Why the sentence in Newton's theory of gravitation of article Gravity is "most modern non-relativistic gravitational calculations are still made using Newton's theory because it is simpler to work with and it gives sufficiently accurate results for most applications involving sufficiently small masses, speeds and energies." instead of "most modern non-relativistic gravitational calculations are still made using Newton's theory because it is simpler to work with and it gives sufficiently accurate results for most applications involving sufficiently small masses, speeds or energies."? Does it mean that at least the three prerequisites must be met simultaneously then Newton's theory can be applied? - Justin545 (talk) 05:49, 3 August 2020 (UTC)[reply]

It just means that Newtonian gravity is perfectly adequate except in some highly specialized applications. Unless you're measuring the defect in the orbital precession of Mercury or making fine adjustments to atomic clocks on satellites (and most people aren't) then Newtonian mechanics works fine. --Jayron32 06:24, 3 August 2020 (UTC)[reply]

Mercury moves at low speed (compared with the speed of light) but has a large mass and large kinetic energy (if I understand correctly). According to the sentence, Newtonian gravity is not adequate to accurately predict Mercury's orbit since the mass and energy criteria are not met, isn't it? Because of the "and" in the sentence, 3 criteria (mass, speed, energy) must be ALL met (all of them must be small) or Newtonian gravity cannot give sufficiently precession, right? In other words, Newtonian gravity is inadequate for precisely calculating anything about Mercury because the mass of Mercury is not small in all cases (even if it has small speed and has small energy), right? - Justin545 (talk) 08:36, 3 August 2020 (UTC)[reply]

See Tests of general relativity#Perihelion precession of Mercury. It's the distance to the Sun that leads to a measurable deviation; essentially the gravitational attraction is close enough for deviations to just barely be noticeable with Mercury. It's very small, but real, on the order of 40 arcseconds per hundred years; given that an arcsecond is 1/1296000 of a revolution, we're talking a deviation of a few dozen ppm per 100 years. What's more impressive is not that GR is needed to explain the deviation, but that the deviation was measured in the 19th century. You're focusing too much on the individual words here. Newtonian gravity works in cases except where the values become large enough for the deviations between GR and Newton to show up in significant figures of whatever the tolerances of your measuring devices you need to use are. For you, dropping a ball on earth, and making measurements with a chronometer and a ruler, this is way out of the tolerances of your measurement, so use Newton. Even for the Earth-Moon system, Newton works fine in most cases. Look at the equation of gravity according to Newton: F = G * (m₁*m₁/r²). The only values that matter are m and r. G is a constant that just makes the units work out, so we can ignore it. The only times where General Relativity needs to be used is when 1) The values of m and r are extreme (large values of m and small values of r) and 2) Where relativistic effects significantly alter the values of m and r (in things like time dilation or length contraction, or mass-energy equivalence) and those values only show up at high speeds (which is the same thing as high kinetic energy) or high potential energy (high forces). Since gravitational force (potential energy) increases with high masses and short distances, that just the same as what I said at #1. If you're wondering how GR deals with these forces, it doesn't. It doesn't treat gravity as a force, it treats it as a warping of spacetime itself, and treats objects with a large mass at a close distance as though they are moving in straight lines at a constant speed through a distorted spacetime. There is no force of gravity in GR. This kind of warping of geometry is fantastically mathematically complex; it took Einstein something like 10 years to formalize General Relativity because he had to wait for people like Minkowski and Hilbert and Lorentz and the like to literally invent the mathematics that he needed to do the calculations right. So, if you want to do gravity calculations, you can either do this insanely complicated tensor calculations, or you can do simple algebra. If the difference between the two methods doesn't show up on your measuring devices, and you literally could not tell the difference between the two results in a real physical sense, then use Newton's equation. The various relativity equations only shows up at speeds close to the speed of light, and near very large masses. The reason why satellites need to correct for this is because they are at a different distance from earth than you are, so their clocks run at a slightly different rate than yours; on the order of a few ppm, which seems small but can amount to several meters in a day, and several kilometers over the course of a year. When you're using those satellites for doing things like guiding your car on a road, or guiding a bomb to its target, you don't want it to drift that much. --Jayron32 18:02, 3 August 2020 (UTC)[reply]

Okay ... basically, I though every sentence in the article is supposed to be correct, so readers are not misled by the contents. Because I am not familiar with relativity and the conjunction looked odd to me, so I was trying to confirm it here. I would directly modify the article and correct the conjunction if it were confirmed to be wrong. Although the condition is that they need to be small, I didn't see an explicit statement is about how small should they be. Which may be the source of ambiguities where formulas and equations should kick in. - Justin545 (talk) 07:40, 4 August 2020 (UTC)[reply]

English is not as restrictive as boolean operators in terms of the meanings of conjunctions, and I don't find the use of "and" confusing here. I don't generally read "and" to mean "only and" unless the additional qualifiers are there. --Jayron32 15:43, 4 August 2020 (UTC)[reply]

If your concern is in regard to grammar, then either wording is fine. One can be calculating speed and energy; or, one can be calculating either speed or energy. In either case Newtonian (non-relativistic) physics equations provide "sufficiently accurate results for most applications...". 2606:A000:1126:28D:E00A:A68D:43D6:44E1 (talk) 07:23, 3 August 2020 (UTC)[reply]

Yes, my concern is the conjunction. I want to know that it should be "and", "or" or "and/or"... - Justin545 (talk) 08:50, 3 August 2020 (UTC)[reply]

All three must be met. If the mass of an involved body is huge, the warping of spacetime may become non-negligible. Large differences in potential energy show up as gravitational time dilation not accounted for by Newton's Laws. And high speeds give rise to velocity time dilation. The last two are large enough that they have to be taken into account to make the GPS system work. So the appropriate conjunction is indeed “and”.  --Lambiam 08:34, 3 August 2020 (UTC)[reply]

Thanks for the answer. - Justin545 (talk) 08:50, 3 August 2020 (UTC)[reply]

Newton is good enough that no one thought anything was off till about 2 centuries of good telescopes. Degenerate stars need relativity for short term naked eye stuff. Sagittarian Milky Way (talk) 14:22, 3 August 2020 (UTC)[reply]

Excuse me Justin, but if you are not familiar with relativity, how can the conjunction seem odd to you? You must assume that the sentence is right and conclude that an inclusive 'and' is meant (which as a matter of fact is true: if speed is large OR mass is large OR energy is large then newtonian equations will not deliver accurate results, so mass AND speed AND energy have to be small). But here I see a bigger problem: every statement in WP is supposed to be based on some source, so if any source was given in this article, you would have checked there whether 'and' or 'or' is correct. But if you had to ask here, there is probably no source given and the sentence is an original research of the original editor, which is forbidden in WP. Of course many editors do find that their own O.R. is not O.R. but a direct conclusion from general knowledge. I, more an user of WP than an editor, I do prefer that every claim in WP to be validated by some source. 2003:F5:6F0C:E600:487C:DA02:59F5:AE62 (talk) 20:08, 8 August 2020 (UTC) Marco PB[reply]

...Nobody dared to raise a concern about the Oxford comma? Nimur (talk) 17:28, 3 August 2020 (UTC)[reply]

Recently, I have noticed that nearly any person with attached earlobes I have seen either in real life or in the media was slender, as a matter of fact. Now, as I was unable to find any pertaining scientific evidence on this issue, is there anybody here who can explain if there possibly could exist a corresponding link between earlobe shape and bodily figure (apart from the mere fact that attached earlobes are a recessive genetic trait, of course)?--Hildeoc (talk) 09:30, 3 August 2020 (UTC)[reply]

I've never heard of such an association, and the first person who came to my mind with attached earlobes (an old acquaintance of mine) is chubby bordering on obese. 2601:648:8202:96B0:0:0:0:5B74 (talk) 09:53, 3 August 2020 (UTC)[reply]

Earlobes are either attached to the side of the head, or detached and only connected to the ear itself. Yes, free earlobes are the dominant trait while attached earlobes are the recessive trait. Researchers have looked at 34 genetic markers that influence earlobe type. This gives references. 84.209.119.241 (talk) 13:05, 3 August 2020 (UTC)[reply]

All of them are "attached". I've never seen one yet that was floating in space. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:44, 3 August 2020 (UTC)[reply]

^{See V.vGogh. 84.209.119.241 (talk) 20:36, 3 August 2020 (UTC)}[reply]

Unfortunately, Van Gogh didn't have Jesus around. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:27, 3 August 2020 (UTC)[reply]

More like van Gagh 93.136.213.247 (talk) 21:46, 4 August 2020 (UTC)[reply]

You've never seen an astronaut's earlobes, then? --47.146.63.87 (talk) 21:48, 3 August 2020 (UTC)[reply]

Working through some older edit requests, but I don't know what to make of this one at Talk:Lean (drug)#Semi-protected edit request on 21 July 2020. The article states that promethazine induces CYP2D6, which doesn't seem to be true ([1]). As I understand it, CYP2D6 turns codeine into morphine. So does promethazine inhibit CYP2D6, meaning that less CYP2D6 can metabolize codeine, so there's more of that in the bloodstream, making people feel more high? But I thought morphine makes people feel high? I would appreciate it if someone can also take care of the edit request, but I've been thinking about this one for a while that I need to know the answer too. This is not what I studied in college! ◢  Ganbaruby!  (Say hi!) 13:49, 3 August 2020 (UTC)[reply]

Codeine is itself inactive; it's a prodrug. It's converted by the liver (by the CYP2D6 enzymes in liver cells) into morphine, which is of course active. This conversion happens slowly, which makes the effects of codeine different from those of directly administering morphine. And co-administration of drugs (in this case promethazine) often means they interact with each other, which can lead to different effects from when the drugs are administered by themselves. If promethazine inhibits the activation of codeine, that generally means the blood concentration of the active drug will be lower. It also often means the duration of effect will be longer, since the body is metabolizing the drug ("clearing it out") more slowly. --47.146.63.87 (talk) 21:46, 3 August 2020 (UTC)[reply]

That's what I would like to know. What happens if you boil such foods for half an hour. AboutFace 22 (talk) 00:31, 4 August 2020 (UTC)[reply]

Protein denaturing for one. Sagittarian Milky Way (talk) 00:45, 4 August 2020 (UTC)[reply]

In the traditional recipe for carbonade flamande (a beef stew), tough, dry, and sinewy cuts of meat such as foreshank are simmered for hours (see Simmering#Dutch and Flemish cuisine). This denatures specifically the elastin and collagen that bundle the muscle fibres together, so that the cooked meat can easily be separated into threads. If you boil such meat at a higher temperature, other proteins form clumps as they denature, making the meat even tougher. Something similar is true for fibrous root vegetables and many kinds of beans. Simmering breaks down the pectin (not a protein), making the cell walls leaky and thereby the veggies soft, up to mushy. Adding a bit of baking soda to the water speeds up the process.  --Lambiam 09:21, 4 August 2020 (UTC)[reply]

Thank you @Lambiam. A helpful answer. AboutFace 22 (talk) 00:41, 5 August 2020 (UTC)[reply]

@Graeme Bartlett: would [2] or [3] be more useful for polymer feedstock? EllenCT (talk) 03:17, 4 August 2020 (UTC)[reply]

Both of these articles are making carbonate salts, first one is making sodium carbonate, and the second, I don't know, but would be a carbonate too. Inorganic carbonates are not useful for making polymers. To make polymer feedstocks, the carbonate needs to be reduced. Perhaps to methanol, ethylene glycol, ethylene or vinyl chloride. So it may have to have some electrolysis going on. Have you checked out our article on carbonic anhydrase? It is speeding up conversion of carbon dioxide to bicarbonate ions. Graeme Bartlett (talk) 06:19, 4 August 2020 (UTC)[reply]

One suggested technique for reducing the impact of global warming is dumping alkali in the sea to trap dissolved carbon dioxide as carbonate rocks. But quite simply crude oil is such a good source for polymer feedstock nothing else is ever going to compete. What we really need to do to stop global warming is stop using fossil fuels to power cars and trucks and ships and electricity: polymer production is such a minimal use of fossil fuels (and so much of it ends up staying as a plastic long-term anyway and not turning into carbon dioxide) it's not a major problem. Wind farms and solar panels are what we need right now. Blythwood (talk) 20:23, 5 August 2020 (UTC)[reply]

Indeed! I am back from abiotic to ocean GMO microbial solutions for the emergency case at present, but some of those abiotic reactors which also desalinate look amazing. EllenCT (talk) 21:01, 5 August 2020 (UTC)[reply]

@Graeme Bartlett: thank you for pointing out the carbonic anhydrase article. I have found more reviews.[4][5]. This is such an exciting area! Please have a look at [6] and [7]. EllenCT (talk) 00:19, 6 August 2020 (UTC)[reply]

Please remember that catalysts don't make possible any impossible reaction but they can only speed up a possible one, and this only in the direction that is currently energetically favorable. That is, if the PH is wrong you cannot obtain any bicarbonate ions from CO2 and water, but instead the catalyst will accelerate the conversion of bicarbonate ions to CO2 and water. But even if you can produce thousands of tons of the enzyme and store billions of tons of water containing your bicarbonate ions after separating them from the catalyst, they are not stable and will quickly free all CO2 again if they are not bound with alkali AND then kept in a cool and basic environment. So I cannot take seriously such claims as in your second link ".. a hybrid system which contain[s] all these CO2 capturing agents will surely prove to be key to mitigate climate change". They didn't name any capturing agent for CO2 in the abstract and CA is surely not one. 2003:F5:6F0C:E600:487C:DA02:59F5:AE62 (talk) 20:49, 8 August 2020 (UTC) Marco PB[reply]

is cradle cap the same thing as seberrhoeic dermatitis? If you have cradle cap as baby does that mean it will stay with you lifelong does it become seberrhoic dermatitis? — Preceding unsigned comment added by 203.219.66.131 (talk) 12:28, 4 August 2020 (UTC)[reply]

It is seborrhoeic dermatitis some of the time: see article cradle cap. It says babies usually get over it in a few months, but sometimes it persists til age 2-3 years. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 14:07, 4 August 2020 (UTC)[reply]

Asked by Willy turner (talk) 13:30, 4 August 2020 (UTC)[reply]

It's the high voltage that fires the spark plug. --Guy Macon (talk) 14:20, 4 August 2020 (UTC)[reply]

You can get resistor spark plugs that "incorporates a ceramic resistor to suppress ignition noise generated during sparking". Alansplodge (talk) 14:34, 4 August 2020 (UTC)[reply]

Or get something even quieter? Martinevans123 (talk)

Or for slightly more noise an appropriate grass eating animal is more environmentally friendly. _{may not be allowed in all locations} Sagittarian Milky Way (talk) 19:52, 4 August 2020 (UTC)[reply]

The lawn in question may be a neighbour's.  --Lambiam 19:57, 4 August 2020 (UTC)[reply]

... and not necessarily: "Holy cow!" (Batman) Martinevans123 (talk) 19:59, 4 August 2020 (UTC)[reply]

There are also electric and hand lawnmowers, though at least with some hand mowers you have to collect the clippings. And of course an electric motor still has the potential for producing interference, though motors tend to be better-shielded and also don't usually produce the characteristic "bursts" of EMF like spark plugs. They're also better for everyone's health as virtually all gasoline mowers use two-stroke engines which produce lots of nasty pollution. --47.146.63.87 (talk) 21:42, 4 August 2020 (UTC)[reply]

That might be true in the US, but in the UK most non-electric mowers use four-stroke engines, which are a lot less polluting, and quieter. PaleCloudedWhite (talk) 22:30, 4 August 2020 (UTC)[reply]

Ah, didn't know that! Very good! --47.146.63.87 (talk) 00:40, 5 August 2020 (UTC)[reply]

We Brits tend to live a lot closer to each other. Alansplodge (talk) 19:43, 7 August 2020 (UTC)[reply]

To expand on the sciency stuff a bit: a moving electrical charge produces electromagnetic radiation. This can be modeled as waves in the electromagnetic field, and when two waves overlap they interfere with each other. You're presumably watching over-the-air TV, which is also transmitted by electromagnetic waves, and it just so happens that the waves produced by the spark plugs overlap in frequencies with those being used for the TV transmission, producing electromagnetic interference. Another commonplace example of such interference is from microwave ovens. They use microwaves in the 2.4 GHz band. The ovens work by trapping the microwaves inside, but no real oven is perfect and so some microwaves "leak". Because of this, this frequency band is not feasible to restrict usage of to licensed users, but this also means the band is used by many consumer wireless technologies, such as Wi-Fi. Thus, use of a microwave oven can cause interference with these. --47.146.63.87 (talk) 21:42, 4 August 2020 (UTC)[reply]

for an aeroplane, instead of using spoilers, can landing upside down be used, to reduce runway length requirement? assuming landing gear is available on the up side as well. thanks! — Preceding unsigned comment added by 117.219.197.124 (talk) 20:08, 4 August 2020 (UTC)[reply]

What is your theory behind the claim that an upside-down plane would require less runway? --Guy Macon (talk) 21:03, 4 August 2020 (UTC)[reply]

my theory is that lift will be applied downwards by the wings. like done by spoilers.

Why not just have the wings mechanically change shape? You could perhaps utilise technology similar to the flap? That might be preferable to having to flip a plane upside down during landing. Zindor (talk) 01:03, 5 August 2020 (UTC)[reply]

The obvious problem with the proposal is that the plane still requires lift to keep from crashing into the ground until the moment the wheels are supported. Therefore it requires the plane to instantaneously turn upside-down when the wheels touch down. --174.89.49.204 (talk) 01:10, 5 August 2020 (UTC)[reply]

Thrust reversers, which are increasingly used on large aircraft, do something sort of similar but rather more practical. Instead of reorienting the whole craft, they just "point" the engine thrust forwards. --47.146.63.87 (talk) 02:52, 5 August 2020 (UTC)[reply]

The sentence "my theory is that lift will be applied downwards by the wings. like done by spoilers." shows where the OP's thinking went astray. There is nothing magical about reducing lift that reduces runway length requirement, Spoiler (aeronautics) explains that when spoilers are deployed on landing they greatly reduce lift (desirable for other reasons but doesn't slow down the plane) and increase drag (which does help the plane to stop quicker). Landing upside down would not increase drag. It also would not decrease lift! You would still have to orient the plane so that it touches down gently instead of smashing the plane on the pavement. If you don't care how hard you hit, you can reduce the runway length required to zero by flying straight down at maximum speed. There have been zero complaints from anyone who has tried this, but the airports don't like having to collect the scrap metal and then fill in the crater. --Guy Macon (talk) 09:05, 5 August 2020 (UTC)[reply]

how about aircraft carriers? would landing upside down be of any use there? — Preceding unsigned comment added by 117.251.237.158 (talk) 11:51, 5 August 2020 (UTC)[reply]

Same problems as noted by Guy Macon, except this time it is harder to repair a ship under way at sea. --Jayron32 12:27, 5 August 2020 (UTC)[reply]

Just use a Tailhook, as with landing on an aircraft carrier or an airport equipped for it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:48, 5 August 2020 (UTC)[reply]

thanks! — Preceding unsigned comment added by 117.246.93.181 (talk) 14:51, 5 August 2020 (UTC)[reply]

You may be interested in the flexible deck system, where aircraft were landed wheels-up on a carrier deck covered with layers of inflated fire hoses. Seemed like a good idea at the time. Alansplodge (talk) 17:53, 5 August 2020 (UTC)[reply]

Craig Hosking landed a modified Pitts S2 upside down http://www.hoskingaviation.com/airplaneAction.html There are vids on youtube too TrogWoolley (talk) 22:49, 5 August 2020 (UTC)[reply]

Just so you know, Flight was not a documentary :-). Which brings up another sense of "spoilers", I suppose. --Trovatore (talk) 18:33, 6 August 2020 (UTC) [reply]

Is there a place where I can find water's specific heat capacity for different temperatures, let's say 30-100°C? I'm thinking that if a body of a specific temperature is covered with warmer water, there will be some water temperature at which heating thru conduction is exactly balanced by cooling thru vaporization. 93.136.213.247 (talk) 21:58, 4 August 2020 (UTC)[reply]

You may find the article on Thermal conductivity useful. It doesn't have the specific heat capacity of water at different temperatures, but it talks about other factors involved in heat transfer Zindor (talk) 22:42, 4 August 2020 (UTC)[reply]

The NIST page for water has a graph with those heat capacities. --OuroborosCobra (talk) 14:38, 5 August 2020 (UTC)[reply]

Thanks, even better it has an approximation formula! Unfortunately I've realized I need to take into account other factors like water vapor pressure so I don't think I'll get a neat equation in which I can plug numbers and solve. 93.136.199.101 (talk) 19:39, 5 August 2020 (UTC)[reply]

You'd probably get all the data you need from a set of steam tables. I can't point you at one in particular, google gives you many choices. Greglocock (talk) 20:57, 5 August 2020 (UTC)[reply]

Obviously, it's very important and healthy to brush teeth twice a day (or after meals), But my question is about importance. Which of these two is more important, if you have only one of them to choose? (before going to sleep or after waking up) --ThePupil (talk) 06:09, 6 August 2020 (UTC)[reply]

Brushing your tooth immediately after each meal (which some people do as if it is a religious duty) is overkill; the natural production of saliva will wash away most of the stuff the bacteria causing caries thrive on, as well as most of these bacteria when they start multiplying (which they can do very rapidly). I don't know if this has been the subject of any scientific studies, but I'd think that if your mouth and teeth are meticulously cleaned before bedtime, there is not much left for the bad bacteria as a growth medium. However, they do not need much, and at night saliva production slows down significantly, so just a little amount of carbohydrates (not just sugar!) can already give rise to a significant layer of dental plaque, which is why brushing in the morning is important: if left the plaque will eventually harden into calculus, which can no longer be brushed or flossed away. So I expect the verdict to depend on the meticulosity of the pre-bedtime cleaning of one's mouth and teeth, which is hard to control in a scientific study. If this pre-bedtime cleaning is an (even mildly) sloppy job, then brushing and flossing in the morning may give the better result. But if thoroughly done before going to bed, pre-bedtime cleaning may work out better.  --Lambiam 07:33, 6 August 2020 (UTC)[reply]

Do what your dentist tells you, not what anonymous persons on the internet tell you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:15, 6 August 2020 (UTC)[reply]

I am with Baseball Bugs on this. I also note that the above comment is a perfect example of the right way to deal with medical questions and answers on the reference desks; no attempts to make up new rules of control other people, just good, sound "do what your dentist tells you" medical advice.

There is a dentist who writes the following on the Mayo Clinic website:

"The American Dental Association recommends brushing your teeth twice a day with fluoride toothpaste for two minutes each time... In choosing when to brush your teeth, you might also consider your diet. If you've eaten an acidic food or drink, avoid brushing your teeth right away. These acids weaken tooth enamel, and brushing too soon can remove enamel.

Besides brushing your teeth, to keep your mouth healthy, do the following:

• Floss daily.
• Use mouthwash after brushing and flossing.
• Drink plenty of water.
• Eat a healthy diet and limit sugary food and drinks.
• Avoid frequent snacking.
• Replace your toothbrush every three to four months, or sooner if the bristles are irregular or splayed.
• Schedule regular dental checkups with X-rays and cleanings."[8]

Needless to say, while the expert advice of a dentist on the Mayo Clinic webpage is better than the advice of a random person on the internet, the advice of an actual dentist who is looking at your actual teeth is even better. --Guy Macon (talk) 12:08, 6 August 2020 (UTC)[reply]

For those looking for academic research on the topic, this might be of use:[9] -Guy Macon (talk) 12:14, 6 August 2020 (UTC)[reply]

That study is only about oral hygienic behaviour and does not relate it to dental health.  --Lambiam 14:09, 6 August 2020 (UTC)[reply]

The very first sentence of the question ("Obviously, it's very important and healthy to brush teeth twice a day (or after meals).") makes it clear, IMO, that the questioner is not seeking advice but is posing a hypothetical scientific question, which I attempted to treat as such.  --Lambiam 14:09, 6 August 2020 (UTC)[reply]

And, the best source for information from that hypothetical scientific question is to ask their dentist. --Jayron32 18:31, 6 August 2020 (UTC)[reply]

@Lambian, thank you for your comment, I think you understood me properly. I looked for scientific support and explanation rather than for medical advice. I want to support the answer based on scientific source and logically explained (something that many dentist can't do, unfortunately), I can't refer by "my lovely dentist said to do so". I have a sense and I want to use it and get explanations if I have the possibility to understand it. Not looking for medical advice here, not only now but never.--ThePupil (talk) 00:00, 7 August 2020 (UTC)[reply]

Sagittarian Milky Way (talk) 17:47, 6 August 2020 (UTC)[reply]

Can you rephrase the question? It's confusingly worded.--Jayron32 18:29, 6 August 2020 (UTC)[reply]

Do the serrations of leaf edges increase the plant's Darwinian fitness even if they're not stiff and sharp enough to scratch human skin? Sagittarian Milky Way (talk) 19:19, 6 August 2020 (UTC)[reply]

Quora - What's the evolutionary advantage of serrated leaves vs. smooth edged leaves?: "Some researchers have hypothesized that serrated (or toothed) leaves allow for earlier (spring) photosynthesis in their growing season in temperate forests, thus giving them more time for photosynthesis before fall and winter sets in. This could be one way for certain plants to be able to gain some evolutionary advantage in temperate conditions". Alansplodge (talk) 19:22, 6 August 2020 (UTC)[reply]

The Wikipedia article titled Serration also contains other likely advantages they provide. --Jayron32 19:24, 6 August 2020 (UTC)[reply]

And a lot of things other than humans might want to do things to plants. Many plant defenses against herbivory are targeted at small mammals or arthropods. Among these: caffeine and nicotine, which poison insects and can even be used as pesticides. In fact a whole class of manmade pesticides, the neonicotinoids, are based on nicotine's structure. --47.146.63.87 (talk) 20:55, 6 August 2020 (UTC)[reply]

These cockroach-like beetles have recently popped up at night in a living room, Warsaw, Poland. The length is about 2 cm, prefer to crawl or sitting still, but when disturbed they fly away. What's the species? Thanks in advance. Brandmeister^talk 22:23, 6 August 2020 (UTC)[reply]

The pictures aren't clear, but they rather remind me of certain types of Ground beetle. But most of those don't fly, so that may be a mistake. Iapetus (talk) 09:30, 7 August 2020 (UTC)[reply]

In the pictures I see rather something like a Common furniture beetle, a Red flour beetle or a Firefly. And I would say that Cockroaches look rather different: they have four transparent wings while your insect seems to have elytra, the hardened forewings of true beetles (Coleoptera). 2003:F5:6F0C:E600:487C:DA02:59F5:AE62 (talk) 21:06, 8 August 2020 (UTC) Marco PB[reply]

Sagittarian Milky Way (talk) 01:03, 7 August 2020 (UTC)[reply]

No doubt a multitude of things, maybe even wind from outside shaking some parts. You've ventured out of the realm of en-wiki with this question. Maybe look up Y!A. Zindor (talk) 03:42, 7 August 2020 (UTC)[reply]

Many of those fans have one-way slats on the outside that are designed to ensure that air can flow out but not in. On a windy day these can flap about.--Shantavira|^{feed me} 09:54, 7 August 2020 (UTC)[reply]

Example: SN 1987A neutrinos famously reached observers several hours before the visible light arrived, over a distance of 170,000 LY. That's because they made their way through the supernova mass without obstruction, while the light took longer to make its way through. But, what about special relativity? Would they experience mass dilation? Various figured like 0.3 eV are given for the neutrino mass but it's not clear whether that's a rest mass (if neutrinos even have that), or that neutrinos are always travelling at lightspeed and that's their relativistic mass. Thanks. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 03:00, 7 August 2020 (UTC

If one were to assume that neutrinos travel at the speed of light, then i can see only two possibilities: either the special relativity theory needs updating, or neutrinos possess infinite energy. The Measurements of neutrino speed article might contain the answer you are after, and is more reliable than my ramblings. Zindor (talk) 04:02, 7 August 2020 (UTC)[reply]

If they do have mass, it is very small, and they have a highly relativistic speed. Almost all their energy/mass is due to that mass dilation. You can consider refractive index as something that slows down light. I do not know if there is an equivalent thing for neutrinos, however they do have a very small interaction with normal matter by way of the weak force. Graeme Bartlett (talk) 04:11, 7 August 2020 (UTC)[reply]

Thanks all. Measurements of neutrino speed was very helpful. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 09:12, 7 August 2020 (UTC)[reply]

A lot of a supernova's light is produced by radioactive decay of stuff in the expanding cloud of ejecta, and that decay of course doesn't happen instantly. Off the top of my head I don't know the relative contributions of different things; you'll have to dig into some sources if you want precise numbers. The neutrinos, by contrast, are all produced in the initial core collapse, and actually are what most of the energy released in a supernova goes into. --47.146.63.87 (talk) 23:39, 8 August 2020 (UTC)[reply]

Is there a good book about the development of modern chemical nomenclature? —Tamfang (talk) 05:33, 7 August 2020 (UTC)[reply]

Any particular area of chemistry (chemical elements, organic structures, generic drug names, salts, strong acids, environmental substances, etc.)? DMacks (talk) 06:58, 7 August 2020 (UTC)[reply]

Like who came up with –ane and –ene and –yne, and when? —Tamfang (talk) 05:53, 8 August 2020 (UTC)[reply]

Wouldn't that be the "Gold" Book, or IUPAC Compendium of Chemical Terminology, which is almost surely lying around in one of your nearby labs or classrooms or libraries? Pretty much every single item contains either a source, a reference to another color book, or an original research citation. The book is also available in PDF form at zero cost: but the really serious scientist probably wants to buy a copy. (sic). That's probably as close to a compendium dictionary of chemical etymology as you'll find... there are plenty of in-book citations to previous papers and conferences and older publications that itemize the development of individual terms. Nimur (talk) 17:37, 7 August 2020 (UTC)[reply]

Oooh, a few excerpts I found exciting, extracted from the page on the lore of the Gold Book (which provides some fascinating meta-historiography on the topic of the development of the documentation of the documentation):

"The impact of the Gold Book on society is difficult to measure due to a lack of information of usage of the Gold Book website prior to 2017... Data obtained for Wikipedia events (edits to pages where a DOI was added – all languages), indicates that Gold Book DOIs (each entry has a DOI) have been added for 1952 entries (~30% of current entries) as well as the overall Gold Book being referenced 2485 times... Looking deeper these entries are referenced in 7581 Wikipedia pages across 84 countries."

Dear colleagues, ... today I can say I am proud of our efforts.

Nimur (talk) 17:44, 7 August 2020 (UTC)[reply]

A quick glance at that book did not turn up any etymology. —Tamfang (talk) 05:53, 8 August 2020 (UTC)[reply]

Don't forget to consult our sister project Wiktionary wikt:-ane, wikt:-ene, wikt:-yne. Some of us try to add chemistry words there. The when aspect is missing from these however. Graeme Bartlett (talk) 06:24, 8 August 2020 (UTC)[reply]

I understand that both with Direct current (as electrical current from a battery to a receiving device) and with Alternating current (electrical current from a current manufacturing device to a receiving device in a closed electrical orbit or "circuit") there is always a need to create more electrical current to have the receiving device working because electrical current is used until it gets over and new current is needed.

Why does Direct current disntincted from Alternating current?
I mean, is this distinction more than a mere physical observation in the sense that it gives some practical benefit?

Big thanks; 182.232.41.11 (talk) 07:01, 7 August 2020 (UTC)[reply]

Big advantages of direct current:

• Most electronics uses DC. AC has to be converted to DC to power a computer or cell phone.
• You can get DC out of a battery.

Big advantages of alternating current:

• You can easily convert it to a higher or lower voltage with a transformer.
• By using transformers, you can send it over long distances.

That last one is why your house has AC. If it was DC they would have to make a bunch of small power plants so that one is close to your house. --Guy Macon (talk) 18:04, 7 August 2020 (UTC)[reply]

• Formerly, DC had one more big advantage: for large motors like the ones in electric trains, AC motors used to be less efficient. I think it was around 1975 that this changed; anyway, this is the reason why many rail systems built before that era, such as older subways, were built to use DC; and since changing everything at once to use AC would be complicated and expensive, generally they still do. --174.89.49.204 (talk) 23:23, 7 August 2020 (UTC)[reply]

Not just older subway system; railway systems all over Europe began electrification before 1950 and used either DC or low frequency AC, which allows the same simple yet efficient motors as the DC system, but also allows high voltage for transmission. The downside is that it needs a heavier on-board transformer. Some railway systems decided to switch later, leading to mixed systems. But new metro/subway systems tend to use DC too. This is because DC has another advantage not yet mentioned: it doesn't suffer from the skin effect. If limited clearance doesn't allow high voltage (tens of kilovolts), you're stuck with low voltage (hundreds of volts) and high currents (kiloamps) that need big conductors. In big conductors, the skin affect causes AC to have higher resistance than DC. PiusImpavidus (talk) 09:30, 8 August 2020 (UTC)[reply]

Thanks, I did not know about that as a difference. (As to "not just", I did say "such as".) --174.89.49.204 (talk) 23:32, 8 August 2020 (UTC)[reply]

Is this why elevated subways have so many little buildings where the electricity comes in? If it's DC that is. 600 to 660 Volts DC for New York City, don't remember exact number. There's small windowless buildings with lots of conduits between tracks and street canyon wall. Usually not at stations. Underground ones must exist too but would be hard to distinguish from doors to emergency exits etc. Sagittarian Milky Way (talk) 22:27, 7 August 2020 (UTC)[reply]

I don't know about the specific buildings you refer to, but probably the answer is yes. A subway or similar line using 600 volts DC requires electrical substations at regular intervals to supply the power. The normal pattern would be to supply AC at a higher voltage to the substations, and each one would rectify it to DC (using a method that depends on the age of the substation) as well as transforming the voltage down. --174.89.49.204 (talk) 23:20, 7 August 2020 (UTC)[reply]

Those windowless buildings could be either feeder stations, providing DC electricity to the power rail, or cabinets containing the relays that control signals and points (switches). The former should have big cables connecting them to the power rail and the running rails (used for return current), the latter, which should be more common, may have cables connecting them to the running rails (for track circuit train detection). I've never personally observed the elevated railway systems of American cities. PiusImpavidus (talk) 09:30, 8 August 2020 (UTC)[reply]

Hence the War of the currents. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:19, 7 August 2020 (UTC)[reply]

My complement for your great answer, dear Guy Macon. 182.232.41.11 (talk) 00:34, 8 August 2020 (UTC)[reply]

On a slightly different topic, that lack of skin effect, as well as other advantages, actually means if you get up to really high voltages, DC can be more efficient than AC over long distances, which is why HVDC has been growing in popularity as solid-state power electronics have advanced. But again, that's for long-distance transmission links. --47.146.63.87 (talk) 23:46, 8 August 2020 (UTC)[reply]

I’m trying to understand how load paths work. If a single beam can take a point load, does that mean any other beams connected to it through shear connections can also take the point load? Or can something else in the system fail (for example one of the shear connections or another beam in the system) if they have a lower load capacity than the one with the point load. 90.194.50.247 (talk) 10:48, 7 August 2020 (UTC)[reply]

I myself know very little about Structural mechanics, but from spending several years in an office literally sitting next to structural engineers whose main jobs were designing lattice towers, and checking the structural integrity of existing towers after proposed and actual modifications and load additions by others, I can tell you this: it's a difficult topic and you are unlikely to get information useful to you by asking questions from a forum such as this. You need to listen to and read, and understand, qualified instruction and formal texts on the subject. This matters, because failures in structures due to poor/uninformed design (or build) can and do kill people. {The poster formerly known as 87.81.230.195} 2.217.210.84 (talk) 08:22, 9 August 2020 (UTC)[reply]

How are old movies released in HD? Is there much of a difference between SD and Hd with old movies? 90.194.50.247 (talk) 19:00, 7 August 2020 (UTC)[reply]

They typically use an upscaler and sometimes clean up visual artifacts. Killiondude (talk) 19:18, 7 August 2020 (UTC)[reply]

What's the pixel analog of analog film film anyway? VHS is probably lower-quality upscaling source. Sagittarian Milky Way (talk) 21:55, 7 August 2020 (UTC)[reply]

I don't think they would be producing HD disks from standard VHS tapes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:05, 7 August 2020 (UTC)[reply]

35mm film apparently has a "resolution" comparable to 4K or 6K (under ideal circumstances; also, the copying process to create release prints was not lossless). Cheers ⌘ _hugarheimur 09:27, 8 August 2020 (UTC)[reply]

Oftentimes, old movies were recorded on film, and that film actually has a high enough resolution (not in a digital sense, but in terms of detail, yes) that, if rescanned from the original film, it can be digitized to HD quality. TV shows, on the other hand, were often recorded on tape rather than film. Tape didn't have that same level of "resolution," and so you need an upscaler for old TV shows, and any movies recorded on tape instead of film. --OuroborosCobra (talk) 02:40, 8 August 2020 (UTC)[reply]

To be a bit more specific, all old movies were recorded on film, because that was all there was. Usually it was 35 mm film, which as noted above is about as good as HD. TV shows in the early days were not recorded at all, or were recorded on tape, but 35 mm film eventually became standard after one influential show began doing it: See I Love Lucy#Production. --174.89.49.204 (talk) 05:52, 10 August 2020 (UTC)[reply]

I saw many times videos of people cooking (or baking?) pork in a fire pit by putting the pork inside and sealing this pit tightly (usually by mud) and keep it inside for long time. Do these pits have a way to 'breathe'? any fire needs oxygen, isn't it? Otherwise I really don't understand scientifically how those fire pits works.--ThePupil (talk) 23:06, 7 August 2020 (UTC)[reply]

Fire pit might have some answers. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:33, 7 August 2020 (UTC)[reply]

Just by the way, you mean breathe, not breath. </peeve> --Trovatore (talk) 23:46, 7 August 2020 (UTC) [reply]

Thank you. I edited it. I appreciate your note. Who knows how many times I did this mistake and how many times I'd do it unless you noted it. Thank you.--ThePupil (talk) 00:05, 8 August 2020 (UTC) [reply]

My guess is that you saw a video of Kālua pork being made. The thing is that it's not really a fire pit. It's not open flame that's cooking the pork; the fire is meant to heat up the stones and vegetation and earth that's doing the cooking...more of an oven than an open-flame kind of deal. You'll want to read earth oven for more details. bibliomaniac15 00:06, 8 August 2020 (UTC)[reply]

From the article on the photoelectric effect, the implication seems to be that electrons are simply "knocked loose" and hence the flow of electricity. But what if the cell and all of its connected components were instead (mostly) devoid of electrons, say in deep space. Would the positively charged assemblage thereof be able to be powered up by a ray of sunlight, or would it simply remain "dead" until enough free electrons floating about in the vacuum of space had been "captured"? In other words, can electrons be created by the photoelectric effect? Earl of Arundel (talk) 06:42, 8 August 2020 (UTC)[reply]

Why do you think that objects in deep space are (mostly) devoid of electrons? Why do you think that the photoelectric effect involves capturing electrons from the environment? --Guy Macon (talk) 07:03, 8 August 2020 (UTC)[reply]

It was more of a spherical cow kind of question. Assuming those conditions were met, would the photoelectric effect in fact still occur? Earl of Arundel (talk) 07:30, 8 August 2020 (UTC)[reply]

Spherical cows are simplifications. You are essentially asking "if a cow was made entirely of bad science fiction stories posted on Facebook. would it still Moo?" You would no longer be talking about a cow, spherical or otherwise. Likewise, your question is no longer talking about the photoelectric effect. --Guy Macon (talk) 16:22, 8 August 2020 (UTC)[reply]

The direct answer to your question is that if a solar cell were "(mostly) devoid of electrons", it would instantly explode with unfathomable violence. It might be instructive to try to calculate the amount of energy required to bring that much positive charge all together in a small space. --Trovatore (talk) 07:08, 8 August 2020 (UTC)[reply]

Well it can't be totally impossible. There are things like alpha particles "out in the wild". Earl of Arundel (talk) 07:30, 8 August 2020 (UTC)[reply]

An alpha particle can be held together without electrons by the nuclear force, but that only works for things the size of an atomic nucleus. When dealing with something larger than a nucleus (or just a very large nucleus), it no longer works and the thing desintegrates. Without electrons, there would be no photoelectric effect, but neither would there be any structures larger than an atomic nucleus, so no solar panels. PiusImpavidus (talk) 09:56, 8 August 2020 (UTC)[reply]

Disintegrates is a rather mild word. Larry Niven created the notion of the "Slaver digging tool", which "suppressed the charge on the electron". From his description of the effects, I can only conclude that either Niven never actually did the calculation, or he meant it to be a partial suppression. --Trovatore (talk) 17:44, 8 August 2020 (UTC) [reply]

Scientists at the Lawrence Livermore National Laboratory were in fact able to remove 100% of the electrons from at least a few uranium nuclei.[[10]] So an atom stripped of its electrons isn't (necessarily) inherently unstable. Granted, given the number of free electrons available here on Earth, such a substance must be highly reactive. Earl of Arundel (talk) 00:25, 10 August 2020 (UTC)[reply]

I guess my real question here is whether or not electrons can be created from photons? Earl of Arundel (talk) 07:30, 8 August 2020 (UTC)[reply]

Two photons together can be converted into an electron and a positron. It's called pair production and has nothing to do with the photoelectric effect. PiusImpavidus (talk) 09:56, 8 August 2020 (UTC)[reply]

Right, and even if this were to occur in a solar cell the net charge would remain zero so... Earl of Arundel (talk) 00:25, 10 August 2020 (UTC)[reply]

A solar cell and connected components consisting of antimatter, say floating in deep space, could be mostly devoid of electrons.  --Lambiam 12:11, 8 August 2020 (UTC)[reply]

Replacing all electrons with positrons, all protons with antiprotons etc. is not what most people think of when they say "take away all of the electrons". --Guy Macon (talk) 16:22, 8 August 2020 (UTC)[reply]

Who mentioned or suggested "taking away" the electrons? The hypothetical question implied their absence, but not the why or how of that absence.  --Lambiam 22:22, 8 August 2020 (UTC)[reply]

Sigh... See Paraphrase. Replacing all electrons with positrons, all protons with antiprotons etc. is not what most people think of when they say "(mostly) devoid of electrons". Happy now? --Guy Macon (talk) 22:40, 8 August 2020 (UTC)[reply]

Very few people would say that, and if they do, I can only guess what they were thinking of.
Anyway, it was meant as a joke, which is why I put it in a smaller font.  --Lambiam 07:44, 9 August 2020 (UTC)[reply]

In fluid dynamics fluids are treated as continua, with assuming kinetic energy of a piece of a fluid stream as if it were a solid body, while in reality every molecule has its own velocity and, consequently, its own kinetic energy. For example, for a stream of propellant, being expelled from a rocket, we can calculate its kinetic energy given the flow rate and the thrust exerted. Would we assume the propellant stream to be a small set of uninteracting particles (molecules) we should come to the conclusion, that given momentum of the propellant may be consistent with multiple values of kinetic energy. As far as I remember, it is explained in statistical mechanics, that in a big enough set of interacting particles distribution of kinetic energies of the particles is such, that the sum of their components parallel to the direction of common motion tends to the kinetic energy of a continuous body. But I have difficulty with finding the exact theorem or equation in literature. Couldn't somebody give me a reference to an article (or articles) in Wikipedia, where this principle is explained and/or relevant sources are cited? Эйхер (talk) 14:54, 8 August 2020 (UTC)[reply]

Courtesy links: Our Continuum hypothesis article is for the mathematical hypothesis about the possible sizes of infinite sets, but it does contain the hatnote: "For the assumption in fluid mechanics, see Continuum assumption", that link being a redirect to the relevant portion of Fluid mechanics#Assumptions (which refers to it as both the "continuum assumption" and the "continuum hypothesis"). We also have Continuum mechanics and Aerodynamics#Continuum assumption. Also relevant are Knudsen number and Compressible flow#Introductory concepts. -- ToE 15:54, 8 August 2020 (UTC) Edited to reflect hatnote cleanup; explicitly noted "Courtesy links". -- ToE 22:04, 8 August 2020 (UTC)[reply]

Thank You anyway! Here the concept is described, as well as boundaries of its applicability, but not the explanation. What I'm looking for is the theoretical explanation of validity of the "continuum assumption". Эйхер (talk) 17:18, 8 August 2020 (UTC)[reply]

Not a physicist but can't help noticing how similar your formulation is to the central limit theorem in mathematics. 93.136.85.102 (talk) 03:58, 9 August 2020 (UTC)[reply]

Suppose you have a black box with a 1 kg mass, moving at a speed of 1 m/s. What is its kinetic energy? Well, 0.5 J, of course. Now you open the box and inside you find a bunch of very active frogs jumping in all directions. Their kinetic energies, added up, are considerable, but do not contribute to the kinetic energy of the box. Now consider a volume of the fluid or gas enclosed in a thin membrane that moves along with the flow at the average velocity of the particles. This forms a virtual box that can be analyzed like the moving box with frogs. A difference is that the membrane is not impermeable, but on the grand scale of things the relatively few particles that enter the virtual box in one direction (passing through the membrane) are compensated by those that exit it in the same direction. So calculations treating this as a homogeneous mass will come out the same as those treating it as particulate.  --Lambiam 07:36, 9 August 2020 (UTC)[reply]

Possibly out of scope, but the concept of stress-energy tensor deals nicely with boxes of frogs, and indeed other less interesting situations such as ideal fluids. HTH, Robinh (talk) 21:34, 9 August 2020 (UTC)[reply]