Wikipedia:Reference desk/Archives/Science/2018 November 30

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November 30

Question on Adaption

At the cellular level, how do adaptions occur if the organisms which perpetuate these adaptions do not possess the ability to know or percieve the external pressures that they are adapting to? The evolution of feathers for insulation in dinosaurs is one example. What is actually going on down there? How is the cold and the dangers presented by it being reacted to in such an efficient way, as if genes had a mind of their own? déhanchements (talk) 03:29, 30 November 2018 (UTC)

Gene-centered view of evolution may help. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:16, 30 November 2018 (UTC)

It doesn't happen in an efficent way. Mutations (which is a more relevant article) happen randomly; the useful ones help the organism survive and so are the ones we see spread through the fossil record; the detrimental ones lead to a quicker death. Henry^Flower

Not necessarily just living and dying. A mutation that tripled the organisms overall success at reproduction would spread even if it halved the organisms expected lifespan. Conversely, a mutation that increased lifespan while decreasing overall reproductive success would probably not spread. --Khajidha (talk) 16:45, 1 December 2018 (UTC)

Microscopic bugs, in color

You know those teensy bugs we see in shades of grey with electron microscopes? Are they colourful like a lady bug or emerald ash borer? Anna Frodesiak (talk) 06:52, 30 November 2018 (UTC)

When I have seen these tardigrades they are usually pretty colourless and transparent, or slightly yellowish—which may be due to what they ate! Graeme Bartlett (talk) 08:26, 30 November 2018 (UTC)

Hi Graeme. Ooooooh, transparent or yellowish, eh? Well, what about those mites and all those other creepy-crawlies we see walking about? I'm kind of guessing they're pretty blind, so might not need colour. I'm not a good guesser, though. Anna Frodesiak (talk) 08:41, 30 November 2018 (UTC)

Well mites I have seen are dark, green or red. I imagine they come in all sorts of colours to camouflage against what they live on. The dust mite looks white in the pictures. Graeme Bartlett (talk) 10:44, 30 November 2018 (UTC)

The dust mites have pink feet, like shrimp. Is that real colour? And do they need colour? Can tiny predators see? Anna Frodesiak (talk) 11:12, 30 November 2018 (UTC)

There were some awesome tardigrades in Ant-Man and the Wasp, but, you know, WP:FILMSCI. Gråbergs Gråa Sång (talk) 10:56, 30 November 2018 (UTC)

[1] says

Tardigrades are often white, or colourless and more or less transparent; some are brown, yellow, orange, pink, red or green. The body colour can reflect the pigmentation of the body cuticle itself, or can be due to the gut contents showing through the colourless body wall.

Nil Einne (talk) 12:02, 30 November 2018 (UTC)

A similar statement is made in the abstract here [2] although weirdly I can't see where it's made in the article. According to [3] and [4], Ramazzottius varieornatus is one example of a pink tardigrade, at least along its back. Nil Einne (talk) 12:14, 30 November 2018 (UTC)

Thank you, all! :) Anna Frodesiak (talk) 17:28, 1 December 2018 (UTC)

Eyebrows

Are these the ones on our eyebrows?
No these are dust mites, living in dust in the pillow or floor.

Anna Frodesiak (talk) 11:13, 30 November 2018 (UTC)

• Demodex folliculorum and Demodex brevis Graeme Bartlett (talk) 12:16, 30 November 2018 (UTC)

Gross! Hey, I found a pic for brevis at commons. Yay!....and gross! Anna Frodesiak (talk) 23:18, 30 November 2018 (UTC)

Plants that produce sound

Which plants are known for producing sound? Poplars come to mind, though I do not know if any particular species is "louder" than others. I suppose a lot of grasses rustle in the wind too. Surtsicna (talk) 14:17, 30 November 2018 (UTC)

It depends what you mean by producing sound. Practically any plant will rustle if it's big enough and there's enough wind. There are a large number of plants with exploding seed pods. See [5].--Shantavira|^{feed me} 15:01, 30 November 2018 (UTC)

Monica Gagliano, a plant physiologist at the University of Western Australia claims that corn seedlings emit a 220 Hz purr[6]. The leaves of pine trees and Douglas firs occasionally make a pop sound as they clear an Air embolism from their Xylem (water transport tissue). Lois Wardell of Arapahoe SciTech in Tucson and geophysicist Charlotte Rowe detect "squawks" from Saguaro cactus that may signal "I'm cold" or "I'm really thirsty".[7]. Gagliano notes Shamans' claims to learn from plant sounds and speculates that plants may communicate by sound vibrations even though they lack structures resembling a mouth or ears. DroneB (talk) 15:22, 30 November 2018 (UTC)

I mean producing sound that is clearly audible and pleasant to humans. Poplars rustle under the slightest wind, practically even when we cannot feel the wind. Perhaps I should emphasize that I am asking about plants that are notable for the sound they produce or commonly associated with it. Surtsicna (talk) 15:36, 30 November 2018 (UTC)

The Wind in the Willows (although to be fair, willows and poplars are both cousins in the Salicaceae family). Alansplodge (talk) 16:33, 30 November 2018 (UTC)

Screaming Trees? Martinevans123 (talk) 16:36, 30 November 2018 (UTC)

If you search for "creaking trees" on YouTube there are pages of results, many of which claim to be "relaxing". I'm not sure that any tree species creaks more than any other. Alansplodge (talk) 16:46, 30 November 2018 (UTC)

I had my doubts about hearing corn grow on a still night, until I did a consulting job in Indiana and stood next to a cornfield on a windless night. --Guy Macon (talk) 17:28, 30 November 2018 (UTC)

By corn do you mean maize? DuncanHill (talk) 23:31, 30 November 2018 (UTC)

The word "corn" in the context of a trip to the U.S. state of Indiana has zero ambiguity. Stop being pedantic. If I had told a story about a trip to Hertfordshire, I would have used UK English. --Guy Macon (talk) 23:46, 30 November 2018 (UTC)

Christ, someone got out of bed the wrong side! DuncanHill (talk) 23:51, 30 November 2018 (UTC)

Yeah, stop being so pedantic, Duncan, ya doofus. It'll soon be Christmas. Martinevans123 (talk) 23:55, 30 November 2018 (UTC)

And this page is off my watchlist. You can do the reverting and asking for page protection. Not worth bothering with any more. DuncanHill (talk) 00:00, 1 December 2018 (UTC)

Wow. Yeah looks like he meant maze. But glad you've managed to escape. Martinevans123 (talk) 00:07, 1 December 2018 (UTC)

I don't know how pleasant one might consider it, but some plants, such as witch-hazel, release their seeds with an audible popping sound. See Dehiscence (botany). And I just noticed that Shantavira alredy mentioned this above. Deor (talk) 19:26, 30 November 2018 (UTC)

Well don't tell the trees Deor, 'cause the trees don't need to know. Martinevans123 (talk) 20:59, 30 November 2018 (UTC)

I wonder if Surtsicna is referring to aspens (Populus tremuloides, Populus tremula)? They are known for their constantly fluttering leaves. Apparently P. tremula is sometimes known in Welsh as coed tafod merched, 'the tree of the woman's tongue'. (Source: Broadleaves by the Forestry Commission, 1985, p56, isbn 0-11-710039-0). PaleCloudedWhite (talk) 22:03, 30 November 2018 (UTC)

To illustrate what others have said about popping seedpods, this video, although not RS, might be of interest. PaleCloudedWhite (talk) 22:15, 30 November 2018 (UTC)

Oi Paley. Even in parts of Berkshire and in Manx also, it seems. Martinevans123 (talk) 23:38, 30 November 2018 (UTC)

"Manx for that". PaleCloudedWhite (talk) 09:21, 1 December 2018 (UTC)

Yes, I meant the entire Populus genus. Surtsicna (talk) 23:46, 30 November 2018 (UTC)

A different method of noise production occurs in bladderworts (Utricularia spp.), though whether this is pleasant, rather than just interesting, is debatable. "If you ever remove a bladderwort plant from the water, you may be surprised to find audible crackling noises as the bladders get triggered shut".[8] PaleCloudedWhite (talk) 09:17, 1 December 2018 (UTC)

Rhubarb can be heard 'squeaking' as it grows ("the farmer, Janet Oldroyd-Hume, said that if you stood quietly you could hear the rhubarb grow: the gentle pop of a bulb, the creaking of a stem"[9] "it's really true that you can hear it eerily creaking or squeaking in the darkness as it pushes its way through the soil!"[10] PaleCloudedWhite (talk) 10:23, 1 December 2018 (UTC)

True story. Here's rhubarb (without any Custard): [11]. Martinevans123 (talk) 15:49, 1 December 2018 (UTC)

Memorizing constants/values for exams in college?

I assume no one can be expected to know in an exam that e = 2.7182818284590452353602874713527. But how far should we go? In the case of Pi, is using a value of 3.14 enough? Is rounding 9.80665 m/s2 to 9.8 or even 10 a safe approximation? Doroletho (talk) 18:16, 30 November 2018 (UTC)

In my day, examination questions used to state what approximation to take for such constants, or more often asked for exact answers in terms of e, pi or g. Are modern children expected to learn any of these? Are there many exams these days where calculators are not allowed? (I do recall a question on a JMB Physics special paper that I sat in the days of slide rules. No constants were given, and the question just asked "Estimate the heat loss from a typical house in Manchester in the middle of winter". I just happened to know the relevant coefficients of thermal conductivity, so I went to town on that question.) Dbfirs 18:27, 30 November 2018 (UTC)

Whether or not a teacher or professor expects you to memorize values like this depends entirely on how much of an asshole they are, with there being a direct assholery-to-memorization relationship. For the most part, these values can be looked up if needed to greater than 2-3 digits, and even so, most major exams have reference tables with values of common constants, etc. For example, here is the reference tables for the NY Regents exams, here is the one used for the Advanced Placement Physics exam, etc. Most major standardized tests just give you such information. If you're expected to memorize anything, 2-3 digits will suffice. I've never heard of a job where a person was required to memorize numbers in real life. If they need the value, you can google it and get it to whatever accuracy you want. Pi = 3.14 works for any multiple choice test (heck, for most multiple choice tests, 3 works fine, since usually only 1 of the 4-5 answers is usually close enough). When I teach physics, I tell students, for multiple choice questions, just use 10 for gravity. It gets close enough. --Jayron32 19:31, 30 November 2018 (UTC)

The constants and conversion factors in the APP sheet are all wrongly stated as exact numerical values. Ways to show that values are rounded include replacing = by ≈ (almost equal sign), ellipsis ... to show trailing digits or a footnote such as "to 3 significant figures". It quotes the Speed of light, 3.00x10⁸ m/s "effective 2015" when in reality since 1983 the speed of light in vacuum has by definition been exactly 299,792,458 m/s. One hopes Jayron's students find out that "just use 10" gravity has units m/s² of acceleration. DroneB (talk) 00:26, 1 December 2018 (UTC)

Didn't some of the New York tests mention 22/7 or was that just my teacher? Sagittarian Milky Way (talk) 20:48, 30 November 2018 (UTC)

Sagittarian Milky Way: 22/7 is an excellent approximation for Pi, the ratio of circumference to diameter of a circle. Dolphin (t) 01:24, 1 December 2018 (UTC)

It's close for such a small denominator (better than 314/100) which locks out the other small denominators from being closer and algebra prefers fractions so no wonder teachers tell you about it. The next fractions that are closer are apparently 179/57 then 201/64 which aren't that much lower error than 22/7. Sagittarian Milky Way (talk) 02:02, 1 December 2018 (UTC)

355/113 is much more notable. Not only does it repeat odd digits in a notable way, but it's within 1/3,000,000 of the true value. --76.69.46.228 (talk) 19:16, 3 December 2018 (UTC)

I think it is useful to know the most important constants to 1-3 significant digits (3.14, 2.7, 9.81, 6e23, 22.4 are the ones that come to my mind) to be able to do Fermi approximations, to get an idea of the scale of a problem. But I'd never ask student to memorize theses numbers - that's what paper (or silicon) is for. --Stephan Schulz (talk) 21:12, 30 November 2018 (UTC)

It will vary according to the examining body, who should make clear their requirements in advance. For example, for my A Levels some boards allowed the use of log books which included a variety of physical constants, and formulae, others did not allow their, use and one needed to memorise some constants to a given number of significant figures. This was set out in the syllabus and taught to us by our lecturers. I would advise the OP to ask their lecturers what the requirements are for their various courses and exams. DuncanHill (talk) 21:17, 30 November 2018 (UTC)

Rounding g to 10 m/s/s is probably a bit slack. In real engineering work I use 9.81 m s-2. In the absence of any specific guidance you should get a clue from the number of significant figures in the problem that is set. Incidentally at my uni we had standard data books that we used in exams, chock full of exciting numbers like e and g and steam tables and material properties and so on. Greglocock (talk) 22:30, 30 November 2018 (UTC)

One of the most useful lessons to learn in physics at High School is that we are deluding ourselves if we think our answers deserve any more than three significant figures - see False precision. (I failed to learn that lesson until a couple of years after High School!) Consequently, no teacher should encourage students to memorise any physical constant to more than three significant figures. e is 2.72 and pi is 3.14. This will help students realize that if more significant figures are required, human memory is not sufficiently reliable and a written source should be consulted. Dolphin (t) 00:48, 1 December 2018 (UTC)

I was spending first ~6 months of 7th grade memorizing pi for fun and didn't find out I remembered wrong till high school (3.14159265358979326, not 3.1415926535897936) Sagittarian Milky Way (talk) 02:32, 1 December 2018 (UTC)

And you'd still be wrong. ...8979323846 :) DMacks (talk) 17:15, 1 December 2018 (UTC)

According to the Old Testament (1 Kings, 1:27), π = 3. Some highly educated friends (PhD, Princeton) tell me that said manuscript is divinely inspired and inerrant.

I have, in my infancy, decided that it is ancient fake news, but not everybody agrees.

My theory , however, is falsyfiable. π has been around since the well known π-thagororas - a rational and polydigital mathematician - invented it. Of course, π possibly was a much overrated thinker when compared to the stable geniuses of the current era. --Cookatoo.ergo.ZooM (talk) 17:14, 1 December 2018 (UTC)

The Greek letter π was originally an abbreviation of the Greek word for periphery (περιφέρεια) and later in 1706 for perimeter (perimetros περίμετρος) , but not for Pythagoras (Πυθαγορας). DroneB (talk) 23:47, 1 December 2018 (UTC)

The correct verse is 1 Kings 7:23. What it says is that the circumference all around the brim was 30 cubits with a (not-mentioned) diameter of 9.55 cubits. In addition, there was apparently a flat ledge extending out from the brim that was supported by "knops" (ornamental knobs). It appears that the ledge's outer diameter was 10 cubits with a (not-mentioned) circumference of 31.4 cubits. To illustrate, any overfilling would result in contents flowing over the brim onto the 0.45 cubit wide ledge. Akld guy (talk) 18:53, 1 December 2018 (UTC)

There is nothing in the text saying anything about protruding knops. However, all the measurements in that verse (and the rest of the description of the temple) are given as whole cubits, and it is possible to have a circle with dimensions that when rounded to the nearest whole number give a diameter of 10 units and a circumference of 30 units. He made the Sea of cast metal, circular in shape, measuring ten cubits from rim to rim and five cubits high. It took a line of thirty cubits[o] to measure around it. Iapetus (talk) 10:44, 3 December 2018 (UTC)

I didn't say anything about the knops protruding, and it's impossible to tell from your reply whether you understood what I said. Let me say it again. There was a circular sea (like a bowl or wok) that had a stated circumference around its rim of 30 cubits. We assume therefore that the diameter was 9.55 cubits. From verse 7:24, we can deduce that a horizontal ledge extended out from the rim, all the way around. This ledge had a stated (outer) diameter of 10 cubits, and it was supported by knops attached underneath to the sea all the way around. Therefore there is no discrepancy in trying to relate the 10 cubit diameter to the circumference of 30 cubits. They are referring to two different things, the inner circumference of the ledge (30) and its outer diameter (10). If you compute the difference, you find that the ledge was about 0.45 cubits wide (10-9.55). Akld guy (talk) 19:17, 3 December 2018 (UTC)

How has this discussion, including both fact and folly ideas, gone this far without mentioning the Indiana Pi Bill? DMacks (talk) 17:18, 1 December 2018 (UTC)

• For e, I was told ~10 years ago the absolutely stupid mnemonic that it is 2.7 followed by twice Leon Tolstoi's year of birth (1828). It is absolutely stupid because chances are you never knew Tolstoi's year of birth or forgot it, yet because of the way my brain is wired I remembered both that e=2.718281828 and Tolstoi's DOB. (Neither fact has been of any use so far.) Tigraan^{Click here to contact me} 18:55, 1 December 2018 (UTC)

My teacher said square root of 3, Washington's birth year. Sagittarian Milky Way (talk) 20:05, 1 December 2018 (UTC)

My (physical) mailing address at one time included the nearest integer to 1200/ln(2), a factor useful for Cent (music) notation. —Tamfang (talk) 10:14, 3 December 2018 (UTC)

About 4.7*10^(30) hydrogen atoms will fit on a perfect circle with the radius of the galaxy, so if we get pi right to within a fractional error of less than 2*10^(-31), we can compute the radius of such a circle as measured by the number of hydrogen atoms one can put on it as an exact integer. An absolute error of 6*10^(-31) would then suffice, that level of accuracy was obtained for the first time by Ludolph van Ceulen in the late 16th century. Count Iblis (talk) 20:01, 1 December 2018 (UTC)

When Tigraan said "twice Leon Tolstoi's year of birth (1828)" I was puzzled until I realised that he meant "write 1828 twice". 62.49.80.34 (talk) 09:12, 3 December 2018 (UTC)

Some people are into memorizing pi to 100s of places as a hobby, but for mental and BOTE calculation purposes it's handy to know some constants to two or three digits at most. Pi, e, logs and square roots of small integers, physical constants like the speed of light and acceleration of gravity, etc. There are usually tables of such constants in the backs of the relevant textbooks. Back when I took tests in such subjects, the necessary values were usually provided. If those numbers come up in your calculations a lot they will tend to stick in your mind, so I used to know a bunch of them without explicit memorization. I still remember a few. 173.228.123.166 (talk) 07:46, 7 December 2018 (UTC)

Chemical education.

So recently someone told me that all Bronsted-Lowry acid/bases are a type of Lewis acid/bases. So all proton transfer reactions have an electron-transfer reaction but not all electric-transfer reactions have a proton-transfer reaction. Does anyone disagree with this? If it were up to me, I'd think it'd make more sense to put the Lewis acid/base chapters with the oxidation-reduction transfers, rather than with the Bronsted-Lowry acid/base chapters, and if it were also up to me, teach Gen Chem students about Lewis acid/bases before Bronsted-Lowry acid/bases. I think there's this big book by Linus Pauling in 1970 that services as a general model as to how Gen Chem textbooks are written, so somewhere along the line, Lewis acid-bases are not taught with oxidizing/reducers.

From the guy who previous asked "Is it a contradiction to be a strong Lewis acid (receive electrons) and a strong reducing agent (loses electrons) at the same time? And is it a contradiction to be a strong Lewis base (loses electrons) and a strong oxidizing agent (causes others to lose electrons) at the same time?" which can be found here https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2018_January_17#Chemistry_question. Thanks. 67.175.224.138 (talk) 21:06, 30 November 2018 (UTC).

Yes, all B-L acid/base reactions can be also expressed as a Lewis acid/base reaction. With Lewis reactions, I'm not a fan of the "donor" or "transfer" language, as it doesn't really capture the situation as well as other terminology. Lewis acid-base reactions are bond-formation reactions whereby an atom that has a lone pair of electrons forms a new bond (via that lone pair) with an atom that has an empty orbital. This bond is sometimes called a coordinate covalent bond, to distinguish it from other 2-electron covalent bonds whereby each atom on either side of the bond contributed one electron to the bond. The electrons aren't donated or transferred per se (as that would imply they left their original atom) but instead simply form a new 2-electron bond with the Lewis acid atom. A B-L acid/base reaction is a great example of this, as the B-L base forms a new bond with the H⁺ ion using this exact mechanism. That's why B-L bases are also Lewis bases. Since, however, Lewis bases can form bonds to other atoms besides hydrogen, it's a broader category than B-L bases. --Jayron32 11:57, 3 December 2018 (UTC)