from the substrate (a vertical aquarium glass). Our results indicate that inflowing water was limited to a thin stream passing under the sucker immediately posterior to each maxillary barbel, a phenomenon also observed by VANDEWALLE et al. (1986) in Hypostomus punctatus." Wnt (talk) 21:22, 24 March 2013 (UTC)

Why do we get toothache?
We can go to the dentist if we have toothache, but animals living in the wild can't. Natural selection must have led to the ability to experience toothache, so what is the advantage of having toothache if you can't do anything about it? Count Iblis (talk) 22:21, 24 March 2013 (UTC)


 * God sends us trials and tribulations that we might become stronger. he also wants bears and fish to become stronger so they can be better animals.--There goes the internet (talk) 22:25, 24 March 2013 (UTC)


 * Perhaps to avoid using that tooth until it falls out, to prevent the infection from spreading ? StuRat (talk) 23:01, 24 March 2013 (UTC)


 * The bodies of plants and animals are subject to many different forms of deterioration. For example, we humans are vulnerable to arthritis, dementia and toothache. Rather than saying natural selection has disposed us to these forms of deterioration, I take the view that natural selection has not yet developed a means of avoiding them. Natural selection is very powerful at fine-tuning plants and animals to survive and reproduce. Apparently these different forms of deterioration do not have a signficant impact on our ability to survive and reproduce. Consequently natural selection is slow at developing a means of avoiding them. Dolphin  ( t ) 23:22, 24 March 2013 (UTC)


 * The etiological factors relating to tooth pain can many. Decay from (largely bacterial) acid accumulation causes tooth structure to demineralize, exposing nerve endings in the dentin to insults such as thermal stimuli, high/low pH, sugar, etc.  Futhermore, gingival pain can be triggered by periodontal inflammation (whether only gingivitis or even periodontitis).  The body deteriorates can evolution cannot be expected to do away with that.  Animals do suffer from both demineralization and gingival disease.  If decay extends into the hollow area within a tooth and directly affects the neurovascular tissue, root canal therapy or tooth extraction is required to alleviate the problem.  Removing plaque/calculus accumulation is required to alleviate gingival inflammation.  That being said, certain animals have diastemata to allow for the free removal of food particles from between teeth.  DRosenbach  ( Talk 23:51, 24 March 2013 (UTC)


 * My wild guess would be that it's the other way around. Evolution brought us pain because it clearly has major advantages to be warned not to use your broken leg. Setting up a system to exempt toothache might have been to costly compared to the advantage (being more productive). Or maybe evolution was just about to invent the feature but dentists entered the just before that. Or maybe in most cases a toothache prevents an animal from using up energy that's needed to heal the tooth. Joepnl (talk) 00:16, 25 March 2013 (UTC)


 * The nerves that supply pain signals with decay/toothache have other purposes. Modern man has a high incidence of decay due to eating modern foods and a long life span, but for early man & animals, the most common reason for tooth pain is/was accidents and fights.  Commonly, the tooth is loosened but not dislodged.  If it is dislodged, most likely the adjacent teeth are only loosened. If the person or animal keeps stress off the tooth as a result of the pain, it will re-knit into the socket and become sound.  Also, if a tooth is lost, it is best not to crunch food into the hole before it heals up.  The nerves also supply nutrients in some way to the tooth.  I've had root canal treatment, which involves removing the nerve.  The result after a few weeks is a dark grey tooth.  I've asked dentists why this happens, and they consistently say they don't realy know, but apparently the nerve is required, as well as the blood vessels, to keep the tooth alive.  Wickwack 58.164.229.78 (talk) 00:44, 25 March 2013 (UTC)


 * Agreed, but there is no way that the nerve can actually supply nutrients, although it may stimulate the tissue. μηδείς (talk) 02:32, 25 March 2013 (UTC)


 * Are you sure? While we tend to think of nerves as only signalling devices, and assume all nutrients come via the blood capillaries, evolution has provided many examples of pressing into service anatomical structures for additional functions:  e.g., brown fat next to the heart supplying nutrients to the heart, conversion of precursors into estrogen by fat, supply of specialised nutrients and signalling chemicals (ege dopamine), required by the processing cells in the brain, by specialised deep brain cells.  Googling "function of nerves in teeth" throws up a lot of professional sites that say things like "the main role of the (pulp) nerves occurs during tooth growth", and "the purpose of the nerve is to make the tooth" as in this site: www.ahendo.com/the-nerve-story.  Frustratingly, I could not find a website that actually sets out what the tooth-making role actually is (consistent perhaps with what dentists have told me - they typically say the nerve is critical to a tooth being live, but just how they don't know.  Wickwack 120.145.50.162 (talk) 03:49, 25 March 2013 (UTC)


 * I think they are just misusing "nerve" to mean "the live part of the tooth". StuRat (talk) 03:54, 25 March 2013 (UTC)


 * Yea, I think the dentist was being a bit sloppy with his language. Most likely he meant that the nerve is intertwined with the blood vessels, so it's impossible to remove the one without damaging the other. StuRat (talk) 03:41, 25 March 2013 (UTC)


 * You could well be right. I once tried to clarify this very point with one dentist, but his reponse to that was along the lines of "well, right now we need to get on with things, so I see other patients on time.  That tooth (indicating the one that was root canalled some time before) is still sound."  Wickwack 120.145.50.162 (talk) 03:56, 25 March 2013 (UTC)


 * Hopefully DRosenbach, our resident dentist, will return to this thread and clarify this matter for us. StuRat (talk) 03:59, 25 March 2013 (UTC)


 * it's interesting that animals react differently than humans to such pain. having had some experience with dogs who have broken their canine teeth, they don't seem to be all that bothered by what would make a human miserable. very often, it seems that animals can be incredibly stoic with regard to pain, but other times they appear just as sensitive as people. of course, i'd imagine it all depends on the evolutionary niche, how other individuals of the species respond to signs of pain, etc. Gzuckier (talk) 02:56, 25 March 2013 (UTC)
 * That could be related to whether there is any point in reacting. Humans also show markedly varying responses to pain.  Small children cry and scream at the most minor scrape, because they know it gains them a hug and tender words from Mum.  I saw recently a 5 year old fall off her bike and take some skin off.  She looked about, I assume to see if Mum or Dad was around, then got back on her bike and carried on. I have a faulty hip joint.  When it first hurt, about 15 years ago, I thought it was terrible, and rushed off to the doctor.  His response after viewing a CAT-scan was essentially "You'll just have to put up with it.  Eventually we'll give you an artificial joint, but not now, as artifical joints have a limitted life and have significant limitations."  Well, it still hurts.  But I just put up with it - pretty much ignore the pain.  I've got used to it and it now doesn't seem anywhere near as bad as I first thought.  When a dog breaks a tooth, he is unaware that humans can stop the pain.  No point worrying about things you can't change.  Wickwack 120.145.50.162 (talk) 04:15, 25 March 2013 (UTC)

Tree identification
Can anyone help with this? It was taken today in southern California.  DRosenbach  ( Talk 23:46, 24 March 2013 (UTC)
 * I don't know if anyone here will be able to answer it, but if they can't, you might try taking it to WikiProject Plants or another WikiProject listed at WikiProject Tree of Life. Ryan Vesey 00:00, 25 March 2013 (UTC)
 * Hard to tell from this picture. Could be a dogwood.  -- Jayron  32  00:18, 25 March 2013 (UTC)
 * The flowers look a little complex to be a dogwood, but it's very difficult to make out anything. μηδείς (talk) 01:23, 25 March 2013 (UTC)
 * Oval leaves, smooth bark, slight curve and criss-crossing of some secondary branches, grouping of flowers, I'm thinking prunus genus, in which there are unfortunately many species, but hopefully it's a start. Richard Avery (talk) 08:09, 25 March 2013 (UTC)
 * I was thinking prunus (plum, almond, etc.) as well, largely because there are lots of them blooming at this time of year in various parts of California. Looie496 (talk) 20:06, 25 March 2013 (UTC)


 * These links may be helpful.
 * Ask an Arborist here - Tree World
 * Ask an arborist
 * ask-an-arborist.com
 * Tree Care Answers from Ask An Arborist
 * Untitled Document ("Do you have a tree care question? Ask the arborist!")
 * Ask Arborist
 * —Wavelength (talk) 20:21, 25 March 2013 (UTC)