Wikipedia:Reference desk/Archives/Science/2012 February 4

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February 4

Pterodactyl

Would a pterodactyl be strong enough for a person to be able to ride on its back? --108.225.115.211 (talk) 00:31, 4 February 2012 (UTC)

Wouldn't you be hit by flapping wings there ? StuRat (talk) 00:33, 4 February 2012 (UTC)

Very doubtful. What would be the point of having that extra strength? The extra muscle mass would mean they need to eat more, which would decrease their chance of survival. Evolutionary pressure is very strongly towards flying creatures being as light as possible and no stronger than they need to be to get off the ground (and perhaps to pick up prey, but according to pterodactylus only had a wingspan of 1.5m, so they weren't large enough to eat human-sized prey). --Tango (talk) 00:41, 4 February 2012 (UTC)

Pterosaurs in general grow to be much larger, up to a 10m wingspan (see Pterosaur size). They seem to have a lot of tricks that help keep them aloft at that size, including internal air sacs to reduce their density as much as possible. The article of one of the largest pterosaurs, Quetzalcoatlus, talks about their weight (70-200 kg), them needing to vault themselves to get airborne, and includes an illustration of them doing their feeding on the ground. Most of the mighty predatory birds that need to do some impressive lifting feats (like the mighty eagles dropping goats off of cliffs) start lifting mid-flight, having a lot of momentum built up to work with, but is not sustainable flight - they lose altitude continuously.

To answer your question, at the high-end estimated weight of a Quetzalcoatlus, it may have more room to spare in terms of carrying capacity than one would think, but a 200kg flyer could certainly never haul a 100kg person with any lift. I can't give a calculated estimate without years of incredible engineering research as these scientists have employed, but I can tell you immediately that each downbeat of the wings has to be at least 25% more powerful than normal and 50% more frequent. That's like me jogging to the grocery at a comfortable 8-minute mile, but then having to carry food back at an impossible 4:30. SamuelRiv (talk) 01:22, 4 February 2012 (UTC)

Scale comparison for a human and Quetzalcoatlus, an azhdarchid.

(e/c) No. The largest pterodactyls (suborder Pterodactyloidea) are the members of the family Azhdarchidae, the azhdarchids. Azhdarchid flight is relatively poorly known, but like SamuelRiv said, they are believed to engage only in limited anaerobic (flapping) flight, and be predominantly soaring/flap-gliding animals that utilized columns of rising air to keep aloft. They launched by a running/flapping start and the addition of half to a third (a human's weight) of their current estimated body weight (~200 kg (440 lb) for an azhdarchid with a wingspan of 10 to 11 m (33 to 36 ft)) would make that quite impossible. Not to mention the aerodynamic drag and balance problems produced by a human rider. Azhdarchids are also believed to be stalkers, hunting their prey on foot like modern storks, not skimmers like some of the more commonly known marine pterosaurs (e.g. Pteranodon). They can not pick up prey while in flight because of the drag produced. A human riding them would produce similar if not even more catastrophic drag.-- OBSIDIAN†SOUL 01:43, 4 February 2012 (UTC)

But according the article, many of those claims of large-animal flight, consistent with today's birds, are under dispute for pterosaurs. Surprisingly to me, there are apparently models for flight that is athletic and dynamic like a swallow, not soaring like an owl. As an analogy this might be improper, but one might consider in human flight, the size and shape of a plane varies greatly with what it has to carry - in no sense can one make a plane "scale up". So to make a small one-person recreational airplane carry 20 people, you can't simply make the wingspan 20 times bigger and/or the engine 20 times stronger - you have to redesign it. SamuelRiv (talk) 18:45, 4 February 2012 (UTC)

Swallows are dynamic soarers actually. They do not engage in much anaerobic flapping. While azhdarchids are more likely to be such, given their shape and the velocities they can achieve, and not like the heavy poor flyers of today (like pelicans); also consider the fact that the faster they fly, the greater the effect of parasite drag. An extraneous human clinging on its back would produce such a drag. The paper points out the inappropriateness of the comparison with birds. The shape, lack of feathers, bend location, muscle structure, wing membrane (with matted pycnofibers that give it additional structural integrity) and bone strength of azhdarchids are too different from birds for any accurate comparisons. Thus the older estimates of azhdarchids only having an estimated weight of 80 kg (180 lb) for an individual with a 36 m (118 ft) wingspan used for the flying model is now considered wrong. But that argument is really only useful in refuting the assertions that azhdarchids were flightless. 70 to 100 kg (150 to 220 lb) human is still a third to half of the largest pterosaur's weight. Unless they had propellers, they wouldn't even be able to launch, much less keep aloft.-- OBSIDIAN†SOUL 01:34, 5 February 2012 (UTC)

Cycloaddition Mechanism

Hello. What is the reaction mechanism for the addition of dichlorocarbene to cyclohexene? Cited sources are appreciated. Thanks in advance. --Mayfare (talk) 06:35, 4 February 2012 (UTC)

We have an article about dichlorocarbene, with a section entitled "Reactions" that tells you the product but not the mechanism. But it also suggests that the "dichloro" and the "cyclohex" details might not be important (they are not altered by the change taking place in the given reaction). So take a look at the more generic carbene article and maybe in particular the "Reactivity" section. DMacks (talk) 15:18, 4 February 2012 (UTC)

Most numerous vertebrate species

I recently heard a naturalist claim that humans are the most numerous vertebrate species. Is this true? If so, which other vertebrate species have populations in the billions? I would have thought that the brown rat and some domesticated animals would challenge humans for numbers. Warofdreams talk 13:47, 4 February 2012 (UTC)

That definitely sounds wrong. Biomass (ecology)#Global biomass says there are more chickens. Chicken says it is the most common bird. I guess there are other more common vertebrates. PrimeHunter (talk) 14:23, 4 February 2012 (UTC)

I don't think anyone really knows. He's wrong, but probably not by much, we'd probably be in the top 50 or something, few species are really readily adaptable to a wide range of ecological conditions like humans are. And to be fair, the most likely candidates (domestic and synanthropic animals) only attained their population sizes and distribution because of humans. On the opposite end of the spectrum, passenger pigeons which was believed to have once reached an estimated population of 3 to 5 billion were singlehandedly decimated to extinction within a century by humans.-- OBSIDIAN†SOUL 14:34, 4 February 2012 (UTC)

The brown rat article claims there are 1.3 rats in the UK per person (which, if it's true, would obviously push the rats ahead of the humans). But it cites an hysterical piece in, of all sources, The Sun, which takes its info from Rentokil (Britain's largest ratcatcher, in whose interests it surely is to embiggen the "rat threat"). Snopes cites rather better sources for New York City claiming a ratio of only 1:36. -- Finlay McWalterჷTalk 15:00, 4 February 2012 (UTC)

Rodents aren't limited to cities, they also do quite well in farm fields. In the U.S., we have around 220 million acres just under corn, soybeans, and wheat, and, even at a conservative estimate of 40 rodents/acre, U.S. grain field rodents are more populous than humans. (They also love fruit orchards and grass, e.g. alfalfa fields.) However, most of them are not brown rats, they are meadow voles.--Itinerant1 (talk) 19:56, 4 February 2012 (UTC)

Rodentia, however, is not a single species. Few rodent species are truly cosmopolitan, and the ones that are are synanthropic species that stay close to human habitations. Field mice in Pakistan, for example, will be most likely to be a different species than field mice in Iowa. In contrast, a Norway rat in the Hong Kong sewers would be the same species as a Norway rat in New York.-- OBSIDIAN†SOUL 00:56, 5 February 2012 (UTC)

Rabbits certainly number in the billions, though they aren't a single species either. I'm sure there are some vertebrate fish like herring that would give us a run for our money (according to the herring article there can be up to four billion in a single school)

. And there were 24,000,000,000 chickens as of 2003. 112.215.36.185 (talk) 05:15, 5 February 2012 (UTC)

fish are vertebrates, right? Surely there are several species of small fish hat have a larger population than 7 billion. --Lgriot (talk) 00:43, 6 February 2012 (UTC)

Gonostomatidae (a family of deep-water marine fish) says: "Cyclothone, with 12 species, is thought to be (along with Vinciguerria), the most abundant vertebrate genus in the world." See also http://www.nefsc.noaa.gov/faq/fishfaq1.html#q5. I guess it's hard to estimate how many billion small fish there are in deep water around the world. PrimeHunter (talk) 03:01, 7 February 2012 (UTC)

back muscles

When I lean backwards whilst standing, my abs and (to a lesser extent) chest muscles flex to help me maintain position. When I lean forwards my back muscles do the same. So why, after carrying a heavy backpack all day, do my back muscles hurt and not my abdominal/chest muscles? This seems counter-intuitive. The Masked Booby (talk) 14:43, 4 February 2012 (UTC)

DIdn't you just answer your own question? With a backpack on, you lean forward. 79.122.74.63 (talk) 15:21, 4 February 2012 (UTC)

Both muscle groups would have to act with each other to stabilize your backpack, so both would be working. A backpack is fairly efficient, though, so the group to feel the most soreness would be the group that is least used to this type of heavy work. For me at least, my that mid-lower-back area doesn't see a lot of heavy or long-term exertion, even in any sport I play. SamuelRiv (talk) 18:52, 4 February 2012 (UTC)

Is it possible to improve vision with eye exercises

my friend told me that it is possible. if it is then please tell me some eye exercises Rahul^{Text me} 15:08, 4 February 2012 (UTC)

Bates method. (Googling "eye exercises" leads you to loads of pages, including a wikihow site.)--TammyMoet (talk) 15:31, 4 February 2012 (UTC)

I personally used to use the Bates method, because my initial experience with it was surprisingly good. I tried palming, and afterwards my vision was noticeably clearer for a little while (less than a minute). I started believing the claims, but no matter what, it doesn't do much in the long term. Once I did manage to shave about a diopter off my prescription, but there is no way of knowing if that was just because my eyesight was unnaturally bad due to stress, or whether it was some other effect of the treatment. Also, the eyesight eventually went back to what it was. When I finally read the research, I gave up pretty quickly, regardless of the initial experience. IBE (talk) 15:54, 4 February 2012 (UTC)

If the Bates method is of any value at all, is it that it reminds one that the eyes focus by the means of muscles and if they don't get enough exercise they weaken. I can understand IBE's comment because I can't say that his (Bates) exercises appeared to do me any good when I tried them. Yet, I noticed after I stopped working in an office (where every-day I was only focusing 10 – 15 ft at the most and most of the time a lot shorter and a similar amount in the evening glued in front of the TV) that my eyesight improved to the point where I forgot to wear my specs because I could see well enough without them. Maybe also, because I then needed to take notice of vertical line as well as horizontal that my bad astigmatism became negligible. Thus, I think that just doing a few exercises from time to time it not really enough to make a major improvement, as they don't exercise the muscles enough. Also, as one grows older, atrophy of muscles, due to lack of exercise, takes less time to occur. Extended Bed Rest Accelerates Muscle Deterioration In Older Adults. Some might consider this last comment trite, but older friends of mine that have only spent a few hours in the Pub, focusing no further than the bar-maid, come out, unable to see their way home – and back to the wife. I tell you -this is the truth. Old age is not very kind – so don't go there. --Aspro (talk) 19:59, 4 February 2012 (UTC)

Vitamin D may also be beneficial to eye health. Count Iblis (talk) 00:00, 5 February 2012 (UTC)

Weakening of the ciliary muscle with age, which regulates the accomodation reflex, tends to result in presbyopia, or reduced ability to focus on near objects. There is definitely variation in ciliary muscle strength between individuals of the same age, so any valid eye exercises may focus (no pun intended) on these muscles. ~AH1 ^(discuss!) 01:25, 5 February 2012 (UTC)

Why can animals be classified as vertebrates or invertebrates if vertebrates only make up one phylum?

I simply don't understand why scientists have to classify animals as vertebrates or invertebrates. Invertebrates make up several phyla, while vertebrates are in only one phylum? Yes I know humans are vertebrates, and that fact can lead to bias (like the Old World and New World stuff) but remember, not all chordates are vertebrates. Was it done for the sake of convenience, or just because chordates are somehow special? And what current phylum has the most similarities with chordates? Narutolovehinata5 ^tccsdnew 15:23, 4 February 2012 (UTC)

Scientists classify things in whatever ways they think will be useful. Vertebrates have a lot of similarities to each other that they don't have with invertebrates, which makes it a useful classification. You won't find scientists talking about invertebrates much since, as you say, they are so varied - you would want to talk about a specific subset of invertebrates. The word only exists to distinguish them from vertebrates, rather than as a classification of its own. --Tango (talk) 15:54, 4 February 2012 (UTC)

Of course, there is a discussion of this very topic in Wikipedia: Invertebrate#Significance_of_the_group. --Tango (talk) 15:58, 4 February 2012 (UTC)

(WP:EC)See Invertebrate#History and Invertebrate#Significance_of_the_group. The term was coined by Lamarck, who himself is responsible for making further taxonomic subdivisions (Linneaus apparently divided all invertebrates into insects and worms). The article goes on to say "the (invertebrate) grouping has been noted to be "hardly natural or even very sharp."" Suffice it to say, it is a useful term for casual conversation, and does reflect some bias, but is not really used with much scientific weight. Also, just to clarify: "invertebrate" is not a "classification", it has no place in taxonomy or phylogeny, and as you point out the group is highly paraphyletic. It has the same scientific level of rigor as a term like "Non-ant insect". In short, the term is still used because it is useful, and is fairly well-defined. SemanticMantis (talk) 16:09, 4 February 2012 (UTC)

Right. Classifying animals as vertebrates and invertebrates is a bit like classifying people as Americans and foreigners. If you live in America the classification is useful, but it is not a very meaningful distinction from a global point of view. Looie496 (talk) 23:57, 4 February 2012 (UTC)

It's a very old classification system, back when people didn't truly appreciate the vast differences between groups of organisms and were still a bit anthropocentric in that they consider vertebrates to be more important than anything else (after all, they are usually the largest organisms). Today, Invertebrata is not a formal taxonomical rank (note its article does not have a taxobox in contrast to subphylum Vertebrata). It's merely a colloquial grouping meant to quickly distinguish vertebrates from non-vertebrates.-- OBSIDIAN†SOUL 00:51, 5 February 2012 (UTC)

On the similarity thing, echinoderms are the only deuterostomes other than the chordates and were said (at least when I was in high school 15 years ago) to be the phylum most closely related to chordates (and by "most closely related," I think I mean that on a cladistics graph, they branch most closely to or in concert with chordates in some fashion or another). DRosenbach ^{(Talk | Contribs)} 06:14, 7 February 2012 (UTC)

Basic iTunes question

Sorry, this is really basic, and please transfer it to Entertainment RD if that's more appropriate. I am gradually ripping all my CDs and putting them onto an iPod, using iTunes. It is taking up more space than I would like on my hard drive. If the music is safely on the iPod, how can I easily take them off the hard drive, or compress them, or whatever? ITunes seems to want me to have everything on both the hard drive and the iPod, "synchronised". Thanks. Itsmejudith (talk) 18:31, 4 February 2012 (UTC)

You would probably be better off on the Computing desk. --Tango (talk) 19:02, 4 February 2012 (UTC)

(ec)You might do better at the Computing desk than either! Not having used it, my hazy understanding of iTunes is that it is mostly for copy-locked (DRM) music files rather than for the all-purpose files from a ripped CD, and so a simple general purpose sound playback program might do better. But the extent of my musical forays nowadays is YouTube running Video DownloadHelper (with NoScript to block the VEVO ads ;) ) Wnt (talk) 19:04, 4 February 2012 (UTC)

This is not true at all. You can use iTunes to manage any MP3s or other media files. They don't have to be DRMed at all, and usually aren't if you are ripping them from your own CDs (which you can do within iTunes easily). They are only DRMed if you get them through the iTunes store, which you're under no obligations to do. I don't think anybody cares about how you pirate music and I'm not sure why you offered that up as an answer. --Mr.98 (talk) 20:59, 4 February 2012 (UTC)

I thought most/all? music downloaded from iTunes is DRM free by now? Nil Einne (talk) 07:42, 5 February 2012 (UTC)

Pirate? Why, how can I possibly pirate music by downloading it from the authorized publisher publishing from his official YouTube account? Wnt (talk) 03:53, 5 February 2012 (UTC)

It depends greatly on your local laws. Nil Einne (talk) 07:43, 5 February 2012 (UTC)

You can set iTunes to "Manually Sync" your iPod. That way, it won't attempt to automatically make the two libraries match every time you plug it in. You can then safely delete music from your computer's hard drive, without affecting the iPod as long as you don't try to sync the whole music library manually. Usually, I prefer to set it to Manual and only select specific playlists to sync to my iPod. As long as you keep that music on your computer's hard drive, it won't have any problems. — The Hand That Feeds You:^Bite 19:15, 4 February 2012 (UTC)

You can also just set it to manually manage (not sync at all). Set up in this way, you move music to the iPod by dragging it within iTunes. You can then delete it off of the main computer if you want. --Mr.98 (talk) 20:59, 4 February 2012 (UTC)

Thanks folks. Itsmejudith (talk) 20:52, 5 February 2012 (UTC)

Resolved

Parrots (e.g. Amazon)

Is it true that male Amazon Parrots usually get on better with women and that female Amazon Parrots get on better with men? Something to do with pheromones? Thanks.

Also (I asked this before but I don't think I got an answer, can't find the question now), is it just a coincidence that a baby Goffin's Cockatoo makes a noise that sounds a lot like a human baby? e.g. like http://www.youtube.com/watch?v=zLAp98VVuao --95.148.105.157 (talk) 21:50, 4 February 2012 (UTC)

binary star info

Can someone give the formula including 3 numbers: solar mass of both stars, separation distance, period. So if i was given 2 out of the numbers i can figure out the other one. So a formula that including all of 3 info above. Thanks!Pendragon5 (talk) 22:50, 4 February 2012 (UTC)

The separation distance isn't necessarily constant, for elliptical orbits. StuRat (talk) 00:07, 5 February 2012 (UTC)

The deviation of an elliptical orbit from perfectly circular is known as its orbital eccentricity, where a value of 0 is a circle and 1 is a parabola. The average distance between two objects is the semi-major axis, and the centre of gravity between a system of gravitationally-bound objects is its barycenter. You may try finding some 2-body simulators online, as the mass of either object does affect the shape of the orbit, or compare some real-life examples such as Capella versus Epsilon Aurigae. ~AH1 ^(discuss!) 01:15, 5 February 2012 (UTC)

I need a formula.Pendragon5 (talk) 02:14, 5 February 2012 (UTC)

And let assume that the separation distance is constant.Pendragon5 (talk) 02:34, 5 February 2012 (UTC)

According to Standard_gravitational_parameter#Two_bodies_orbiting_each_other, the relationship is 4π²r³/T² = G(m₁ + m₂). 98.248.42.252 (talk) 03:06, 5 February 2012 (UTC)

I was going to derive it from scratch, but then saw Kepler orbit. Basically looks like the standard Kepler equation, and just set all eccentricity terms (e, E) to zero. SamuelRiv (talk) 03:32, 5 February 2012 (UTC)

I don't think this equation, 4π²r³/T² = G(m₁ + m₂), is what i'm looking for. I'm looking for the equation include the solar mass of the stars, the period of the star (how much time it took for them to orbit each other once), the separation distance.Pendragon5 (talk) 19:51, 5 February 2012 (UTC)

See below. That's the exact equation you are looking for, as m1 and m1 are the masses, G is the "big G" gravitational constant, r is their seperation distance (as measured from their centers), and T is their orbital period. I've explained in more detail below, with links, before I knew you also asked it up here. --Jayron32 20:49, 5 February 2012 (UTC)