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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]

[un-indent] Actually, there was a seemingly good reason why they concluded that the earth was at the center of the universe: their reasoning was that if the earth moved relative to the "fixed stars", then they would likewise seem to move from their places from one night to the next, and since this was decidedly not observed, they concluded that it couldn't possibly be the case! (The reason for their error was, this apparent movement is so tiny -- less than 1 arc second even for the nearest star of all -- that not only is it impossible to see with the naked eye, but even to measure with a mariner's sextant, you need a telescope with at least 60x magnification and high-precision adjusting gear to detect it at all, which was not something available in the ancient world!) 69.181.91.208 (talk) 09:33, 3 September 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]

Classical-era horse breeding was certainly a thing. Xenophon had something to say about it in his ~355 BCE textbook On Horsemanship (which in translation is very readable) and there are surely other surviving classical treatises on the subject (about which I'm not an expert). Further, we have quite a few equine carvings and statues from the classical era, which illustrate how horses then looked, and differed from wild breeds. We have been selectively breeding horses for more than 5,000 years. See also List of horse breeds#Archaic types. {The poster formerly known as 87.81.230.195} 2.122.0.2 (talk) 15:52, 3 September 2021 (UTC)[reply]

That last link you gave is about the Middle Ages, when horses were classified by how they looked and what they were for, and so they weren't being selectively bred, at least not deliberately. (Or should that be "not carefully"?) That's why I was unsure to what extent the ancient Greeks (etc.) were selectively breeding them. Card Zero (talk) 20:06, 3 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.

It's good to hear you're doing well. There have been well-reported cases of cancer survivors whose organs were transplanted into someone and the cancer recurred. It's likely that the cancer survivor's immune system was successfully keeping the cancer in check, but there were a few cancer cells lurking around which could cause cancer when transplanted into someone immunosuppressed. I can't find the specific paper I'm thinking of, which is annoying as I think I remember a lot about it-if I recall right it was published by a team at Ninewells Hospital, Dundee and concerned a melanoma survivor who'd died for unrelated reasons. I think it was published around 1999-2001. This is, of course, not medical advice and these judgments are up to clinicians able to make decisions based on a person's specific situation, the level of risk that's acceptable and the risk/benefit tradeoffs. I would keep your donor card, basically. (If I remember rightly, what the doctors did was take the people who'd received this person's organs off the immunosuppressant so that their immune system would learn to recognise the transplanted organ and cancer cells both as non-self.) Blythwood (talk) 23:08, 2 September 2021 (UTC)[reply]

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]

It's that electricity companies are in many countries obliged to supply electricity. They aren't allowed to go "eh, not worth it right now, we're making a loss" and just turn your power off. Negative prices are energy company 1 finding they have to keep a power station or a solar panel running when few people want the energy. More explanation here. Blythwood (talk) 22:35, 2 September 2021 (UTC)[reply]

Surely there are bitcoin miners camped around the power plants waiting for such moments ;). 2601:648:8202:350:0:0:0:2B99 (talk) 22:43, 2 September 2021 (UTC)[reply]

@Blythwood That explains why too much electricity is generated once in a while. Not why it's so hard to get rid of it when you produce too much and would actually pay to fix that problem. And yes, certainly a win-win situation for bitcoin miners :) Joepnl (talk) 23:00, 2 September 2021 (UTC)[reply]

Yes, I have to admit I'm not an electrical engineer so I'm not an expert on the physics. Ideally yes, as you say, you'd have something like pumped storage or molten salt storage. Blythwood (talk) 23:14, 2 September 2021 (UTC)[reply]

The situation in Australia is as you describe. I do not know why commercial wind or solar operators don't just switch off their systems when the price goes negative. They are proposing to start charging residential solar systems if they supply 'unwanted' electricity. Many unknowns. Here's an example, where in Vic the price had maxed out, yet Tasmanian operators were being charged for supplying electricity

Greglocock (talk) 00:29, 3 September 2021 (UTC)[reply]

Based on [1] (and a few other less complete sources that I found using the search "electricity negative spot prices"), the answer is that power transmission lines are so designed that excess power in one area might be impossible to transport onto another area (where potential "power sinks" would reside). I am also pretty sure that "bitcoin miners" (as well as more generally high-power consumers) need to run their "plant" more often than "whenever prices are negative" to break even on their capital expenditure; and they potentially have some cost and/or delay associated with switching the plant on or off.

From the generation side (same source), it is not feasible to turn off power plants at a short notice, and furthermore certain power sources (wind and solar?) receive subsidies based on how much they produce, so that they are OK with selling at negative prices as long as it is not too negative. In the source the subsidies are a flat sum per MWh, but a guaranteed price for residential producers would cause the same effect. Tigraan^{Click here for my talk page ("private" contact)} 08:44, 3 September 2021 (UTC)[reply]

The best large-scale method of storing surplus energy is pumped storage, where conventional hydroelectric power plants are used "in reverse". See List of pumped-storage hydroelectric power stations for where this is used on a global basis. The key aspect is the efficiency of the storage/re-use cycle. The OP's suggestion of melting steel would be a case where it was difficult to re-use the stored energy. Mike Turnbull (talk) 11:04, 3 September 2021 (UTC)[reply]

One of the problems with pumped storage hyrdo is that it is land-intensive and requires a particular geography. There's concerns that it won't scale with increasing energy demands on the system; that is the need for more storage will quickly outstrip our ability to build reservoirs to pump water into. Also, you actually need water for that to work, and in many places that have lots of sun and wind where pumped hydro storage is a good idea to stabilize renewable energy, they have major water problems. Look up a recent picture of Lake Mead for example. If you're going to tuck a pumped storage hydro plant somewhere in the Sierra Nevadas or something like that, where is the water going to come from? --Jayron 32 11:09, 3 September 2021 (UTC)[reply]

Electrical demand HAS TO equal electrical output. If there is excess electrical energy in the system, it has to go to another form of energy. If you don't have anywhere else for it to go, it becomes heat... and that heat does stuff like melt wires and other electrical equipment... bad times. You need to have other places for that excess energy to go. Batteries store the extra energy as chemical potential energy. Pumped-storage hydroelectricity stores that energy as gravitational potential energy. But excess electrical energy output HAS TO go somewhere, the first law of thermodynamics is a mean bitch like that. Energy must be conserved. So, if the electrical system doesn't have enough storage for your extra electricity that you want to generate, they need you to shut it down. They encourage that by charging you extra for the extra electricity you are making. Because if you keep making it, they have to find something to do with it, which costs them money. Most electrical systems are working on storage options and expanding capacity, but unless and until they get to the point where they can take your extra electricity, they don't want it. With many utilities, they will discount your electrical bill if you make your own solar, because your demand is still exceeding your production. However when large scale producers (i.e. not just you in your home) produce excess electricity, they aren't producing any demand. It's just a bunch of electricity from solar panels or turbines or something. They either have to shut down or pay the utility for storage. See this video from Physics Girl that explains both the infrastructure challenges and economics of this. --Jayron 32 11:09, 3 September 2021 (UTC)[reply]

One of the other storage methods becoming feasible where there aren't the facilities for pumped storage is battery technology. Remember Elon Musk's 100MWh installation in Australia?. It has been suggested, not entirely in jest, that when we all convert to electric cars, we can use their batteries for storage (keeping running costs down). Mike Turnbull (talk) 11:29, 3 September 2021 (UTC)[reply]

Battery technology presents its own challenges, especially with regards to materials and scalability as well. There is something to be said that batteries in vehicles (which are going to be used to drive anyways) represent a real source of electrical storage available to the system in the future, but large banks of idle batteries, which could represent a part of the storage solution, do not represent enough of a solution. The actual solution will likely involve a diversity of storage option, no one of which represents a significant portion of the total, but all of which are necessary. --Jayron 32 12:47, 3 September 2021 (UTC)[reply]

This problem of surplus energy is ongoing in the Orkney islands, which already generate up to 140% of their energy consumption with wind and tidal power, and could host the infrastructure to generate a lot more. However, they're constrained by the current (pun unavoidable) 40MW maximum capacity of their link with the mainland of Scotland (and Great Britain's National Grid, in turn linked to several other European counties' grids), as adding to this would be much more expensive than installing more wind and tide generators. The way forward may be to use the surplus to manufacture hydrogen from seawater, and export that.

It's explained more eloquently in this recent video on Tom Scott's YouTube channel. {The poster formerly known as 87.81.230.195} 2.122.0.2 (talk) 15:37, 3 September 2021 (UTC)[reply]

An excellent video I also considered linking when I linked Diana's video above. Thanks for that! --Jayron 32 15:42, 3 September 2021 (UTC)[reply]

Hurricane flood water

Where does most of the flooding from a hurricane come from? E.g. New York appears to be under 3 feet of water now, and of course Louisiana had it even worse. Is it ocean water that got swept in by the cyclone, or is it actually ultra powerful rain (i.e. evaporated water that recondensed)? Is it drinkable (like rain water)? Undrinkable because it's full of ocean salt? Or undrinkable pretty much everywhere (even filtered) because of contaminants on the ground getting into it? I'm in California under a drought, but I guess they can't send any of the hurricane water here regardless. Thanks. 2601:648:8202:350:0:0:0:2B99 (talk) 22:42, 2 September 2021 (UTC)[reply]

It comes down as rainwater, buy where it collects it is largely surface runoff and therefore contaminated with any filth you will find on the ground. --Lambiam 01:58, 3 September 2021 (UTC)[reply]

It can also be contaminated by sewage, since the normal sewer system (whether combined or not) will not be working properly. --184.144.99.72 (talk) 06:47, 3 September 2021 (UTC)[reply]

It depends, though there are typically two different sources of flooding in a hurricane:

Storm surge is water that is "pushed up" onto land from the ocean that is driven by the extreme low pressures and high winds of the hurricane. In coastal areas, such as where the storm makes landfall, much of the flooding is caused by storm surge rather than rain.
Rainfall itself can cause flooding, especially in areas where there is not a means to quickly dissipate the accumulating waters. In places like Philadelphia, for example, the Vine Street Expressway is an impermeable ditch that runs lower than the rest of the city. The massive amount of rain that fell (as quickly as 2-3 inches in one hour, over several hours) all finds the lowest point, which in that part of the city was the expressway, meaning that most of the rainwater ended up turning the expressway into a canal. The water filled the entire depressed roadway (5 meters or so of it) up to street level with water. Yes, there are storm drains, but these can only remove water so fast, they also get clogged with debris, and as a result, there's just no way for the water to drain fast enough. Look at images like [2] show the scope of the problem. Major cities like New York and Philadelphia have all of this sort of "artificial geography" that under these heavy rain conditions will just collect water, like depressed freeways or subway systems. That's why, even in an inland city like Philadelphia (or a well-protected coastal city like New York) you still get massive flooding; even if there was not a storm surge issue, you still get rainwater problems. --Jayron 32 18:10, 3 September 2021 (UTC)[reply]

The NY subway has always had water pumps (and they're still good enough almost 100% the time) but most of the system is 80-117 years old, the street drain system is old and anthropogenic rain rates are starting to obsolete them. The recent tropical depression (remnant?) smashed the Manhattan, Newark etc weather stations' hour records for rain, adjacent hours almost as bad, 2/3rds inches in 5 minutes (!) at a minor weather station and half inch in at most 5-6 minutes in most of the city, that overwhelmed or bypassed the pumps to the point that one stairwell became like the scene in Titanic where the waterfall breaks the doors. Sandy of course was the storm surge variant, where most of the sub-"river"bed tunnels (up to 100-150ft below sea level) became filled with saltwater cause the sea level became higher than the lowest air shaft, station entrance or emergency exit. Sagittarian Milky Way (talk) 20:38, 3 September 2021 (UTC)[reply]

(after edit conflict)

Storm surge, as described by NOAA, "is caused primarily by a storm’s winds pushing water onshore" and is distinct from actual rainfall, which is also distinct from precipitable water, and forecasted precipitable water; and all of these are distinct from runoff, which is often defined as the actual depth of water above ground.

Depending on where you are and what the weather is doing and what is has been doing historically, the volume of water above ground - in other words, "the water that's causing the flood" at a particular spot - can be primarily attributed to any of these causes (or others). One of the jobs of a hydrologist is to subjectively and quantitatively analyze where each component of floodwater comes from, and how to mitigate its hazards.

The New York office of the National Weather Service regularly publishes a Hydrology analysis as part of their area forecast discussion, a text-product that gets updated multiple times per day (and more frequently when weather emergencies call for it).

The US Geological Survey also has responsibility for some aspects of hydrology science. Here's the main website for the New York Water Center. USGS uses different but related methodology, compared to the National Weather Service, so it's interesting to see how two communities of scientists study the same issue in different ways.

Nimur (talk) 18:17, 3 September 2021 (UTC)[reply]

September 3

Plant questions.

What are some examples of underwater plants that can thrive in saltwater, and freshwater?

What are some examples of plants that can thrive in both basic pH soil, and acidic pH soil?

Is there a correlation? 67.165.185.178 (talk) 00:44, 3 September 2021 (UTC).[reply]

For salt and fresh water, see halophyte vs glycophyte. Don't know about pH. 2601:648:8202:350:0:0:0:2B99 (talk) 03:19, 3 September 2021 (UTC)[reply]

For lists of some aquatic plant species that thrive in sea water, brackish water and freshwater, see Category:Seagrass, Category:Brackish water plants and Category:Freshwater plants. --Lambiam 10:17, 3 September 2021 (UTC)[reply]

Soil_pH#Plant_pH_preferences has a table of examples (with tolerance ranges, because plants have varying degrees of fussiness). I'm not sure if this helps with your final question, given that these are land plants. The pH of the underwater soil that aquatic plants grow in ... is an obscure question. Card Zero (talk) 13:09, 3 September 2021 (UTC)[reply]

Extremophile also has some information on life forms that live in very high or very low pH. --Jayron 32 15:40, 3 September 2021 (UTC)[reply]

September 4

Why don't cyanide millipede curl like other millipedes when it got touched?

Why don't cyanide millipede curl like other millipedes when it got touched? Rizosome (talk) 04:31, 4 September 2021 (UTC)[reply]

Who says they don't? This indicates they curl up into a spiral and then exude cyanide. --jpgordon^{𝄢𝄆𝄐𝄇} 05:03, 4 September 2021 (UTC)[reply]

I read This understand it curl like other millipedes, but why it's called cyanide millipede instead of hydrogen cyanide millipede if it exude hydrogen cyanide to fight predators? Rizosome (talk) 06:10, 4 September 2021 (UTC)[reply]

Common names developed informally over time and are used only for convenience. They are not intended to be accurate descriptions, in fact they are often misleading.--Shantavira|^{feed me} 06:39, 4 September 2021 (UTC)[reply]

Also, the term cyanide can be used as a count noun (as in, “A cyanide is a chemical compound that contains the group C≡N”) or as a mass noun (as in “Cyanide is one of the most famous poisons”). When used as a mass noun to refer to a gas, the usual meaning is “hydrogen cyanide”. Compare the use of the term salt: sodium chlorate is a salt, but when a recipe requires “a pinch of salt“, this means sodium chloride and certainly not sodium chlorate. --Lambiam 07:24, 4 September 2021 (UTC)[reply]

Many millipedes exude HCN compounds when threatened. My giant African millipede Nigel would sometimes startle himself by accidentally stepping in our creek and would leave behind a nasty oil slick. He never sprayed me, though :) JoelleJay (talk) 17:14, 4 September 2021 (UTC)[reply]

Dental care

For a correct dental care, I should take before mouthwash or toothpaste? --94.247.8.8 (talk) 09:46, 4 September 2021 (UTC)[reply]

Were you told they contradict? 67.165.185.178 (talk) 11:18, 4 September 2021 (UTC).[reply]

You should ask your dentist that question. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:25, 4 September 2021 (UTC)[reply]

Can the existence of a soul be proved or disproved with science?

As a Christian, I believe that the body has a soul that is sent to heaven or hell after one's death. In short, can the existence of a soul be proved or disproved with science? Félix An (talk) 23:57, 4 September 2021 (UTC)[reply]

No. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:29, 5 September 2021 (UTC)[reply]

You will have to look at your definition of soul which can be a translation of ancient Greek psyche. You may wish to look at the work of Frank J. Tipler. But I think proof is outside science, and the study lies in Christian anthropology and philosophy. Graeme Bartlett (talk) 01:42, 5 September 2021 (UTC)[reply]

Science hasn't proven anything since 1959, when The Logic of Scientific Discovery pointed out that it doesn't really work that way and disproving things is all we can manage. Card Zero (talk) 02:01, 5 September 2021 (UTC)[reply]

Weird, the only churches that I know of that still teach about a literal Heaven are Black churches. Most White churches believe Heaven is just where God dwells, if you are "saved," you simply become part of God's memory. So it's not "do you go to Heaven or Hell," but "do you go to Hell, or not go to Hell." 67.165.185.178 (talk) 03:56, 5 September 2021 (UTC).[reply]

Huh? I have never heard of a Christian church, regardless of ethnic composition, that teaches that it is possible to retain consciousness after death, but only by going to Hell. That sounds like an especially grim teaching. Reminds me of an Ian Watson story or something. Where have you come across this? --Trovatore (talk) 16:42, 5 September 2021 (UTC)[reply]

If your concept of soul is that of an incorporeal entity, that is, having no material form and not being subject to the laws of physics, it follows that no scientific experiment can contribute to any judgement about the existence or properties of souls. If, however, you believe that souls are material and possess mass, you can attempt to measure it. --Lambiam 06:50, 5 September 2021 (UTC)[reply]

September 5

How much of Speed of light can be decreased until Universe go unstable?

I feel stability of universe also depends on speed of light. So how much of Speed of light can be decreased until Universe go unstable? Rizosome (talk) 02:56, 5 September 2021 (UTC)[reply]

Where did you get this idea from? Also note that the speed of light varies depending on what it's traveling through. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:23, 5 September 2021 (UTC)[reply]

The metre is defined in the International System of Units (SI) as the distance travelled by light in vacuum in 1/299792458th of a second. It follows that the speed of light is exactly 299792458 metres per second. If it goes down, this means that reciprocals have become unstable. --Lambiam 06:24, 5 September 2021 (UTC)[reply]

That's not a fact about the speed of light; it's a fact about how the meter is defined in SI. I think we have an article called variable speed of light; I haven't looked at it recently and don't know what it currently discusses, but you can't answer the question "what if the speed of light were lower" by talking about a particular system of units. (It would certainly be fair to ask the questioner what is meant.) --Trovatore (talk) 16:19, 5 September 2021 (UTC)[reply]

Let's not some of us lose sight of the fact that the value c, colloquially referred to as "the speed of light," is a fundamental physical constant (we think) which light or other massless entities in a vacuuum necessarily must travel at, but that's an imposition on light by the universe, not something imposed on the universe by light. That light or other massless things travel at different velocities when not in a vacuum has no relevance to questions like Rhizome's.

As to that question, our article Fine-tuned universe may be of interest, as might Fine-tuning. {The poster formerly known as 87.81.230.195} 2.122.0.2 (talk) 19:36, 5 September 2021 (UTC)[reply]

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

[1]