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August 26

Plants that prefer rainwater, DI water, and acid rain.

So most plants prefer rainwater, some plants prefer DI water, and some acid rain. What are some examples of plants that prefer DI water? (Besides moss and liverworts.). What are some examples of plants that prefer acidic rain?

Did a Google search on (plants that prefer acid rain) and I only found 1 article that talks about that, but it is dated 1980. It says strawberries and tomatoes thrived better at acid rain, but not carrots. Then, found a random page that lists fruits/vegetables that liked acidic soil, and it happened to list carrots, so that was a quick contradiction I found. 67.165.185.178 (talk) 09:13, 26 August 2021 (UTC).[reply]

most Orchids, Bromeliads, and pitcher plants are quite sensitive to dissolved salts in the water, so as a rule you'd want to water them with reverse-osmosis purified water (either as-is or with tiny amounts of neutral NPK fertilizer added: there are special formulations for orchids). Also, some plants, such as Ericaceae, require acidic soil; so slightly acidic or RO water doesn't hurt. Dr Dima (talk) 16:13, 26 August 2021 (UTC)[reply]

To wit: epiphytic plants mostly rely on fog, rain, and accumulating plant detritus (rather than soil) for their water and nutrients, so need relatively pure water. Plants of acidic bog or blackwater conditions are all adapted to acidic, mostly nutrient-poor soil or substrate conditions. Dr Dima (talk) 16:25, 26 August 2021 (UTC)[reply]

Dr Dima, I read your userpage, do you know, if practicing with your non-dominant hand helps your brain noticeably? For example, doing something softcore like brushing your teeth, to something more hardcore like writing - with your non-dominant hand. I'd rather ask you these questions here than on your talk page. 67.165.185.178 (talk) 01:56, 27 August 2021 (UTC).[reply]

Note that what is termed Acid rain can be significantly more strongly acidic than commonly found, naturally occurring acidic soils and groundwater. {The poster formerly nown as 87.81.230.195} 2.122.179.94 (talk) 22:15, 26 August 2021 (UTC)[reply]

August 27

Why perpetual motion considered as free energy if it clearly depending on gravity?

Hydroelectric energy or solar energy never considered as free energy, but why perpetual motion considered as free energy (generator) if it clearly depending on gravity? Rizosome (talk) 04:00, 27 August 2021 (UTC)[reply]

Don't you think gravity is free? ;) --CiaPan (talk) 04:35, 27 August 2021 (UTC)[reply]

A perpetual motion machine is a machine that does work without an energy source. If it ain't free energy (violating the law of conservation of energy), a "perpetual motion" machine is fake – by definition. --Lambiam 06:51, 27 August 2021 (UTC)[reply]

A perpetual motion machine works in cycles - meaning if some sort of weight falls down during part of the cycle, that is legit, but it has to go back up at a later point. As gravity is a conservative force, this means that the average energy given during a cycle is zero, so no perpetual motion machine can use gravity.

Solar is a different thing. Are drinking birds perpetual motion machines? Tigraan^{Click here for my talk page ("private" contact)} 08:29, 27 August 2021 (UTC)[reply]

Read the second sentence of the article you just linked. --Jayron 32 15:42, 27 August 2021 (UTC)[reply]

I know. I somehow misread the original post as thinking that the use of solar is kosher for a "perpetual motion machine", so that was a rhetorical question to test their definition. After all, a drinking bird is a machine, and it is in motion, and perpetually if the conditions are kept constant; but of course it does not violate the second law. Tigraan^{Click here for my talk page ("private" contact)} 08:39, 31 August 2021 (UTC)[reply]

The Sun generates heat by "burning" hydrogen. The supply of hydrogen will eventually run out, but not for about 5 billion years, so while from a human perspective it is effectively an unlimited source of energy, its not a perpetual motion machine. Solar energy gets its power directly from the sun, and hydro-electricity gets it indirectly (the heat from the sun evaporates water, which condenses, falls as rain, collects in rivers or reservoirs, and flows downhill to turn the turbines in the power station). Because the sun, as stated, is not a perpetual motion machine, things powered by the sun are not perpetual motion machines either. A perpetual motion machine (if it existed, which it doesn't) produces energy by e.g. water flowing downhill, and then uses that energy to move the the water back up hill. But it will always take more energy to move the water back uphill than you can get from it flowing downhill (because you can't create energy from nothing, and some is always wasted due to inefficiencies) - which is why perpetual motion machines are impossible. Iapetus (talk) 08:54, 31 August 2021 (UTC)[reply]

How sensitive can microphones be?

Im interested in ways of detecting insects. Like if an ant walks on a linoleum floor, could a micrphone detect it, now or someday with foreseeable technological advances? What if the ant walked on a "clangy" metal table?Rich (talk) 04:13, 27 August 2021 (UTC)[reply]

Reputedly the noise floor of sensitive microphones is at the point where they are detecting the brownian motion of the air molecules nearby. Follow this up http://www.noiseaddicts.com/2008/07/sensitive-microphone-heartbeat-of-snail-ants/ Greglocock (talk) 06:34, 27 August 2021 (UTC)[reply]

Some spiders living in caves detect their prey by feeling with their legs rock vibrations caused by insects walking. So this level of sensitivity should be possible, I think. --CiaPan (talk) 06:51, 27 August 2021 (UTC)[reply]

Hearing worms move through soil is not even cutting-edge (several species of bird can do it, and 2010-vintage hardware was used in the experiments related to it). DMacks (talk) 17:49, 27 August 2021 (UTC)[reply]

Snakes

There are many magazine articles that snakes never bite human beings unless someone puts foot on it.

So, all poisonous snakes will never attack a human being without provocation? --Marvel Avenger (talk) 05:05, 27 August 2021 (UTC)[reply]

Snakes bite either to subdue prey or to defend themselves. To the best of my knowledge, none of the venomous snakes, extant or recently extinct, prey on humans. Therefore, if a person is bitten, that would be either because the snake perceived a person as a threat ("provocation" as you put it), or as a case of mistaken identity (such as when feeding a captive snake, or having the odor of its food on your hands or clothes). Even when a snake does perceive a person as a threat, it doesn't always inject venom when it bites. It may feint a strike, or it may strike without injecting a venom (a so-called "dry bite") and not waste the venom. A feint or a dry bite is more than a sufficient deterrent in most cases. It will rather likely inject venom if you step on it, though. Dr Dima (talk) 06:15, 27 August 2021 (UTC)[reply]

So, all poisonous snakes will never attack a human being without provocation? YES Rizosome (talk) 06:17, 27 August 2021 (UTC)[reply]

Rhizome, you are trying to elicit a binary (always/never) result from a class of complex and variable real-world situations. The macro-world simply does not work like this – real-world alternatives for nearly all situations are generally more or less probable over a spectrum from "almost always"/"almost never", through "more often"/"less often" to "maybe"/"maybe not", and many if not most situations have three or more different possible outcomes. {The poster formerly known as 87.81.230.195} 2.122.179.94 (talk) 15:43, 27 August 2021 (UTC)[reply]

Don't put your confidence in a magazine article. Almost any animal that can hurt you will attack if it feels strongly threatened and there is no safe retreat. It is true that snakes generally prefer to retreat. A retreat is evidently not possible if you step on one, but the animal being startled may already set off the "fight" branch of the fight-or-flight response. Black mambas are feared for their aggression, and many people who were bitten by one did not step on it or willfully provoked it before the attack. --Lambiam 06:40, 27 August 2021 (UTC)[reply]

Snakes may perceive walking through their habitat as "provocation" so we need to be careful with words because that is not what most English speaking human beings understand that word to mean. The same is true of rattlesnakes if they perceive their babies to be at risk. Cullen³²⁸ Let's discuss it 06:45, 27 August 2021 (UTC)[reply]

And then, though it's not the happiest topic in the world, there are those (thankfully exceedingly rare) cases of a constrictor preying on a human being [1]: bites typically will happen, incident to such an attack [2], but it's one of the few scenarios in which you've been bitten by a snake (and a massive one at that) and yet that is not your biggest problem at the moment... SnowRise ^{let's rap} 10:35, 27 August 2021 (UTC)[reply]

Snakes cannot understand intent. The snake doesn't know if you are or are not trying to harm them. Most snakes will flee as a first line of defense from predators, and if they see you as a threat, they will first try to flee. If they perceive that they cannot flee, because you accidentally step on them, or perhaps come really close to stepping on them, they may reflexively bite you. This is true even if you mean no actual harm. The snake does not know this. Snakes do not seek out humans to bite them, they try to avoid people but may bite if they feel threatened by a human (even if the human doesn't actually intend harm). Some snakes do use threat displays as a means to scare off threats rather than run first, famously Agkistrodon piscivorus, a very common snake in the U.S. known as a "water moccasin" or a "cottonmouth", will often lunge threateningly at people to frighten them, though if the person themselves flees, bites are rare. --Jayron 32 12:05, 27 August 2021 (UTC)[reply]

The rattlesnake is lucky to evolve a rattle that tells you where the tail is, when the snake is hard to see. Not sure how effective that is when the snake is sleeping. Sagittarian Milky Way (talk) 13:51, 27 August 2021 (UTC)[reply]

From what I was taught, in general, snakes (at least my local Aussie ones) do indeed prefer to flee rather than attack a human if (as Jayron rightly notes) the snake perceives that they have that option. That said, there are exceptions. As an Australian, whilst most of our snakes generally avoid attacking humans, the King brown snake (Pseudechis australis) is something of an exception; it has been known to bite even humans who are sleeping. Eliyohub (talk) 07:32, 1 September 2021 (UTC)[reply]

Colorless or colored elemental fluids

What causes nitrogen gas (or hydrogen or oxygen) to be colorless whereas fluorine, chlorine and bromine are colored? Sandbh (talk) 13:15, 27 August 2021 (UTC)[reply]

If the gas appears colored to you, that is because the molecules of the gas have absorption bands in the visible range; which is to say that when light interacts with those molecules, the light of certain wavelengths is absorbed; as a result the remaining light that is passing through the gas no longer is colorless (white light) but now has a color, created by your eyes receiving some wavelengths of light, but not others. All gases, even colorless ones, absorb light, however if they don't absorb sufficiently in the visible spectrum, and instead primarily absorb in the UV or IR ranges, the gas will appear "colorless" because all of the wavelengths of light you can see are still reaching your eyes. --Jayron 32 13:24, 27 August 2021 (UTC)[reply]

And along with most other sighted terrestrial organisms, our eyesight has evolved to see in the part of the electromagnetic spectrum in which most commonly encountered gasses, principally nitrogen, are minimally light-absorbent. Life forms that evolved in a mostly chlorine (or chlorine compound) atmosphere (assuming that to be possible) would likely evolve sight in e-m bands in which chlorine (or its prevelant compound) is non-absorbant but rare gasses like nitrogen and oxygen might appear coloured. {The poster formerly known as 87.81.230.195} 2.122.179.94 (talk) 15:49, 27 August 2021 (UTC)[reply]

It is quite surprising (to me) how narrow the wavelength range is that we can see: the article Electromagnetic spectrum illustrates this well. Both Infrared spectroscopy and Ultraviolet spectroscopy are of use to chemists who wish to identify materials, since as Jayron32 says, molecules can absorb right across that range. The article on chlorine, for example, has its absorption lines which lie in the visible range shown in its Chembox. Mike Turnbull (talk) 16:35, 27 August 2021 (UTC)[reply]

Actually, what I've just written may be misleading: the spectrum shown for chlorine is its emission spectrum, not its absorption spectrum and nitrogen has many emission bands in the visible range, so based on that it might be thought it should be colored also. The relationship between absorption and emission depends on the Einstein coefficients. Mike Turnbull (talk) 16:49, 27 August 2021 (UTC)[reply]

Not exactly; the Einstein coefficients determine the intensity of the absorption and emission (stricto sensu, the determine the likely hood that an absorption or emission event will occur). The actual color of the lines exactly matches up, so if a black line appears at a specific color in an absorption spectrum, that color line will appear in the same element's emission spectrum. --Jayron 32 17:04, 27 August 2021 (UTC)[reply]

Chlorine's emission spectrum

Nitrogen's emission spectrum

Thanks for the clarification, Jayron32. So now I'm becoming puzzled as to why nitrogen is colorless, given all the lines in comparison to chlorine! ;-) Mike Turnbull (talk) 17:50, 27 August 2021 (UTC)[reply]

Because the Einstein coefficients are so low. Basically, there are lots of absorbed colors of light, but the likelihood that an actual absorption event takes place is very very low, making it essentially colorless. In high-energy environments (like in stars or flame or things like that), there's usually enough emission/absorption so you can easily see the spectrum. In room temperature, atmospheric pressure, some substances have such low likelyhood of absorbing the light that you don't see any meaningful colors. --Jayron 32 17:56, 27 August 2021 (UTC)[reply]

The colour can be helped along by condensing the gas (which, of course, greatly increases the density and hence the likelihood of getting an absorption event). That's why liquid oxygen shows a clear blue colour whereas gaseous oxygen doesn't (and here it's quite bad because the absorption event involves pairs of O₂ molecules which are harder to get together as a gas). Double sharp (talk) 03:17, 28 August 2021 (UTC)[reply]

Thank you!

I did some more research further to Jayron32's answer; the subsequent discussion; and clues provided therein. An explanation somewhat related to that of Jayron32 is provided by this site.

Noting H, N, O are relatively light, strongly bonded molecules, the site mentions that:

"The inviting blue of a mountain lake or a sea is unique in nature, in that it is caused by vibrational transitions involving hydrogen bonding…

…Most molecules have vibrational energies that are lower in frequency (longer in wavelength)…falling in the range of far infrared or thermal vibrations rather than in the visible light range. The hydrogen atoms in water are very light, and the bonds between hydrogen and oxygen very strong, which shifts them to higher frequencies (with shorter wavelengths), with overtones that lie in the range of visible light. Just as the pitch of a vibrating string is raised if the mass of the string is reduced and the tension applied to the string is increased, so too the highest-frequency vibrations occur with the lightest atoms (hydrogen) when most strongly bonded (to oxygen in water)."

For heavy water, this is heavier enough than ordinary water to apparently shift its absorption spectrum to higher wavelengths outside of the visible spectrum of light (never mind H bonding). Heavy water is thus colorless. I guess this is why H₂O₂ hydrogen peroxide is also colorless.

Things get confusing at this point.

In this JChemEd article[3] on why liquid oxygen is blue, the author writes:

"A substance appears colored to the human eye when it absorbs a portion of the visible spectrum (4000 to 7000 A). Since the energy of a quantum of visible light is very much greater than that required to excite vibrations and rotations in molecules, absorption of visible light can normally be traced exclusively to the excitation of an electron from one energy level (state) to another."

It seems then that the lightness of H, N, O or the strength of their bonding (436 to 945 kJ/mol) compared to the fluid halogens (159 to 242) doesn't have anything to do with their appearance(?), if this is instead related to "excitation of an electron from one energy level (state) to another."

For H, this forum[4] says:

"Molecular hydrogen does not begin to absorb until you get into the vacuum ultraviolet. The hydrogen atom in its ground electronic state (n=1) also does not absorb any light until you get into the vacuum ultraviolet. For the atom, the first absorption is Lyman alpha (121.5 nm). For molecular hydrogen, the first absorption is at even shorter wavelengths (ca. 110 nm)."

For N, this journal article[5] notes, "Strong absorption bands in the range 80–100 nm shield the Earth's surface from the extreme ultraviolet (XUV) part of the solar radiation."

For O, this JChemEd author[6] mentions the six lowest energy states of oxygen lie in the IR, near visible, or UV, and that, "There are no other states of O₂ which can give rise to absorption bands in the visible region." For liquid O₂ they mention the possibility of one photon simultaneously elevating two electrons on two different molecules to excited states…twice the energy required to excite a molecule…is possessed by a photon at 6340 Å (= red). I gather such a possibility is more likely in liquid oxygen, where the molecules are closer together, perhaps in the form of nano-meter scale clusters of solid oxygen.

Ozone O₃ is pale blue, and heavier than oxygen, and has a lower average bond strength of ca. 300.[7]. I'd've thought that being heavier and having a weaker bond presumably shifts its absorption spectrum to lower (visible) wavelengths. Instead it appears to be due to electron excitations, perhaps in the same manner as what happens to liquid oxygen?

The halogen fluids remain puzzling, including the violet color of iodine vapor. They're colored and get progressively darker going down the group. If this isn't related to their weak bonds and increasing atomic weights, but instead to electron excitations, why is it they're colored whereas H, N, O aren't, and why does the color get progressively darker?

Our article on Absorption spectroscopy says:

"The frequencies where absorption lines occur, as well as their relative intensities, primarily depend on the electronic and molecular structure of the sample. The frequencies will also depend on the interactions between molecules in the sample, the crystal structure in solids, and on several environmental factors (e.g., temperature, pressure, electromagnetic field). The lines will also have a width and shape that are primarily determined by the spectral density or the density of states of the system."

Unfortunately, this doesn't help.

I know that in going down a group such as the halogens, atomic radius increases, the pull on the valence electrons from the nuclear charge becomes less strong; and that (presumably) their valence electrons become easier to excite.

But what is that influences the energy levels of the excited states, which determine the colors, or lack of colour, involved? Is it related to the atomic radius, and to Z, both of which figure in the Rydberg formula and the Rydberg constant?

I'm asking these questions in the context of bringing nonmetal up to FAC standard. It's currently undergoing peer review. Sandbh (talk) 07:22, 28 August 2021 (UTC)[reply]

The problem is that the Rydberg formula ONLY works for two-particle systems, essentially hydrogen or any ion that contains only a single electron, like Li²⁺ or something like that. Once you deal with real atoms and molecules, there is no meaningful mathematical solution; it becomes a quantum n-body problem, and there's no way you can tie the observed spectrum to any mathematical formulation which would predict that pattern of lines. Heck, even the Schrödinger equation has only been quantitatively solved for hydrogen atoms. For any larger atoms or molecules it can only be approximated. --Jayron 32 20:44, 29 August 2021 (UTC)[reply]

In case that sounds too pessimistic, it is worth pointing out that chemists regularly look at IR spectra, note the presence of an absorption band and say "this shows that the molecule contains such-and-such functional group". Carbonyl groups are especially useful in this context. On the other hand, as Jayron32 implies, the details of the so-called "fingerprint region" are usually a mystery. Mike Turnbull (talk) 10:36, 30 August 2021 (UTC)[reply]

Yes, but the IR bands are determined empirically. Like "We know this is the carbonyl band because we've checked a bunch of C=O containing compounds and found this band and worked out it comes out here". There's no way to work out the electron energy levels ahead of time and mathematically figure out that there should be a C=O stretch band at that location, it's purely a result of experimental results. --Jayron 32 11:54, 30 August 2021 (UTC)[reply]

Cutting steel temperatures.

You know the metal spinning wheel used to cut metal bars? I believe it is easier to cut metal when the bars are hot. Someone said "not all metals." So some metals are actually easier to cut at room temperature? I find this hard to believe. Both the wheel and the bars get hot. 67.165.185.178 (talk) 17:29, 27 August 2021 (UTC).[reply]

You seem to be talking about Grinding (abrasive cutting). That article may be a good place for you to do your research. --Jayron 32 18:02, 27 August 2021 (UTC)[reply]

What was the earliest time in the history of the universe for which there is direct evidence?

In the context of the Big Bang theory, what is the earliest time (or temperature scale, or the smallest scale) for which there is direct evidence? The CMB shows that the observable universe definitely existed at temperature of about 3,000 K, with the observable universe being something like 40 million light years in radius [8]. I would say that the observed isotopic ratios in the present universe constitute direct evidence that something like Big Bang nucleosynthesis occurred, which shows that the entire observable universe was hot enough for nucleosynthesis to occur. This apparently constitutes indirect evidence that the universe was at such-and-such scale factor at that time, but maybe it's direct evidence.

But is the Big Bang nucleosynthesis epoch the earliest stage for which we have direct evidence? In popular science presentations, it's typical to point to particle colliders like the LHC to show that we have direct evidence of how the universe behaves at energy scales and densities which would correspond to the Electroweak epoch. We surely know that portions of our observable universe can reach those energy scales with no issue. However, do we actually know that the entire observable universe was once at that electroweak temperature (and scale, and time corresponding to the Big Bang theory)?

Put another way, let's imagine we had a particle collider which could probe the Grand unification scale. That would show that parts of the universe can get that hot, but it alone doesn't demonstrate that the observable universe actually was that hot at some point in the past. So, what's the earliest time for which we can definitely say that the universe existed? BirdValiant (talk) 18:13, 27 August 2021 (UTC)[reply]

It depends on what your standard for "direct evidence" is. For example, the fact that nuclei exist could be seen as direct evidence that nucleosynthesis happened at some point. If you mean "what is the earliest we can look out into the sky and see stuff from", that's the CMB, which represents a sort of visual horizon earlier than which we can't see. That's because the CMB is the oldest light we can see, we literally can't detect anything else from any earlier point. --Jayron 32 18:21, 27 August 2021 (UTC)[reply]

Detection of the cosmic neutrino background would bring us to 10 billion Kelvin or one second after the Big Bang. The PTOLEMY experiment is being developed to do that. --Wrongfilter (talk)

@Wrongfilter: So at the current state of the art, would it be correct to say that the earliest time in the chronology of the universe for which we have direct evidence is 370,000 years after the theoretical beginning of the Big Bang? And also that we have direct evidence that something like Big Bang nucleosynthesis occurred, which then is indirect evidence that the universe was at the scale and temperature regime of a few minutes after the theoretical beginning? BirdValiant (talk) 18:54, 27 August 2021 (UTC)[reply]

Disregarding all philosophical subtleties as to what constitutes "direct" evidence, I'd say yes. Being pedantic, the direct evidence is that there is a sea of photons now at a temperature of 2.75 K. That these photons were last scattered at a temperature of 3000 K is inferred, and I leave it to you whether you want to call that direct or indirect. --Wrongfilter (talk) 19:09, 27 August 2021 (UTC)[reply]

@Wrongfilter: Beyond the cosmic neutrino background (for which there is already indirect evidence in the CMB), are there any avenues of research on the horizon which could push the timeline back further from the 1 second point? I'm reminded of the B-mode polarization from 2014 which pretty much has been discounted due to cosmic dust, but maybe primordial gravitational waves could be found somehow. I guess that if we had a really good model for baryogenesis and tested it in other ways, and then used it to predict the predominance of matter over antimatter, that would be somewhat similar to the way our pre-existing understanding of nuclear fusion combines with primordial isotope data to provide evidence of BBN. Or maybe if cosmic strings or magnetic monopoles or something were found, that'd be something too. But maybe there are other avenues of which I am not aware. BirdValiant (talk) 00:09, 28 August 2021 (UTC)[reply]

There is no evidence, direct or otherwise, that is accepted by Young Earth creationists. They believe that the universe was created no more than 10,000 years ago, and that the Creator stuffed the young Earth with newly created fossils to make it appear much older. The cosmic background radiation from which scientists extrapolate early events was created at the same time as well. In short, the Creator created a new universe that was indistinguishable from one that already had a history of more than 13 billion years; any "evidence" that makes scientist adhere to the Big Bang theory was actually created relatively recently. --Lambiam 20:49, 27 August 2021 (UTC)[reply]

This as a science reference desk, not a theology reference desk or forum. What young Earth creationists believe is of no relevance here. AndyTheGrump (talk) 00:34, 28 August 2021 (UTC)[reply]

Is there direct evidence that the universe was not created 2.5 seconds ago (or at 3pm last wednesday), along with all of its inhabitants complete with their memories? I think there is a name for this puzzle but I don't know what it is. Also, idk much physics, but I had the impression that at very high densities like in the big bang era, the concepts of space and time didn't really apply like we normally think of them. Something similar happens near black holes. 2601:648:8202:350:0:0:0:2B99 (talk) 03:34, 28 August 2021 (UTC)[reply]

The name you want is the omphalos hypothesis. It is of no scientific value because it cannot be used to make any verifiable predictions, so I suggest there's no reason to discuss it here. --184.144.99.72 (talk) 04:46, 28 August 2021 (UTC)[reply]

The theory that the universe has existed for more than two days does not produce much in the way of verifiable predictions either. --Lambiam 07:58, 30 August 2021 (UTC)[reply]

Thanks, five-minute hypothesis (linking to part of that article) was the version I had in mind. I dunno that verifiable predictions are that important for a theory, if it has good explanatory power (e.g. GR's predictions about black hole interiors are unverifiable because there is no way to make observations there and get the data out, but GR is still a good theory). The 5-minute hypothesis of course doesn't explain much either ;). 2601:648:8202:350:0:0:0:2B99 (talk) 09:07, 28 August 2021 (UTC)[reply]

August 28

C. J. Field and Edison lighting

Who was C. J. Field, who wrote the chapter "Design and Operation of Incandescent Stations", in the 1890 book Incandescent Electric Lighting. A practical Description of the Edison System? Both the other contributors were associates of Edison; was Field? Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 19:49, 28 August 2021 (UTC)[reply]

Looking in Newspapers.com (pay site), I'm seeing various references to a C. J. Field, who was a student of Edison's among many others. One article, in a Boston paper in 1911, says he's the president of the Electric Omnibus and Truck Company, wherever that may be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:16, 28 August 2021 (UTC)[reply]

The Electric Omnibus and Truck Company was based in NYC.^[9][10] --Lambiam 07:57, 29 August 2021 (UTC)[reply]

Omnibus, in this context, is just an old word for a bus. From the links here and below, the company must have produced battery-powered buses and trucks. --184.144.99.72 (talk) 09:40, 29 August 2021 (UTC)[reply]

Cornelius James Field (1862-1915). Here's a clipping someone made at Newspapers.com, which theoretically should be visible to anyone.[11] (You can put that theory to the test.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:24, 28 August 2021 (UTC)[reply]

Baseball Bugs, I am not a Newspapers.com subscriber, but I can confirm that I can see the article just fine. What a fascinating (and probably notable) man, who should probably be mentioned in articles about the early history of electric vehicles. That's a photo of a 110 year old electric car that I took. Cullen³²⁸ Let's discuss it 04:15, 29 August 2021 (UTC)[reply]

Sounds like he's notable enough to have his own Wikipedia article. --184.144.99.72 (talk) 05:41, 29 August 2021 (UTC)[reply]

He gets a mention here (bottom right) along with his Field Engineering Company. More details here and here. Alansplodge (talk) 20:40, 29 August 2021 (UTC)[reply]

Great work, thank you all. Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 18:18, 29 August 2021 (UTC)[reply]

August 29

How can low pressure area over oceans create rainfall in coastal areas?

I didn't understand the relation between pressure area and rainfall. I believe rainfall just a Precipitation product. Then why this page say different to what I believe? Rizosome (talk) 03:42, 29 August 2021 (UTC)[reply]

Hello, Rizosome. This website gives a good introductory explanation. I am not an expert, but my understanding is that extremely moist air masses usually accumulate over seas and oceans, which make sense. Low pressure areas draw in these moist air masses, and the low pressure also causes these air masses to rise much higher in the atmosphere, and the higher you go, the colder it gets. Liquid water or ice crystals condense out of moist air as it cools. The result is rain and snow. Prevailing winds often carry these weather systems over land masses. If there are mountains along these coastlines, they will also force the air masses even higher. That additional height intensifies the rain and snow. If my remark is not accurate, I am sure that a smarter editor will correct me. Cullen³²⁸ Let's discuss it 04:01, 29 August 2021 (UTC)[reply]

August 30

Easily obtained references for temperature other than ice water and boiling water?

Are there any other ways to obtain accurate known temperatures (for calibrating a thermometer between 0 and 125 °C) other than boiling water and ice water? Thanks. 02:41, 30 August 2021 (UTC)

I am not sure of other ways, but I do know that the temperature of boiling water is not necessarily 100 °C except at sea level and at normal atmospheric pressure. For example, water boils at about 94.4 °C in Denver, Colorado and about 70 °C at the summit of Mount Everest. The boiling point also varies a bit if atmospheric pressure is higher or lower. So using boiling water for calibration purposes requires accurate elevation data, an accurate barometer and some accurate mathematical calculations. Cullen³²⁸ Let's discuss it 06:08, 30 August 2021 (UTC)[reply]

This may sound like cheating, but in both industrial and scientific contexts, the usual procedure for calibrating thermometers is by comparison with high-precision accurate thermometers, such as quartz thermometers. These need to be calibrated themselves, of course; ultimately, the standard is now grounded in combining the Boltzmann constant with measurements of the kinetic energy of a gas, which requires a sophisticated laboratory set-up. In theory, the freezing or boiling points of other substances than H₂O could be used as reference points, but such substances are not easily available in pure or standardized form, or are hazardous, or their phase-transition temperatures are outside the range of interest. --Lambiam 07:45, 30 August 2021 (UTC)[reply]

See also Triple_point#Triple-point_cells. The triple points are much more precisely defined than melting/boiling points. —Kusma (talk) 08:57, 31 August 2021 (UTC)[reply]

Depending of what "easily obtained" means... I worked with a differential scanning calorimetry device whose standard operating procedure called for periodic calibration using small pellets of pure (>99%) indium and gallium. I did not perform the calibration myself but they explained to me that the main was to check that the heat flux sensor does not drift (because you know the enthalpy of fusion of pure metals within a ridiculous value). Looking around the manufacturer’s site it is also used to check the temperature measurement (because you know the melting point within an even more ridiculous value).

I believe for that device the temperature was validated but not calibrated (you just check if the measurement is right and if not you call the maintenance person, you do not adjust a knob to make the measurement fall on the expected value). However looking around I found "How to correctly calibrate a Differential Scanning Calorimeter" on the Linseis website (blacklisted so I cannot link) which implies their DSC devices do have an adjustable knob for temperature.

For OP’s purposes, assuming they are ok with melting heavy metals in their equipment, indium (around 160°C) is a bit too high for the asked temperature range you reference, but gallium (around 30°C) is a fine lower point I think. Tigraan^{Click here for my talk page ("private" contact)} 15:32, 31 August 2021 (UTC)[reply]

Melting point for many (but not all) substances tends to be a fairly sharp and easy-to-determine thing under consistent conditions. A melting-point apparatus is a relatively simple device that many chemistry students will be familiar with. --Jayron 32 16:01, 31 August 2021 (UTC)[reply]

I've done dozens of melting point determinations, usually of new compounds I had just made but I can't think of a readily-available household material with a reliable melting point to act as a standard for the upper end of the 0 – 125 °C range. Access to ice water makes the standard for 0 °C readily available. Benzoic acid is cheap and readily available from chemical suppliers, with M.P. = 122 °C. It's not really "household", however. Does anyone have a better suggestion? Mike Turnbull (talk) 11:51, 1 September 2021 (UTC)[reply]

Or maybe use the smoke point of some appropriate oil? (The article does mention that the value can vary with storage, so it will be less precise than a chemistry method based on a pure compound.) Tigraan^{Click here for my talk page ("private" contact)} 15:23, 2 September 2021 (UTC)[reply]

How can we balance a ring like a rocks if it's center of gravity present in air?

if center of gravity of any object present in air, doesn't that make object unbalance forever? Rizosome (talk) 05:21, 30 August 2021 (UTC)[reply]

The sum of force vectors is the relevant thing, in mechanical equilibrium (balance). If a ring such as doughnut rests on a table, every point of the ring is acted on by a force due to gravity, which is balanced by a normal force due to the surface of the table. The sum of the force vectors is zero, so the doughnut doesn't topple over or go anywhere. However, if the doughnut in the same orientation rests on the tip of your finger, the hole at the center of gravity means it can't be balanced (or is not static). Card Zero (talk) 06:46, 30 August 2021 (UTC)[reply]

(ec) The question is not entirely clear. Whether an object is balanced or not is not an intrinsic property of the object, but depends on its orientation in a stationary reference frame with respect to the forces acting on it. As a first approximation, for a ring not having momentum touching a horizontal plane beneath it while the only acting force is a uniform vertical field of gravity, there is an equal but opposite force of reaction (see Normal force). If there is only one point of contact between the ring and the plane, and the upward vector from the point of contact passes through the centre of gravity of the ring, the ring is balanced. --Lambiam 07:18, 30 August 2021 (UTC)[reply]

Think about say a funnel, its cg is obviously in the air, yet it obviously has at least one stable orientation on a flat plane (wide end down), and one metastable (lying on its side). Greglocock (talk) 01:36, 31 August 2021 (UTC)[reply]

Or consider a tennis ball. Rizo occasionally just skipping thinking. 2003:F5:6F0A:4700:3DAA:6206:2192:B77C (talk) 18:15, 2 September 2021 (UTC) Marco PB[reply]

Actually, I'd swap those two. The lying on its side is the stable orientation (though it rolls) given that that orientation places the center of mass at the lowest point; it has the lowest potential energy of any orientation, and as such, by definition it is the most stable. The "resting on the wide end" is metastable because it has a higher COM, and so has a higher potential energy. It is metastable because it requires significant additional energy to knock it over (metastable systems are at a local potential energy minimum, but not absolute potential energy minimum), but presuming a flat surface, the one on its side has lower gravitational potential energy. --Jayron 32 17:43, 31 August 2021 (UTC)[reply]

But the question is about balancing, not about stable orientations. In colloquial language, having an object be in a stable orientation (in the sense that minor perturbations do not decrease its potential energy) is not considered a balancing act. --Lambiam 21:14, 31 August 2021 (UTC)[reply]

August 31

Why do historians believe planets revolve around Earth?

What made them to believe like that? What mathematical formulation did they follow to prove that? Rizosome (talk) 05:59, 31 August 2021 (UTC)[reply]

They didn't use any math. They simply believed that where they were (the earth) was the center of everything. See Geocentric model. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:41, 31 August 2021 (UTC)[reply]

"They" used a lot of math, "they" being the Ancient Greeks (as summarised in the Almagest of Ptolemy) and the Christian and Islamic scholars who followed them (I'm a bit puzzled by what "historians" is supposed to mean, "historic people" or something?). The most important idea in the mathematical description were epicycles. --Wrongfilter (talk) 07:01, 31 August 2021 (UTC)[reply]

Yes, they used math after-the-fact, to rationalize their ancient and flawed model, which was based strictly on belief. Presumably the OP should have said "did" rather than "do". Or something like that. And it was religious authorities, more than historians, who promoted this belief, to the point where anyone who questioned it was branded a heretic. Anyway, the article lists the two main observations on which their belief was based. And for routine day-to-day life, those geocentric observations work fine. The sun appears to rise and set every day. The stars appear to revolve slowly around us through the year. And the apparent retrograde motion of the planets is just a curiosity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:23, 31 August 2021 (UTC)[reply]

Speaking of religious authorities...Galileo Galilei died in 1642. Finally, in 1992, Pope John Paul II admitted that the Church had made an error, by accusing him of heresy. Only took 350 years! Tribe of Tiger ^{Let's Purrfect!} 19:45, 2 September 2021 (UTC)[reply]

Given their naive assumption that the Earth was a flat and stationary surface (neither moving nor spinning), the conclusion of the earliest astronomers that the Sun and the planets alike orbited around Earth was based on observation rather than belief – the main belief aspect being that the lights that came up in the east were the same celestial bodies as the ones that had sunk to the west half a day before, and not newly created light sources. The naive assumption was, of course, a belief, but (I think) purely because no thought of any other possibility crossed their collective mind. Aristarchus of Samos (c. 310 – c. 230 BCE) was the first of a few rare exceptions, but his ideas were not well received, and it took another century before the idea took hold among astronomers that the Earth was in fact a globe – while sticking to the geocentric model. Moreover, the belief or assumption was that the "fixed stars" were fixed to a revolving celestial sphere, while the "wandering stars" (the planets) were moving about on or near that sphere. The notion of "proving" any of this mathematically is not appropriate, also not for modern astronomical models. The proof of any theory in the natural sciences is based solely on observation. --Lambiam 08:43, 31 August 2021 (UTC)[reply]

I see your point. The true "belief" is that we can trust what we observe. In the realm of science, theories can change when new observations come along. When theocrats and other politicians get involved, it interferes with the scientific process. (That is not exactly a news flash!) ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:56, 31 August 2021 (UTC)[reply]

Counterpoint: planets do revolve around Earth. In the geocentric celestial reference system, that is. Why do you think they do not? What mathematical formulation lead you to the belief that planets revolve around the Sun?

(OK, ellipses are cleaner than pericycles, but once you have Newton’s laws and the formulae for non-inertial reference frames, you can do the calculations just fine.) Tigraan^{Click here for my talk page ("private" contact)} 08:31, 31 August 2021 (UTC)[reply]

Why are you muddying the waters? Imagine the effort needed to reconcile this model with the theory of relativity. I doubt you can do the calculations "just fine". --Lambiam 08:50, 31 August 2021 (UTC)[reply]

Calculations in non-inertial reference frames is fairly basic. I studied it towards the end of my first year of physics bachelor. The second paragraph of the lead of Coriolis force is a good plain-language explanation; if you want an exercise in checking that the results are consistent with the inertial frame calculation, I found this textbook in about ten seconds of search.

At any rate, I would not call it a "model" when it really is pure math, just like using cartesian or polar coordinates to describe the equations of motion (one is probably easier than the other depending on what problem you want to solve).

On the other hand, involving relativity, Lorentz transformations etc. for stuff that can be well-approximated by classical mechanics does muddy the waters quite a lot, both as a matter of physical hypotheses and as a matter of calculations to work through. Tigraan^{Click here for my talk page ("private" contact)} 15:11, 31 August 2021 (UTC)[reply]

I used "model" in the sense of "mathematical model", a description of a real-world system in the form of a collection of mathematical formulas. And I invoked relativity because in that model the speed of material objects can routinely exceed 300,000 km/s, while the speed of light is not constant. But also without invoking relativity, it violates the most basic forms of symmetry, such as the translational invariance of the laws of physics. --Lambiam 21:05, 31 August 2021 (UTC)[reply]

Any particular reference frame is feasible to use, given the amount of mathematics your willing to do to transform measurements in one frame to another. Which reference frames are useful is a different story, and for many reasons, the heliocentric model works well for most applications for anyone who isn't interested in pursuing an advanced physics degree "I learned it in my first year in my physics bachelors" already puts it out of range of 99.99% of the human population, but other simpler models are both a) easier for everyone else to understand and b) correct enough for them to use. --Jayron 32 17:33, 31 August 2021 (UTC)[reply]

Distance change between moon and earth per year - strange development

Looking at the numbers given in Lunar distance (astronomy)#Orbital history, the distance between earth and moon has changed per year in the following magnitudes:

Distance	years ago	Distance increase / year (Averagre from then until now)
384.400 km	now	3,8 cm (measured)
383.000 km	80 million years	1.75 cm
332.000 km	2.5 billion years	2.1 cm
24.000 km	4.5 billon years	8 cm

This would mean that the 'speed' of the moon increasing its distance from earth would have gone from some much higher value in the early stages (probably more than 20 cm or maybe even much more) down to ca. 2 cm per year - and has now doubled again within a fairly short time. Does this make sense? Can it be accurate? --KnightMove (talk) 10:43, 31 August 2021 (UTC)[reply]

A pretty good bet is that continental drift has changed how ocean tides function over geological timescales, which feeds back into the Moon's recession rate. Lunar distance mentions the current unusual rate and has some links to research papers. 85.76.66.247 (talk) 12:20, 31 August 2021 (UTC)[reply]

The tides also get 8 times less powerful for each doubling of distance, they were tsunami height at first. Sagittarian Milky Way (talk) 17:18, 31 August 2021 (UTC)[reply]

Well after the first ocean formed. Sagittarian Milky Way (talk) 18:17, 31 August 2021 (UTC)[reply]

4.5 billion years ago, there were no oceans with which to have tsunamis, given that a Mars-sized planet had just collided with the Earth. The earliest oceans on Earth would have been no older than 4.28 billion years ago, and a more conservative estimate puts that at no older than 3.8 billion years ago. --Jayron 32 17:24, 31 August 2021 (UTC)[reply]

I distinctly remember PBS or something saying the tides were still very high when there were already oceans, but yes a big gap in between. Sagittarian Milky Way (talk) 18:17, 31 August 2021 (UTC)[reply]

A new model of the formation of the Moon has invoked the presence of a magma ocean at the time of the giant impact, see here. So, after the formation of the Moon there would have been large tides in the magma ocean. Count Iblis (talk) 02:35, 1 September 2021 (UTC)[reply]

I have better memories of Blondie's version of the song. --Jayron 32 16:03, 1 September 2021 (UTC)[reply]

September 1

Is infinite zoom originated from Mandelbrot set?

Is infinite zoom originated from Mandelbrot set? Rizosome (talk) 03:44, 1 September 2021 (UTC)[reply]

What is Infinite zoom? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:04, 1 September 2021 (UTC)[reply]

This is example of infinite zoom. Rizosome (talk) 05:42, 1 September 2021 (UTC)[reply]

The Powers of Ten films precede the discovery of the Mandelbrot set. The 1977 version starts with a zoom out from a human scale to one in which clusters of galaxies are mere points of light, and then zooms back in to the original image and continues to the subatomic level. Long zoom sequences had been made before in films, but nothing as long as this. --Lambiam 08:06, 1 September 2021 (UTC)[reply]

No, it is more related to the Droste effect. The Mandelbrot set is a mathematical description which, when visualized, gives a cool fractal geometry. Since this visualization is self-similar, an animation of it will show (approximately) repeating patterns when zoomed enough. Rmvandijk (talk) 09:36, 1 September 2021 (UTC)[reply]

A zoom on the Mandelbrot set can be seen here (Youtube) or you can choose your own area of zoom here. Mike Turnbull (talk) 11:23, 1 September 2021 (UTC)[reply]

It should be noted that while the visualizations of the Mandelbrot set are self-similar, being self-similar is not a defining characteristic of fractals. See This video for a good explanation of fractals and their properties. --Jayron 32 16:00, 1 September 2021 (UTC)[reply]

Are there any good organizations that help specifically Narwhals?

Are there any good organizations that help specifically Narwhals? 2001:569:7D98:E00:98C2:EEE7:2572:77E4 (talk) 04:20, 1 September 2021 (UTC)[reply]

I don't think that Narwhals specifically need support since their habitat is the Arctic and their conservation status is "least concern" (see ref in article you linked to). However, you can find charities that support sea creatures by Googling Narwhal + charity (which gives ORCA and WWF, for example). Mike Turnbull (talk) 11:33, 1 September 2021 (UTC)[reply]

It should be noted that, according to Narwhal, the species was, until recently, categorized as "nearly threatened"; meaning that conservation efforts were needed to raise their numbers. There may be some concern that additional efforts are needed to maintain good, healthy populations given their recent status change. The World Wildlife Fund has information on their narwhal conservation efforts here. Perhaps the OP could look into that organization. --Jayron 32 15:59, 1 September 2021 (UTC)[reply]

Thank you Jayron32. I will look into the organization! 2001:569:7D98:E00:98C2:EEE7:2572:77E4 (talk) 20:08, 1 September 2021 (UTC)[reply]

September 2

Does fluctuations in brightness of bulb visible if it done like this?

AC current means frequency more than 0. So at less frequency of AC (below 50hz), fluctuations in brightness of bulb visible to human eyes? Rizosome (talk) 01:38, 2 September 2021 (UTC)[reply]

As suggested in Utility frequency, if it drops below 60 or 50 it can produce noticeable flickering. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:54, 2 September 2021 (UTC)[reply]

See also Flicker fusion threshold. Whether flicker is perceived at 50 Hz depends strongly on the depth of the modulation. The power delivered is proportional to the square of the current, which for alternating current means that the power frequency is twice that of the frequency of the current. In a formula,

\left(\exp j\omega t\right)^{2}=\exp j(2\omega )t.

This means that the effective (light strength) frequency for incandescent light bulbs is twice the nominal frequency, so 50 Hz AC becomes 2 × 50 Hz = 100 Hz. Also, for such bulbs, the filament cools down only very little when the current passes through zero, so they keep emitting light with only minor changes in intensity and the flicker is not perceptible to the human eye. It will probably remain imperceptible at 35 Hz. With some older types of fluorescent tubes that basically went on and off, the flicker could be annoyingly noticeable also at 60 Hz. Some older CRT displays also had perceptible flicker at these frequencies. --Lambiam 09:58, 2 September 2021 (UTC)[reply]

Edward Sonstadt

Edward Sonstadt was a British chemist. He made magnesium ribbons for photography in 1860s. Does anyone have his photo? Thanks in advance.

Gold anchor chain

Is it possible to make an anchor chain out of solid gold (as described in Alexander Green's novel of the same name), or would it break under the weight of the anchor and/or the stress placed on it by the momentum of the ship? If this is in fact possible, would it be a good way to hide stolen gold (as also related in the same novel)? 2601:646:8A81:6070:5CE9:B4CB:370A:7A2C (talk) 06:43, 2 September 2021 (UTC)[reply]

Mechanical the strength of gold is only about a fifth of a steel, that could be used for an anchor chain. Links of a golden anchor chain therefore would have to be scaled up accordingly (cross-sections, five-fold). This would increase the weight of the chain fifteen times, so it probably wouldn't be manageable for that certain actual use any more. However, it's just lying around on the ship it could still serve as sort of hiding place. --87.147.179.79 (talk) 12:29, 2 September 2021 (UTC)[reply]

How did you calculate the 15 times? scaling the cross section with 5 scales the volume with 5^(3/2), which my calculator makes as ~11.2. A quick calculation shows that, with a yield strength of 80 MPa (N/mm2), to anchor a 10 tonne boat you'd need shackles with a total cross sectional area of 1226mm, or about 13mm radius for 2 circular sections. That is a lot bigger than the steel chains you'd use but a useful ruse in calm weather. I'd hide it at the bitter end of the chain and not (actively) use it. Rmvandijk (talk) 13:45, 2 September 2021 (UTC)[reply]

I did mean with ″cross-section″ the ″cross-sectional area″. And for the material-strength I made an estimated guess (is that a correct English expression?), thus as steel is about five times stronger. Same regarding the densities, thus as gold is about three times denser than steel: 15 results from 3 times 5. --87.147.179.79 (talk) 19:02, 2 September 2021 (UTC)[reply]

Ancient horses

Were there any differences in appearance between ancient horses (classical antiquity until Roman times, e.g. those in cavalry) and modern horses due to selective breeding (assuming the same breeds perhaps)? 212.180.235.46 (talk) 18:16, 2 September 2021 (UTC)[reply]

The Nisean horse breed was apparently large and robust. Following the rather patchy links from that article, it seems to be possibly of the archetype "forest horse" which is also called "hypothetical warmblood subspecies" in History of horse domestication theories, and may have been the ancestor of the Latvian horse and the Groningen horse. So that gives you a vague and dubious impression of what some horses from classical antiquity looked like. Horses in the Middle Ages says "During the Decline of the Roman Empire and the Early Middle Ages, much of the quality breeding stock developed during the classical period was lost due to uncontrolled breeding and had to be built up again over the following centuries," confirming at least that there was such a thing as horse breeding in classical antiquity. Card Zero (talk) 19:27, 2 September 2021 (UTC)[reply]

Qualifying for organ/tissue donation

I have been registered as an organ donor on my driver's license, for decades. Now, I am a six year (breast) cancer survivor, plus I'm in my early 60s. Are my organs/tissues still of use, despite my previous cancer? This seems possible. ^[1] But what about a person's age, in regards to various organs and tissues?

Also, I "read something" where the child of an end-of-life, unconscious/comatose parent, said they were dissuaded from providing their parent with opioid medications, because this would prohibit the organs from being transferred to a person who needed them. (Do opioid meds truly ruin the organs?) Haven't found the answers, thus far, in WP articles. Thanks, Tribe of Tiger ^{Let's Purrfect!} 19:49, 2 September 2021 (UTC) [reply]

References

^ "Can I Donate My Organs if I've Had Cancer?". www.cancer.org.

Negative prices for electricity

It seems that when the sun is shining and the wind is blowing, and there are not enough people turning on their AC, sometimes the electricity gets so cheap that you actually need to pay to get rid of it. Why's that? Why not handle that surplus of energy by attaching 2 wires to a big chunk of steel and let it melt? Even if you won't use the stored energy and open a window to release the heat, you'd still make money in a way that the electricity companies must have thought about themselves. So, what's so hard about getting rid of excess electricity? Joepnl (talk) 20:46, 2 September 2021 (UTC)[reply]

[1] "Can I Donate My Organs if I've Had Cancer?". www.cancer.org.

[1]