Wikipedia:Reference desk/Archives/Science/2010 June 1

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June 1

Center of mass question

Suppose two particles, far from any other influence, are orbiting around their center of mass due to gravitation. Then, imagine that a third object is introduced to the system. This third object will obviously will move the center of mass. Will the two objects still move about the center of mass in the same way? If so, is this a general rule about center of masses? 173.179.59.66 (talk) 00:19, 1 June 2010 (UTC)

It is really complicated. See Three-body problem. With two particles, they will both orbit in ellipses around the centre of mass. With three particles, they can do all sorts of crazy things. --Tango (talk) 00:26, 1 June 2010 (UTC)

All right, I didn't expect it to be that simple, thanks. 173.179.59.66 (talk) 00:56, 1 June 2010 (UTC)

Generally in real systems you'll only have two bodies orbiting as a very-close-to-true two-body system, with the third body orbiting around the two bodies' center of mass from a much-farther distance. However, in our Solar System, small things like comets and other [[Kuiper belt] objects sometimes get disturbed just enough by the larger planets to be ejected into the central solar system, giving us the weird new comets we see on occasion (or the one that crashes into Jupiter). - User:SamuelRiv 1 June 2010

Sure, if the third body is small enough and far away enough not to significantly affect the other two bodies and is far enough away that the other two bodies essentially merge into one body, then you can get an approximate solution by doing the two-body problem twice. It would only be approximate, though. Exact solutions to the 3-body problem are only known for a few very specific (an unlikely to occur in real life) situations. --Tango (talk) 15:41, 1 June 2010 (UTC)

Tango - in an isolated 3-body system, as in a trinary (I don't use tertiary) star, these systems of a close pair with a far-away orbiter (no matter how massive they are) are the only ones observed. Of course the precise calculation is notoriously unsolvable, and in the case of a many-body solar system, it is utterly a mess with small-bodies being quite unpredictable. SamuelRiv (talk) 16:10, 2 June 2010 (UTC)

I wasn't aware they were the only ones observed, but it doesn't surprise me - more complicated 3-body systems tend to be unstable, so one of the three stars would probably break away from the other two sooner or later. If the far-away orbiter is sufficiently massive (which I think is unusual) then it will have a significant impact on the way the other two stars orbit each other. --Tango (talk) 16:14, 2 June 2010 (UTC)

That's not exacly right. Globular clusters do not fit within that cathegory. Dauto (talk) 20:40, 3 June 2010 (UTC)

Methanol in water

When something like methanol goes into aqueous solution, the hydrogen on the edges of the methanol form weak polar hydrogen bonds with the negative side of the surrounding water, thus the methanol goes into solution. But, why doesn't the oxygen in the middle of the methanol form some sort of similar bond with the positive, hydrogen side of other water molecules? It seems that if the outside of the methanol has a little bit of a positive charge, the middle might have the reverse. --The High Fin Sperm Whale 03:45, 1 June 2010 (UTC)

You are right! The Oxygen is a hydrogen bond acceptor. Have a look in the hydrogen bond article.--Stone (talk) 05:13, 1 June 2010 (UTC)

Sodium acetate heating pads

I have some of these pads, and one of them seems to recrystallise on its own, very slowly, without any stimulus. Its subsequent heating activity is, of course, impaired. Should I dispose of it, and if so, what is the safest way? Could I, for example, just put it into a rubbish bin? --TammyMoet (talk) 09:04, 1 June 2010 (UTC)

I hope this doesn't cross the line to legal advice, but as far as I understand, there is nothing toxic or otherwise particularly harmful in them. (Of course, you will make sure to separate the metal for recycling, identify the type of plastic used in the shell and sort it accordingly, water your flowers with the liquid and use the acetate to season some crisps...)--Rallette (talk) 09:58, 1 June 2010 (UTC)

Sodium acetate is not toxic in normal quantities; react it with acids and you get vinegar. There is probably a scratch in the bag that allows the unstable supersaturated solution to condense as crystals. You can dilute the sodium acetate with water and wash down the drain; shouldn't hurt any more than vinegar. --Chemicalinterest (talk) 11:09, 1 June 2010 (UTC)

Thanks for your help guys - you're really fast!--TammyMoet (talk) 13:20, 1 June 2010 (UTC)

The Relative Passage of Time

It is a common anecdote that the days seem to move faster as an adult than when you were a teenager and certainly faster than when you were a child. Does this phenomenon continue to accelerate during adulthood? That is to say does someone in their 40s experience time (on average) to be faster than someone in their 20s? TheFutureAwaits (talk) 11:00, 1 June 2010 (UTC)

I think it has to do with the "busyness" of your days. As a child one doesn't have many responsibilities and cares like adults do, so time seems to move slower for them. Time also seems to move faster when you are more busy. --Chemicalinterest (talk) 11:11, 1 June 2010 (UTC)

Yes, I'm sure that is a factor, but the effect of time speeding up seems to continue into retirement and even to accelerate, even when days are less busy. Dbfirs 13:23, 1 June 2010 (UTC)

And I'm a complete waster, with absolutely nothing to do all day, and still find that now, in my 30s, the years seem to fly by - unlike when I was, say, seven, and it seemed an eternity until I would be eight. One possibility is that things seem to last longer when they surprise you, and that children are permanently surprised. (It would be funny if it turned out to be physiological, to do with brain chemistry. There are drugs which alter the perception of time, so it's not impossible.) 213.122.61.131 (talk) 20:21, 1 June 2010 (UTC)

Think of it this way: when you are one day old the next day is one half of your whole life at that point, when you are 20 years that same day is 1/7304th of your whole life at that point. —Preceding unsigned comment added by 165.212.189.187 (talk) 13:26, 1 June 2010 (UTC)

Simvastatin toxicity

Is sequestered bile acids beyond what the body can tolerate to lower cholesterol levels the mechanism of Simvastatin toxicity in doses above 160mg? 71.100.8.229 (talk) 11:34, 1 June 2010 (UTC)

Simvastatin is one of the statin drugs that inhibit the enzyme HMG-CoA reductase that is part of the endogenous cholesterol biosynthesis pathway. Statin drugs do not sequester the bile, there are a separate class of cholesterol reducing agents that act through sequestration. There are several different types of toxicity that can occur with simvastatin. Can you specify what you mean? --- Medical geneticist (talk) 12:08, 1 June 2010 (UTC)

I can't seem to find more than the maximum dose as 80mg or the toxic dose as 160mg if that helps. I'm interested in all types of toxicity for Simvastatin from excess dose to interaction with other drugs or interaction of the implied conditions taking Simvastatin represents. For instance, high cholesterol is an indicated condition that suggests that medications which restrict blood vessels such as medications which dilate pupils are toxic in combination with the implications of taking Simvastatin, i.e. high cholesterol. 71.100.8.229 (talk) 13:10, 1 June 2010 (UTC)

Huge sinkholes in Guatemala

There are reports in the new about a gigantic sinkhole in Guatemala ([1]). A web search turns up stories about another occurrence in 2007 ([2]). How were these sinkholes created? Why do they look almost perfectly cylindrical? Where did the earth that originally occupy the hole go? —Preceding unsigned comment added by 173.49.15.136 (talk) 12:00, 1 June 2010 (UTC)

It starts with a system of caves, and an underground river. The river falls down a small hole, over time it enlarges the hole, the swirling motion as it does so tends to make the hole round. See Kettle hole, Plunge pool, and Pothole#Other_uses. Like this photo, sometimes they call them "Glory holes". Eventually there was a massive, and deep hole in there, covered by an earth "roof". Probably fed at the side, with a deep drain. The soil was all washed away by the river, as over time the land above falls down into the water. During that massive rain storm, probably the river level went up a lot, and washed even more soil. To the point that it could not support it's own weight, and fell in. If you look closely at the photo you'll see it's full of water at the bottom. Ariel. (talk) 12:37, 1 June 2010 (UTC)

So close to the meteor impact of 65 million years ago. How far down and how thick is the iridium layer in the hole? 71.100.8.229 (talk) 13:51, 1 June 2010 (UTC)

There might be little or no iridium layer actually at ground zero itself, as the huge explosion caused by the vaporisation of both the meteorite and the rock it struck would have blown all the meteoritic material (which contained the iridium in excess of usual terrestrial concentrations) high into the atmosphere, dispersing it around the globe. Although a small proportion of this material would have resettled at the immediate impact point, that immediate area would have been so heated and/or disturbed by the impact that it would have probably remained in state of turmoil (doubtless there's a technical word for this) long enough to mix up the fallout and prevent the formation of the obvious K-T boundary layer found elsewhere.

In the wider area of the Chicxulub crater, around whose boundaries formed the ring of cenotes/sinkholes that were the clue leading to the feature's discovery, the article's Geology and morphology section states "The K–T boundary inside the feature is depressed between 600 and 1,100 m (2,000–3,600 ft) compared to the normal depth of about 500 m (1,600 ft) depth 5 km (3 mi) away from the impact feature." The original paper from which these data are taken, Hildebrand, Penfield et al 1991 4, might also give the layer's thickness. (87.81.230.195 (talk) 23:34, 1 June 2010 (UTC)

I would be careful with the term "glory hole", it has other meanings - Q Chris (talk) 15:21, 1 June 2010 (UTC)

Crayfish

Any crayfish experts here? - this question Wikipedia:Reference_desk/Miscellaneous#Fastest_Animal slipped through the net (excuse the pun).87.102.77.88 (talk) 13:16, 1 June 2010 (UTC)

The responses on the Miscellaneous page seemed to hit the nail on the head. Do you have a particular clarification you'd like? I will just emphasize two points: First, that the consensus seems that crayfish aren't fast in terms of velocity, but rather acceleration (0-60 in 3 seconds, to use a car term). It would be neat if we had a page on the fastest-accelerating animal, because surely none of those listed in Fastest animal would qualify.

Second, the key to this rapid response is a very conductive "wire" that can connect any kind of stimulus to the tail muscles almost instantly. Human reaction time in such a situation is at best 160ms, which for a crayfish would make them easy prey (finding a list of animal reaction times is very difficult, if someone might help). The essential problem is that the "wire" is a neuron, which is not a very good conductor. Mammals get myelin, a fatty insulation, around some neurons to make signals go faster, but arthropods have to instead make their response neuron thicker. At the end of the day, the sequence is that a stimulus from the eyes or wherever travels to the brain and then shoots down this giant neuron into the tail causing this very fast reaction kick. Sorry I can't be more specific. SamuelRiv (talk) 16:39, 2 June 2010 (UTC)

tendinosis or tendonitis?

Hi all. Are tennis and golfer's elbow examples of conditions caused by tendinosis or tendonitis? The articles on these conditions do not say. Presumably tennis elbow is a tendinosis as there is no inflammation involved and golfer's is a tendonitis because there is histological inflammation? If my presumptions are correct then the link to tennis elbow on the article on tendonitis should perhaps be removed? RichYPE (talk) 13:25, 1 June 2010 (UTC)

"-itis" means "inflammation", and "-osis" means "condition" (usually not a good one). Both golfer's elbow and tennis elbow are associated with inflammation. --Sean 16:26, 1 June 2010 (UTC)

I had heard that tennis elbow was not associated with inflammation, and the wiki article on this seems to say the same thing. 'The condition is also known as lateral epicondylitis ("inflammation of the outside elbow bone"), a misnomer as histologic studies have shown no inflammatory process.' RichYPE (talk) 16:05, 2 June 2010 (UTC)

The article goes on to say that there is inflammation, so I don't know what to think and will defer to someone with more expertise than myself. --Sean 18:23, 2 June 2010 (UTC)

Just by the way, it's spelled tendinitis; there's no o in the word. I assume this has something to do with the Latin (e.g. the Italian word for "tendon" is tendine). --Trovatore (talk) 04:52, 3 June 2010 (UTC)

What's a "Twin Cylinder Reversible Turbine"?

Looking at this 1913 patent, I'm confused: what is it supposed to do? It's obviously some sort of steam turbine; am I correct in guessing that it works inside a steam engine to make the engine more efficient? Nyttend (talk) 15:16, 1 June 2010 (UTC)

If I understand correctly (and I may not be), it is a steam turbine that can be put into reverse (i.e. it spins the opposite direction). Falconus^{p t c} 18:11, 1 June 2010 (UTC)

I wonder if 'cylinder' refers to piston and it is a turbine engine with a piston based gas generator eg Free-piston_engine#Gas_generators , not sure how that would be reversible.

It may not even be an engine - some variation on the fluid coupling seems possible.

Also could reversible mean 'reversing' rather than reversible as in thermodynamics?

(sorry I'm guessing) Is there a better link - all I saw was a very brief abstract - I'm not even sure it is steam from the info I've got. It's US Patent 1064824 - maybe someone else has better resources. 87.102.77.88 (talk) 18:40, 1 June 2010 (UTC)

Silly me here it is http://www.freepatentsonline.com/1064824.pdf

It was reversible as in 'can be put in reverse gear'. As far as I can tell it's a stand alone turbine as described.? In fact the patentee describes one of it's advantages as being compact and able to go in the base of a ship - so there probably wasn't any conventional steam engine involved.

Note - the engine seems to rely on gas flow, and there appears to be no expansion (didn't read it all) - this would have been a tremendously inneficient engine - one of the later patents that references this one corrects this flaw. ie this 87.102.77.88 (talk) 19:00, 1 June 2010 (UTC)

No wonder the inventor kept his day job; he was a prominent smalltown physician. I discovered this patent while researching to write an article about his house. Thanks for the input! Nyttend (talk) 21:49, 1 June 2010 (UTC)

force

what are active and passive forces? —Preceding unsigned comment added by 122.167.120.52 (talk) 15:33, 1 June 2010 (UTC)

A Google search for "active and passive force" results in these definitions from the University of Vermont College of Medicine (2000). Hope this helps, [sd] 16:19, 1 June 2010 (UTC)

I think the term passive force refers to something like friction or viscous force, which only exist as resistance to motion. Say I apply a pushing force of 500 N to a heavy box, but the friction prevents the box from moving. We know that the friction is equal to 500 N, since the box shows no acceleration. However, if I stop pushing, there won't be a 500 N of friction to cause the box to accelerate towards me. I think it is in that sense that the force is passive. --173.49.15.136 (talk) 12:33, 2 June 2010 (UTC)

Sima Martel and Sima Humboldt

Is the sunlight reach the bottom of it? And will animals survive if it drop into it? Is there any possibility there's ancient animals or plants live in it? roscoe_x (talk) 18:39, 1 June 2010 (UTC)

According to our (brief) articles about these holes, (Sima Martel and Sima Humboldt) they are both about 300 meters wide and about 300 meters deep. They aren't narrow holes at all. That means that the sun would only have to be about 45 degrees up above the horizon to light at least a portion of the floor. Google Maps says that they are at about 4 degrees of latitude above the equator - so there will be days in the summer when the sun shines vertically down into the holes, illuminating almost the entire floor of the sink-holes - except that the floor of the holes are slightly wider than the top - so there are probably some small regions that don't get sunlight. However, it's obviously quite light down there most of the time.

Given that, it would be very surprising if there were no plants down there - you'd expect seeds and fruits and nuts to fall down there all the time, so it's quite likely that the floor is mostly covered with the same kind of vegetation as the surface. Animals are a bit more problematic. It's hard to imagine very large animals getting down there and surviving long enough to breed in such a limited space...but anything that can climb a rock wall could make a living there - as could very small animals. With a constant influx of modern life raining down into the holes, it's hard to imagine 'ancient' things living down there. Having said that, many caves have unique life forms (typically, blind, white things) that evolved from animals that fell into the cave system somehow...it's not impossible that such things are in the darker corners. SteveBaker (talk) 00:40, 2 June 2010 (UTC)

Mafeking Oil - obsolete veterinary preparation

Just watching All Creatures Great and Small, and mention was made of a preparation called "Mafeking Oil". It was being used by a farmer as a muscle rub on a lame cow, and the cow had licked the oil off her leg and developed vesicles in her mouth. Siegfried duly castigated the farmer for using such an out-dated and dangerous treatment, and said that "the only good thing the Germans did in the war was to bomb the factory that makes it". So - it was some sort of embrocation, unavailable after the Second World War, and acidic. Anyone know what it was? I have googled, and found nothing (except another person asking the same question). DuncanHill (talk) 18:58, 1 June 2010 (UTC)

Hmm. Dippel's Oil is an unpleasant oil once used with livestock, though since it's supposed to repel animals I doubt the cow would have licked it off. I feel like I've heard of Mafeking oil before, too, but then I also find Shatner's bassoon to be plausibly part of the brain, so perhaps what we have here is just an example of James Herriot being a good writer.213.122.61.131 (talk) 21:02, 1 June 2010 (UTC)

According to a Google Books search, the book All Creatures Great and Small doesn't mention that -- it mentions castor oil, linseed oil, and cod liver oil, but no Mafeking oil. In fact no book of any sort is found that mentions that. Also no mention of mouth vesicles in any of his books. Looie496 (talk) 21:58, 1 June 2010 (UTC)

The vesicles were initially suspected to be foot-and-mouth disease, which I'm sure he does mention. DuncanHill (talk) 22:15, 1 June 2010 (UTC)

Have you considered artistic license? Mafeking being a suitable name for a potent medicine (ie from Siege of Mafeking) - possibly the hypothetical (and possibly imaginary) bottle had a military scene on ala Camp Coffee but with a greater suggestion of physical activity and free from any suggestion of lameness. Maybe simply the words 'mafeking' where enough in themselves. 87.102.77.88 (talk) 23:46, 1 June 2010 (UTC)

The potion referred to is indeed mentioned in televisionseries All Creatures Great & Small Season 4 episode 7 - Ace, King, Queen, Jack. It cannot be found on google, which doesn't mean it never existed. Maybe asking around at Thirsk area ( where Alf White aka James Herriot lived ) would shed some light, asking the oldest farmers around. They should still know it.

Eeee by gum, that be "Ma fuc*ing oil". Special invenshun of Alf Wright.220.244.245.42 (talk) 03:48, 15 January 2015 (UTC)

Not Sure what it's original purpose was, but it came from Mafeking South Africa. It was the oil used to make Shaka [The Zulu Chief] look young in the movie Shaka Zulu. Which it did by darkening his hair. I believe it was originally used as a heavy preserving oil to keep metal parts from rusting in wet areas. Essentially, like hiding the grey by putting motor oil in your hair. — Preceding unsigned comment added by 101.98.47.42 (talk) 08:37, 5 May 2018 (UTC)

Live bacteria in food

I know I sorta asked this question, but what other foods besides those containing dairy has live bacteria in it? The reason I ask is that I am extremely lactose intolerant and eating yogurt will not be beneficial to me. Nor would drinking beer. Just wondering. Thanks! Reticuli88 (talk) 19:17, 1 June 2010 (UTC)

Just about any food will have some non-zero number of live bacteria on it unless you just pulled it out of an autoclave. You breathe in a huge number of bacteria a day, and some of those bacteria land on your food. Is there a specific species of bacteria you are looking for in food? Googlemeister (talk) 19:21, 1 June 2010 (UTC)

I guess the same ones that are present in yogurt. The "good" bacteria. Reticuli88 (talk) 19:23, 1 June 2010 (UTC)

I know I've already given this answer but see Category:Fermented foods - most are not pasteurised - and so will still contain live bacteria. Clearly many are regional and you won't be able to get them whereever you are. I would guess Fermented soy products , Fermented bean paste , Fermented bean curd and Fermented fish are likely candidates, another is Sauerkraut

This [3] mentions some common products - miso is probably gettable in many places. 87.102.77.88 (talk) 19:41, 1 June 2010 (UTC)

For a list see the section just above Probiotic#Multi-probiotic 87.102.77.88 (talk) 19:45, 1 June 2010 (UTC)

Tempeh is a nice product. I enjoy it. Not sure if it provides what is called for. But it is a fermented soybean product. Bus stop (talk) 19:52, 1 June 2010 (UTC)

Just to state the obvious, remember if you want live bacteria, you can't cook your source or heat it much above 37 degrees celsius. Also based on our yoghurt article, have you looked for lactose free yoghurt? It evidentally exists in the UK Lactofree, seems likely it may exist in the US as well. And it seems soya yoghurt also exists. I presume some of these contain live cultures. Nil Einne (talk) 21:07, 1 June 2010 (UTC)

It is also possible to buy capsules containing such bacteria in health-food stores. I am neither recommending nor dis-recommending these; just letting you know they exist. --Trovatore (talk) 20:06, 1 June 2010 (UTC)

Kombucha contains loads of bacteria. Looie496 (talk) 22:01, 1 June 2010 (UTC)

I don't believe the health of your gut flora relies on regular consumption of live bacteria, contrary to what the advertisers of Yakult would want you to believe. Vespine (talk) 05:53, 2 June 2010 (UTC)

And, of course, contrary to what our articles Gut_flora#Alterations_in_balance and probiotics say. That not everyone will benefit from it is pretty clear: that many people in many different circumstances will benefit from it is supported by the evidence. The problem lies in the advertising suggesting that everyone needs it all the time: but then, there are plenty of adverts that talk about specific symptoms being relieved by probiotics. 86.164.69.239 (talk) 19:01, 2 June 2010 (UTC)

Gull wings

Does a gull wing or inverted gull wing cause more drag than a straight wing? Also, does it provide more or less lift? Thanks, --The High Fin Sperm Whale 19:36, 1 June 2010 (UTC)

I can't answer your question, but see anhedral and dihedral (aircraft). As a pilot, the difference that I have been interested in, is what they do for stability. Falconus^{p t c} 21:08, 1 June 2010 (UTC)

So what does it do to stability? --The High Fin Sperm Whale 21:29, 1 June 2010 (UTC)

RTFA? --Tagishsimon (talk) 21:47, 1 June 2010 (UTC)

I have no idea what "RTFA" means, but a dihedral makes an airplane more stable, and an anhedral makes it less stable. They sometimes put anhedrals on designs where the plane is too stable (you do need to be able to turn them, after all). The plane I fly (PA28) has a very distinct dihedral, making it very stable, which is what you want if you aren't planning on doing stunts. Falconus^{p t c} 22:43, 1 June 2010 (UTC)

I think there's a basic problem with answering your question - more or less under what conditions? for the same width, breadth, weight etc?87.102.77.88 (talk) 22:03, 1 June 2010 (UTC)

What I'm asking is, if you have have a straight wing and a gull wing of the same length, width, etc., what differences will it make to stability, speed, lift, drag, etc. And what does 'RTFA' mean? --The High Fin Sperm Whale 22:14, 1 June 2010 (UTC)

RTFA means that an answer to your "what does it do to stability" question was to be found by reading the articles linked to in the response above it. --Tagishsimon (talk) 22:52, 1 June 2010 (UTC)

And the 'F' should just be left to my imagination? Falconus^{p t c} 23:04, 1 June 2010 (UTC)

Flying. I'm sure it's flying... --Tagishsimon (talk) 23:11, 1 June 2010 (UTC)

We have an article, of course: RTFA. (Well, it's a redirect to an article in which "RTFA" is mentioned.) Comet Tuttle (talk) 23:56, 1 June 2010 (UTC)

At a basic level lift depends on the angle of attack - no difference as a first approximation.

Drag will depend primarily on the thickness of the wing - here again - no difference as a first approximation for wings of the same thickness.

Speed will be a function of drag - assuming the wings have the same sweep - no difference.

Stability - not sure here - but a gull wing has two angles for anhedral/dihedral , whereas a 'normal' wing has one and you haven't specified what it will be - so I don't think that is answerable yet. Ignoring that aspect for a moment -stability depends on the whole aircraft - ie the other smaller wings etc .. so impossible to say.

There should be an article comparison of different wing designs, benefits and drawbacks (Wing configuration is solid but doesn't answer it)- but I'm not familiar with the aviation area of this wiki - maybe someone else can point at a coverall article?87.102.77.88 (talk) 23:28, 1 June 2010 (UTC)

Actually if you read the article Gull wing from top to bottom I think you'll get the impression that the main reason for having a gull wing is to solve secondary (non flight) engineering problems (or issues with centre of mass) rather than any intrinsic pluses or minuses flight wise.. 87.102.77.88 (talk) 00:10, 2 June 2010 (UTC)

The gull wing and inverted gull wing have no effect on lift and drag, but they do provide the designer with the perfect opportunity to ensure adequate clearance between the propeller(s) and the ground; and to allow short undercarriage legs. Dolphin (t) 23:15, 2 June 2010 (UTC)

There is much more to the calculation of drag than implied here. The gull wing will certainly create some sort of vortex drag at its sharp bend - such drag appears also at the wingtips of aircraft, which is why some have the "winglets" at the tips. It will be negligible for low-speed gliders, but likely quite important for any modern powered aircraft. Unfortunately, I don't have the expertise or resources to answer in-depth. Why a gull will glide with such a wing configuration is also unknown to me, but consider looking up a nice computational model of bird flight. SamuelRiv (talk) 02:26, 3 June 2010 (UTC)

Stukas

The article on the Stuka (in the specs section) says it has two forward MG 17 machine guns. Are these the removable pods mounted on the wings (such as the picture left) or are these internal and non removable? And when these machine gun pods are mounted, can the two 110 bombs still be mounted on the wings? --The High Fin Sperm Whale 20:20, 1 June 2010 (UTC)

The article on the Stuka says The offensive armament was two 7.92 mm (.312 in) MG 17 machine guns fitted in each wing, operated by a mechanical pneumatics system from the pilot's control column. original research but I would not think it would interfere with the bomb load. MilborneOne (talk) 20:26, 1 June 2010 (UTC)

The plane in that picture has some enormous guns! Are those really MG 17s? Here's a cross section of a Ju87(b) with guns internal to the wing: [4] ... this was normal. 213.122.61.131 (talk) 20:43, 1 June 2010 (UTC)

If you read the Junkers Ju 87#Ju 87G section, it's immediately clear that your picture shows a variant used for anti-tank warfare on the Eastern Front. Not many were ever produced, I guess. The large guns are evidently 37 mm Flak 18 cannons. The article also says that they were designed to carry one 1000 kg bomb. Buddy431 (talk) 20:50, 1 June 2010 (UTC)

Or maybe BK 37 cannons based on the earlier Flak 18 cannons (and superseded by the 3.7 cm FlaK 43? Those articles need to make clearer the relationship between the different guns). Buddy431 (talk) 20:56, 1 June 2010 (UTC)

(ec) The photo caption notes that the gun pods are 37mm cannon, probably for an anti-vehicle/anti-tank role. They appear to be fixed to the hard points that would otherwise mount the 50kg bombs. — Lomn 20:51, 1 June 2010 (UTC)

Sinkhole

In Guatamala, where did the contents of what is now a sinkhole go? It's not like the Earth is a hollow ball and it fell into the center, right? DRosenbach ^{(Talk | Contribs)} 22:19, 1 June 2010 (UTC)

Dissolved away over many hundreds/thousands of years like other features where the bedrock is limestone. There was probably a limestone cave beneath the sinkhole whose roof collapsed suddenly, the space had already been created. Mikenorton (talk) 22:35, 1 June 2010 (UTC)

(edit conflict..modified) - for this reason sinkholes are often connected to cave systems and underground rivers Subterranean river

For the final collapse see the second to last paragraph in Sinkhole. 87.102.77.88 (talk) 22:38, 1 June 2010 (UTC)

There's a nice diagram of tooth decay limestone cave formation here [5] (scroll down).87.102.77.88 (talk) 22:40, 1 June 2010 (UTC)

See also Wikipedia:Reference desk/Science#Huge sinkholes in Guatemala, above. --Tagishsimon (talk) 22:36, 1 June 2010 (UTC)

See also sinkhole and cenote. Cacycle (talk) 22:38, 2 June 2010 (UTC)