Several questions: (1) Can a Boeing 707-120B take off at MTOW from Runway 04/22 at Greater Rochester International Airport? (2) How much payload (if any) would have to be taken off for the same jet to take off from Runway 10/28 at the same airport, with a 45-knot headwind and below-freezing temperatures as would be the case in a severe blizzard (and would this be possible at all)? (3) How much payload (if any) would have to be taken off for said Dash-120B to fly nonstop from ROC to Rome Fiumicino Airport with acceptable reserve fuel remaining, assuming no tailwinds along the route (and would this be possible at all)? (Questions inspired by the original Airport movie.) 2601:646:8082:BA0:649B:7753:3C84:C70D (talk) 12:27, 22 June 2024 (UTC)
1: According to the official documentation from Boeing, if it's equipped with the original JT3D-1 engines, the takeoff runway length requirement at 500 feet above sea level, standard temperature and maximum take-off weight is 8500 feet. Those Boeing documents are in US units. Your runway is 8001 feet, so it won't fit. At least, not with the proper safety margin. If equipped with the more modern JT3D-3 engines, the takeoff runway length requirement is 7800 feet, so that fits.
2: Under normal circumstances, assuming JT3D-3 engines, maximum weight on a 6400 foot runway is 232,000 pounds, 26,000 pounds below MTOW. Freezing temperature would take the density altitude down to below sea level, which the documentation doesn't tell about, so I'll assume sea level. The 45 knot headwind reduces takeoff groundspeed to about 70% and required runway length to a bit more than 50% of the original, so about 4000 feet should be enough, even at MTOW. Unless there's snow on the runway. Ploughing through snow may increase drag enough that it can't take off at all, but it also reduces braking performance, so you need more length for an aborted takeoff.
3: The distance from ROC to Fiumicino is 3780 nautical miles. Taking off at MTOW, it can carry a payload of 25,000 pounds, assuming JT3D-3 engines and a standard cabin configuration. This is slightly less than a full payload of 137 passengers and baggage, 28,000 pounds. Maximum payload for short flights is 42,000 pounds, passengers, baggage and cargo. PiusImpavidus (talk) 09:54, 23 June 2024 (UTC)
Because I'm doing some very early work on a rescuesimulator game, so for this mission I wanted to move the departure airport further east so as to speed things up (it wouldn't do to have some of the players, in particular the one playing the medic, sit around for 2 hours or more doing nothing) -- but I see this probably won't work, so I guess I'll go with Boston Logan Airport instead (I had rejected it at first because I thought it would have sped things up too much, but on second thought it wouldn't be the case because the flight would be flying parallel to the shore at first). Not happening any time soon, though -- for one thing, a simulator would be way over my head at this point (and I'd have to put together a whole studio, because it's far too much work for just one person, no matter how highly skilled), and also for this particular mission I'd have to first get permission to use the likenesses of Dean Martin, Jacqueline Bisset, Helen Hayes and Van Heflin as Vernon Demerest, Gwen Meighen, Ada Quonsett and D.O. Guerrero respectively! 2601:646:8082:BA0:649B:7753:3C84:C70D (talk) 21:34, 23 June 2024 (UTC)
And there was me thinking you meant Rochester Airport, which is certainly further east. Alansplodge (talk) 14:56, 24 June 2024 (UTC)
I'll admit to having to read the original comment twice. The thought of a 707 attempting to take off from Rochester Airport's 2,000 feet (610 m) grass strip is a bit alarming! Martin of Sheffield (talk) 09:04, 25 June 2024 (UTC)
Hi. Some motor drivers have an energy saving feature; for example, in the TMC2209[1] it's called "CoolStep".
I'm guess that this is accomplished via some very clever control circuitry inside. For example:
1. if a stepper is holding its position, and there's 0 load on it (just a bare stepper motor sitting on a desk connected to a TMC2209), then 0 current is needed
2. if I use my finger to try to turn the stepper shaft, a back EMF is generated in the stepper. The TMC2209 senses this voltage, and supplies a current in the opposite direction to counteract it
3. as a result, my finger will feel a "torque" from the stepper, and the stepper will hold its position, despite my applied force
(This is my best understanding of how it works.)
Is it possible to apply this same technique, or an analogous technique, to drive a solenoid?
I'm asking because the two situation are almost analogous to each other:
A. a solenoid is connected to a solenoid driver. A permanent magnet is stuck to the solenoid via magnetic force. There is 0 movement, so 0 induced voltage. There is 0 force, so 0 current is needed to hold this position
B. if I use my finger to try to move the magnet, a back EMF is generated in the solenoid. The solenoid driver senses this voltage, and supplies a current in the opposite direction to counteract it
C. as a result, my finger will feel a "force" from the solenoid, and the magnet will hold its position, despite my applied force
Is this kind of control actually possible in reality? In my head, I'm imagining something like this is possible in theory, but I don't know enough electronics to know whether it's actually possible or not.
Is there any commercial solenoid driver that can accomplish the above described power-saving feature? I could not find any myself. Since manufacturers use different marketing terms (such as "CoolStep") to describe their proprietary technology, it's possible that such a driver exists, but I don't know the right keyword to search for so I cannot find it. OptoFidelty (talk) 21:24, 22 June 2024 (UTC)
The TMC2209 Datasheet says thatCoolStep's operation relates to the StallGuard4 feature, which it describes as being based on back-EMF. But "CoolStep is not able to measure the motor load in standstill and at very low RPM". One application of sensing linear motion and counteracting it (effect: holding something in approximate position with minimal required force) is damping...lots of ways of implementing it. DMacks (talk) 21:53, 22 June 2024 (UTC)
Is there any commercially available IC that can achieve this damping effect?
I'm guessing that there are at least a dozen solenoids any new car, so presumably they have some very smart solonoid drivers inside them to control the drive current.
Currently I'm just using a constant current to drive the solonoid, which is very wasteful, since 99% of the time, 0 current is needed. I don't know how to achieve this back-EMF sensing feature on my own.
It'd be helpful if I can find a commercially available solonoid drivers IC that has this feature built-in. OptoFidelty (talk) 22:48, 22 June 2024 (UTC)
Not my field (ha!), sorry. DMacks (talk) 02:39, 23 June 2024 (UTC)
No worries. Thank you for the help so far.
At least I know it's physically possible now. Just not sure where to find any commercial solutions for it, if such a thing exists. OptoFidelty (talk) 06:40, 23 June 2024 (UTC)
The back-EMF gives a velocity sensor. Holding a position with only a velocity sensor is possible with a perfect sensor, but in reality sensors aren't perfect and some creep will happen – which is why the example mentioned above doesn't work in standstill. You need a position sensor, or apply a brake. PiusImpavidus (talk) 10:17, 23 June 2024 (UTC)
I'm looking for useful physical formulas of the form:[edit]
Where the are physical properties of the same type (e.g. of energy, or of electric charge, and likewise).
Those physical properties don't have to be denoted by the same letter in the formula.
They should be denoted by not more than three letters, excluding indices if needed.
The indices: "total", "initial", "additional", mentioned above, don't have to be mentioned in the formula, either. They should be understood, though, from the standard meaning of the letters/indices mentioned in the formula. Therefore, formulas of the type should be ignored, because none of those Es (=energies) is usually interpreted as "initial".
What about integrations, eg the amount of electric charge on an object = integration over time of the current flowing through a surface that encloses the object.? (+ initial charge) Graeme Bartlett (talk) 11:21, 23 June 2024 (UTC)
I even avoid simpler formulas, e.g. of the type not to mention HOTmag (talk) 12:05, 23 June 2024 (UTC)
Your example uses too many letters. I must use three only (the Xs), and all of them should be of the same type, as indicated above. HOTmag (talk) 16:03, 23 June 2024 (UTC)
Why can YT offend me? Because it also means YouTube? HOTmag (talk) 06:59, 24 June 2024 (UTC)
"Where the are physical properties of the same type" - they have to be for the equation to make sense. see Dimensional Analysis. i can't off hand think of a non trivial equation that is simple enough for your requirements. weight_today=weight_yesterday+change_in_weight_per_day? Greglocock (talk) 22:16, 23 June 2024 (UTC)
They have to be [of the same type], for the equation to make sense: Yes, of course. I'd only wanted to exclude hypothetical examples meaning eg: "What I like to talk about = energy + electric charge". Admittedly, it's only a hypothetical example, because it does not reflect any useful formula, whereas what I need should be a useful formula, as indicated in the title. This requirement also excludes your last suggestion. HOTmag (talk) 06:59, 24 June 2024 (UTC)
Yes, this is a good example. Anything else? HOTmag (talk) 06:59, 24 June 2024 (UTC)
See equations under Equation_of_time#Mathematical_description such as "EOT = GHA - GMHA" and following. Also see and following at Post-Newtonian expansion. In general, this type of equation comes up when you're trying to split a difficult problem into a larger part, which can be exactly solved, and a smaller part, which can be treated as a perturbation. --Amble (talk) 17:10, 24 June 2024 (UTC)
Thank you. To me, the time formulas are better than the Post Newtonian expansions, because I need precise equations rather than approximations. HOTmag (talk) 18:20, 24 June 2024 (UTC)
Does it have to be symbolic, or does this count: "When the voltage is increased by 100 volts, the new voltage will be 150 V + 100 V = 250 V"[2]? --Lambiam 06:52, 24 June 2024 (UTC)
As indicated in the title, the example should be a useful formula, so yes it has to be symbolic. HOTmag (talk) 06:59, 24 June 2024 (UTC)
The color sequence of stars is that M stars are red, K=orange, G=yellow, F=yellowish white, A=white, B=bluish white, and O=blue. The sun is a G star. But I keep hearing that the sun is white. Does a correction need to be made?? is G really white (as opposed to A being white that we learn from this sequence)?? Georgia guy (talk) 01:43, 24 June 2024 (UTC)
See stellar classification, particularly the section on conventional colour description. The peak spectrum of the Sun is around yellow. As far as we are concerned using our eyes the Sun is white. As far as astronomers using instruments are concerned, it is slightly yellow. Hotter stars are comparatively bluer, and cooler stars are comparatively redder. Stars are so bright that each one at the same apparent luminosity will appear as a shade of white tinged with something else, at least for humans that evolved under the Sun's particular spectrum. What we call a "red" star, i.e. Betelgeuse, is only red by comparison - it's really kind of pink as far as we're concerned, and that's kind of an extreme example. Acroterion(talk) 01:51, 24 June 2024 (UTC)
The Sun is white because, almost per definition, white is the colour of the visible spectrum of the light emitted by our sun. Snow is white because it reflects this light uniformly. --Lambiam 05:51, 24 June 2024 (UTC)
Colour perception can be weird. Some observers see Beta Librae (Zubeneschamali) as green, even though that shouldn't be possible since green is in the middle of the visible spectrum. Double sharp (talk) 07:31, 24 June 2024 (UTC)
The sun is, to our eyes, white, more or less by definition. The white balance of our eyes automatically adjusts itself to the colour of ambient light and the sun provides most of our ambient light, making sunlight white.
Astronomers usually express colours in a number, not a word. You take the magnitude of an object as measured through a particular colour filter, do it again through a different filter and find the difference. Magnitudes are logarithmic, so this is the logarithm of the ratio of brightnesses in two wavelength bands. See colour index. Traditionally, magnitudes are calibrated such that the magnitude of Vega is zero in every band. That makes the colour index of Vega, an A0 star, zero. If you say that a colour index of zero means white, than Vega is white and the Sun is yellow. But as every photographer knows, there's no absolute truth in white balance.
Not all stars have a spectrum close to a black body. Strange colours do occur. PiusImpavidus (talk) 10:27, 24 June 2024 (UTC)
Interesting. Phil Plait explains Beta Librae along those lines in one column, noting that it is a young star and a rapid rotator. Double sharp (talk) 12:26, 24 June 2024 (UTC)
I haven't seen anyone mention that the reason we think of the Sun as "yellow" is that this is its color when it's low in the sky (but not low enough to be orange), and when it's higher than that, we can't (and definitely shouldn't) look at it for more than a split second. However if there's a bit of cloud cover that you can view the Sun through (at your own risk!) higher in the sky, you'll see it as white.
Now, to be honest, I don't have a source for that being the reason. But it does seem pretty obvious. --Trovatore (talk) 00:51, 25 June 2024 (UTC)
There's probably a discussion about that somewhere, but yes, the only time humans can safely examine the sun and assess its color, even for an instant, is when it's low on the horizon and yellow, orange, or red according to atmospheric conditions, and because we associate warm colors with, well, the warmth of the sun. There's also a lot of yellow sun cultural baggage that starts in preschool - ask a child to draw the sun and they'll reach for the yellow crayon. And as PiusImpavidus notes, white balance is what we decide it is."Daylight" light bulbs that mimic the sun's color temperature appear distinctly blue to humans used to orangey domestic lights. Acroterion(talk) 12:07, 26 June 2024 (UTC)
I mean, you probably shouldn't replicate this experiment, but FWIW, the midday sun looked white to me when I accidentally glanced at it. :) Double sharp (talk) 14:49, 26 June 2024 (UTC)
I heard that, although we usually think that Human intelligence (or at least human-like) is exclusive of humans, other species of hominids were also capable of it. The best known one, the Neanderthal. They are extinct, so human-like intelligence is exclusive of us now, but not in the history of evolution.
But which are, then, the specific species that developed such intelligence, as opposed to being just very smart animals? Hominidae is clearly not, as gorillas and chimpanzees are not in that level. Is it Homo? Is it Archaic humans? Are either of those composed only of intelligent creatures, excluding non-intelligent ones, or are they groups of related species regardless of intelligence? Cambalachero (talk) 02:51, 24 June 2024 (UTC)
Neanderthals are an archaic human species; Homo is a genus including modern and archaic humans. Intelligence is a concept that is very hard to define. Human intelligence arose in a long process of evolution; it is impossible to point out a specific point where the intelligence of our progenitors became "human", both because this did not leave a traceable paleoanthropological record and – more importantly – because it is not possible to define the boundary between "pre-human intelligence" and "human intelligence". For the little that is known, see Evolution of human intelligence. --Lambiam 04:30, 24 June 2024 (UTC)
I have seen conflicting claims about whether the domestic cat descends from the European Wildcat or from the African Wildcat. Cat#Evolution shows two phylogenies: one (based on analysis of nuclear DNA) which shows the domestic cat being most closely related to the European Wildcat (and the Domestic/European Wildcat group being a sister group of the African Wildcat/Chinese Mountain Cat). The other (based on mitochondrial DNA) shows the domestic cat being descended from the African Wildcat. What does this actually mean? Is it just a case of "data from different sources is contradictory and we haven't got a conclusive answer yet"? Or does it mean that domestic cats are descended from male European wildcats that mated with African females? Or something else? Iapetus (talk) 12:07, 24 June 2024 (UTC)
Well mitochondrial DNA is inherited from the mother, so it means that the mother of the mother of the mother of the mother of the mother of the mother ..... of a domestic cat is an African wildcat. Many other ancestors could be European wildcats. Can these two kinds of wild cat interbreed? Graeme Bartlett (talk) 22:48, 24 June 2024 (UTC)
Both phylogenies can be brought into agreement in the following scenario. African wild cats were domesticated. It seems plausible that cats were first domesticated in Egypt or thereabouts. These domesticated African cats were brought to Europe and interbred with wild European cats. When a male domestic cat interbred with a female wild cat, the hybrid offspring was born in the wild and, being hybrid, was not so likely to survive, keeping the European wild cat distinct from the African wild cat. When a female domestic cat interbred with a male wild cat, the hybrid offspring was born in captivity and likely to survive as a domestic cat, making the European domestic cat evolve towards the European wild cat, whilst keeping the African mitochondrial DNA.
There's also selection pressure on domestic cats, keeping them distinct from European wild cats. PiusImpavidus (talk) 11:25, 25 June 2024 (UTC)
However, in the UK (where latterly the species has only survived in Scotland) the population of Scottish wildcats has significantly hybridised with domestic cats. Active breeding and re-introduction programs are taking place to counter this. (The poster foremrly known as 87.81.230.195} 151.227.226.178 (talk) 16:08, 25 June 2024 (UTC)
I have a bottle of 50 ml with cypermethrin. The instructions by the manufacturer say diluire al 2-3% in acqua. Do they mean I must dilute it to a 2% to 3% solution (for example mix with 2 liters of water which will give a 2.4% to 2.5% solution)? Thank you. Hevesli (talk) 17:24, 24 June 2024 (UTC)
Yes you could do it that way. But if you don't want to use 2 litres of solution you could mix less, say half of it in 1 liter or 1 ml in 50 ml of water. Graeme Bartlett (talk) 22:51, 24 June 2024 (UTC)
Is the sun upside down in the Southern Hemisphere[edit]
appearance of moon at moonrise
I have heard that the moon is upside down in Australia but I don't know if the sun is also upside down in Australia. Can anyone tell me because I am curious. 2001:8003:429D:4100:20F0:744E:F9F2:D791 (talk) 23:10, 24 June 2024 (UTC)
If you check out the angle of the person on the Earth, say from someone at 45° north going to someone 45° south, the difference is 90°, so the appearance is sideways on. But from north pole to south pole it is rotated a full 180°. But at the poles it will be hard to see the sun from both at the same time. With the Sun it is harder to see it is rotated or not, as normally you won't be able to see any detail on the sun. With sunspots your could see something with the right equipment. But not only movement around the Earth will rotate the view of the sky, looking at moonrise and moonset will see that the moon has rotated in the sky for you. The same will apply to the Sun. Graeme Bartlett (talk) 23:51, 24 June 2024 (UTC)
Twice per year on the Equinox the Sun can be seen on the horizon simultaneously from both the North and South poles. Philvoids (talk) 17:54, 25 June 2024 (UTC)
Above the horizon as the centers will be 8 to 9 angular seconds below the horizon (parallax) but mean upward refraction is 34 angular minutes at the horizon it'd have to be less than half Earth average refraction for the circa 16 angular minute tall lower half to not clear the horizon. If the horizon isn't flat perhaps from icebergs it would be harder. Sagittarian Milky Way (talk) 22:17, 25 June 2024 (UTC)
Regarding the moon being "upside down", it depends how you're standing when you're looking up at it. The natural thing to do is to look up at the narrower angle. But if you turn around (and have something to lean back on or are very well balanced), you can look up at it at a wider angle, and it will appear the way someone in the opposite hemisphere would normally look up at it. And I would think the same would apply to the sun. ←Baseball BugsWhat's up, Doc?carrots→ 00:37, 25 June 2024 (UTC)
When somebody is looking south at some object in the sky from Japan, and somebody else is looking north at the same object from Australia, the object will appear upside down for the person from Australia, because that person is upside down compared to the one in Japan. It doesn't matter what you're looking at: Moon, Sun, constellations, planets, alien spaceships... PiusImpavidus (talk) 11:36, 25 June 2024 (UTC)
Neither person is "upside-down" compared to the other. Tokyo, for instance, is about 7,800 km from Sydney. That's just under 1/5 of the Earth's circumference, so the two people are oriented about 72° apart, not 180°. --142.112.148.225 (talk) 19:08, 25 June 2024 (UTC)
This is bullshit. At sunrise or sunset on an equinox it's about 72° Sydney latitude vs Tokyo latitude same longitude but at noon on a sundial all other places same longitude will be 180° so long as the Sun's declination is between the 2 places. If the 2 latitudes are above 23.44 and below minus 23.44 respectively the Sun's declination will always be in between from now till over 10,000 years from now. Sagittarian Milky Way (talk) 22:35, 25 June 2024 (UTC)
Projected onto the plane perpendicular to the line Earth–Sun, one is upside down relative to the other. It's fair to make this projection, because either observer projects the orientation of the Sun onto his own vertical. PiusImpavidus (talk) 07:49, 26 June 2024 (UTC)
The image I put up here (not to scale) should make this somewhat intuitive. Imagine that the sunspots happen to make a face, so that an observer sticking their head up at the North Pole sees it "upside up". Clearly, an observer peeking out from the South Pole will then see it upside down. --Lambiam 12:49, 25 June 2024 (UTC)
That's very helpful; thank you. I've long known of the phenomenon, but always struggled to picture it. Matt Deres (talk) 17:33, 26 June 2024 (UTC)
I'm looking for examples of "irregular" light, i.e. light carryiing "irregular" quantities of physical properties.[edit]
Such as light carrying an infinite wavelength, i.e. zero-frequency, i.e. zero-momentum, i.e zero-energy, and the like. For the time being, I'd like to ignore the property of velocity.
Is there any evidence of such irregular properties of any light? If no evidence, then what about any theory mentioning this kind of irregular properties of light, as a hypothetically possible option? Maybe when light unsuccessfully tries to escape a black hole? HOTmag (talk) 00:32, 25 June 2024 (UTC)
Thank you. Do your examples include information about light carrying an infinite wavelength, i.e. a zero-amplitude, i.e. a zero-frequency? Please see my thread below. HOTmag (talk) 10:38, 25 June 2024 (UTC)
If zero-energy photons (or any zero-energy particles) exist, there is no way to detect them. If you think of particles as being an excited state of a quantum field, zero-energy particles are obviously not excited, so they are in fact not real particles. --Lambiam 10:28, 25 June 2024 (UTC)
Technically speaking, you are right. But please see my thread below. HOTmag (talk) 10:38, 25 June 2024 (UTC)
infinite wavelength, zero-amplitude, zero-frequency, and the like.[edit]
Every process involving charged particles emits infinitely many coherent photons of infinite wavelength, and the amplitude for emitting any finite number of photons is zero.
Do those hypothetical photons of infinite wavelength, i.e. of zero-amplitude, i.e. of zero-frequency, have a name? Is there any article where I can read about them? HOTmag (talk) 10:35, 25 June 2024 (UTC)
The adjective evanescent describes an oscillating electric or magnetic field that propagates as an electromagnetic wave but has its energy spatially bound in the vicinity of its source. Philvoids (talk) 11:55, 26 June 2024 (UTC)
For example, at the Pourbaix diagram beside, there is a borderline between Fe3+ and FeO2−4. Can a solution at that border be considered a solution of [Fe3+]2[FeO2−4]3, and if yes, can this salt be isolated?
More generally, if a cation and an anion touch in a Pourbaix diagram, do they form a salt? Nucleus hydro elemon (talk) 11:17, 25 June 2024 (UTC)
In this case it could not be the compound you suggest, as ferric oxide in itself is not alkaline enough to make the ferrate. So there would have to be some extra alkali around. On the line it could be either of the species from 0% to 100% and not necessarily in a 3:2 ratio to balance the charge. The charge is balanced by something like Na+ ions. In general it may be balanced by ions derived from water OH− or H+. Graeme Bartlett (talk) 11:56, 25 June 2024 (UTC)
I'm looking for an accepted or common term, for a free photon that hasn't been absorbed by matter yet.[edit]
Admittedly, I know I could simply say "photon" without adjectives, because if it had already been absorbed then it would no longer be a photon, but I still wonder if there's any direct adjective expressing more precisely the very fact - that this photon is still free - in the above sense. I think the term "free" photon is not sufficient. Maybe "unabsorbed" photon? HOTmag (talk) 16:05, 25 June 2024 (UTC)
@Philvoids:Yes, I know that, but how does it answer my question? Have I ever claimed bosons and fermions belong to the same category? I asked about photons only, rather than about their whole category. HOTmag (talk) 19:43, 25 June 2024 (UTC)
You can say "propagating photon". Ruslik_Zero 20:17, 25 June 2024 (UTC)
You could say "existing photon" (versus a no-longer-existing photon or a not-yet-emitted photon), but really, as you admit yourself, there's no need for such an adjective, so no such adjective is in common use. PiusImpavidus (talk) 07:59, 26 June 2024 (UTC)
So, I ran out of lime juice (containing citric acid) while cooking some fish, and started wondering if there were any easily obtainable/ common substitutes. Obviously vinegar (containing acetic acid) goes with fish, but it probably doesn't go with vodka and diet coke to reduce the sweetness (I haven't actually tried that yet). So I wondered how chemically similar citric and acetic acids are. I have a very basic knowledge of chemistry, (I scraped a C at O-level many moons ago), so please treat me as an interested layman whose lack of even fundamental mathematics at the time sadly prevented me from becoming an organic chemist.
Anyway, I started off with organic acids, where the lede lists some common carboxylic acids, but they don't seem to be in any sort of order.
(Answer, I think: Citric and acetic acids are somewhat alike, but only up to a point, Lord Copper). With some further hunting, I wondered about arranging the above list in order of complexity, with some extra additions: I hope I have got everything right. This exercise gave rise to some questions, included in the entries: I wonder if anyone could help me with these, please?
Carboxylic acids (one carboxyl COOH group)
Formic acid CH2O2 (Question 1: why is it not written HCOOH like oxalic acid below?)
Glycolic acid C2H4O3 (not in list) (Question 2: The list in Omega hydroxy acid#List includes it as matches the formula pattern CnH2nO3. To which classes does this pattern refer, like the alkanes match CnH2n+2?)
Isocitric acid C6H8O7 (not in list)- (Question 4: How can it be both a tricarboxylic and an Alpha hydroxycarboxylic acid? Is one a subset of the other?)
(Question 6: How many of these groups in main bullet points match a formula pattern like CnH2nO3?)
Thanks for your patience, cheers, >MinorProphet (talk) 12:49, 26 June 2024 (UTC)
Food-grade lactic acid and tartaric acid are used to give a sour taste to foods and drinks, so they are clear candidates for being tried as substitutes. If you happen to have unripe grapes or plums, you could use their juices. --Lambiam 16:28, 26 June 2024 (UTC)
Malic acid gives the tart taste to plums and many other fruits, as well as rhubarb. --Lambiam 09:37, 27 June 2024 (UTC)
Acetic acid has a strong odour, and so will change the human experience. Many of the acids you listed above are toxic and so either should be avoided or only used in tiny amounts as they occur in foods, eg oxalic acid. Q1: Formic acid can be written written HCOOH. Q2: the pattern you give is for an alkane derive carboxylic acid with extra oxygen. An extra oxygen could go in between carbon and hydrogen so that it is a hydroxy acid, (alpha, beta, omega etc); it could form an ether between two carbons, or it could go next to another oxygen and make a peroxy acid. The alkane base compound could be a linear chain of carbon atoms, or it could be branched. Q3: compounds could be in more than one category, so that if the second carbon is the last, an alpha acid is an omega acid too. Q2: many of these compounds' formulae have been written using Hill notation, which has C first and H second then in alphabetical order. The formula you gave for oxalic acid is not in this form. However it does not matter as there is only one isomer with this combination of atoms. Often the formula can be written in a variety of ways for one compound. Q4: a compound can be in more than one class if it meets the membership requirements or multiple classes. Q5: some compounds are acidic even if they are not carboxylic acids. Folic acid is a dicarboxylic acid. Uric acid can form a tautomer that can lose an H+ to make urate. It is not a carboxylic acid. And yes, both of these are heterocylcic compounds. Graeme Bartlett (talk) 22:58, 26 June 2024 (UTC)
Strictly speaking, other isomers of oxalic acid are possible. See C2H2O4search at ChemSpider which gives two others that have associated literature. Our organic acid article is very poor, probably because it is difficult to cover such a broad subject well. If the OP wants to delve deeper, a textbook would be a better place to look. We have recently started to link some on our Project Page at WP:CHEM#Good open access sources and the McMurry one has extensive coverage of organic acids. Mike Turnbull (talk) 13:20, 27 June 2024 (UTC)
Those general formulae above will actually have many more isomers by moving the oxygen or double bond around. But they would not be carboxlic acids any more. Graeme Bartlett (talk) 00:26, 28 June 2024 (UTC)
That's really helpful, thanks all very much indeed for some clear explanations. @Lambiam: would a bit of Cream of Tartar (in the kitchen cupboard) work? Not worried about the possible cloudy effect. @Graeme Bartlett: I wasn't thinking of trying all the acids I listed as lime juice substitutes, I was just hoping to make sense of the list in the Organic acid article. @Mike Turnbull: I found McMurry is also available at archive.org to borrow. Lots to think about. Exits left, clutching tripod, gauze mat, Liebig condenser and Bunsen burner. Favourite quote: Frederick Sanger described himself as "just a chap who messed about in a lab." MinorProphet (talk) 21:07, 28 June 2024 (UTC)
@MinorProphet That archive.org version is the fifth edition. The latest (10th) edition is the one available at Openstax. You can download .pdf by chapter or get the whole ~190 MB. Mike Turnbull (talk) 21:22, 28 June 2024 (UTC)
Here it is said that the tangy flavor of cream of tartar makes it an excellent addition to marinades, adding acidity and enhancing the taste of grilled or roasted meats. Whether it works in a fish recipe can only be determined experimentally. --Lambiam 09:57, 29 June 2024 (UTC)
And all this time I've been thinking that Tartar sauce contains some cream of tartar ... Abductive (reasoning) 05:55, 30 June 2024 (UTC)
1. Why are these maximally symmetric ones "unnatural" but there are major biology omega-3's/6's that start the divinylmethane pattern as little as 1 carbon higher? all-cis-3,6,9-dodecatrienoic acid
all-cis-3,6,9,12,15-octadecapentaenoic acid
all-cis-3,6,9,12,15,18,21-tetracosaheptaenoic acid.
2. Why does the article stop at hexaenoic? If there's 22:6 shouldn't there be room for 26:7?
3. Would all-cis-2,4,6,8,10-dodecapentaenoic acid melt at lower temperature than all-cis-3,6,9-dodecatrienoic acid, all-cis-2,4,6,8,10,12,14,16-octadecaoctaenoic acid melt at lower temperature than all-cis-3,6,9,12,15-octadecapentaenoic acid and so on? Sagittarian Milky Way (talk) 00:18, 27 June 2024 (UTC)
Slightly off-point but readers may like to know that you can do substructure searches over Wikipedia chemistry articles using Wikipedia Chemical Structure Explorer. It takes a bit of getting used to but allows, for example, searching for all divinylmethanes we have articles about. Similar searches can be run at PubChem with, of course, many more hits likely. PubChem will link the hits back to Wikidata if there is an entry here (possibly not an article or one not in English). Mike Turnbull (talk) 13:38, 27 June 2024 (UTC)
According to that there's no ringless unbranched acid on Wikipedia with a double bond at 3, the closest is the very important DHA 22:6 with double bonds at 4, 7, 10, 13, 16 and 19. Sagittarian Milky Way (talk) 18:45, 27 June 2024 (UTC)
If we forget about the muon's half-life, what would matter made from muonic atoms actually be like, in terms of physical and chemical properties?
(Yes, I know this is about as realistic as all those predictions of the chemical and physical properties of things like oganesson. But since there are published papers about that, maybe someone has considered this?) Double sharp (talk) 04:00, 27 June 2024 (UTC)
In Muonic atoms you can see that adding one muon instead of an electron in an atom makes it like the element with a one lower atomic number. But if all electrons were replaced with muons, then it would behave like a tiny atom. So then you could expect the materials formed to be much denser. 8,000,000 times denser. Also I would expect chemical bonds to be much, much stronger, and may be capable of making the material dense enough to initiate atomic fusion: (Muon-catalyzed fusion). With much stronger bonds, melting points of covalent network solids would be much higher. However I might expect similar molecular structures, but on a much smaller scale. Graeme Bartlett (talk) 12:05, 27 June 2024 (UTC)
In muonic atoms and molecules it is important to account for the QED corrections properly. They are much bigger than those in electronic atoms and molecules. Ruslik_Zero 20:30, 27 June 2024 (UTC)
Interesting. Muon-catalysed fusion does seem to be the show-stopper for this idea, since that makes it likely that a tank of muonic H2 (if we magically turn off the decay of the muons) would undergo significant spontaneous fusion. And the same thing would likely hold in general. So, even if the muon magically didn't decay, matter using it to replace all electrons would likely not be that stable either. :(
Thanks for the answers! Double sharp (talk) 13:11, 1 July 2024 (UTC)
Moved here from the Miscellaneous section of the Reference desk. --Lambiam 15:42, 28 June 2024 (UTC)
Time as we know it started with the Big Bang and following the Big Bang the universe continues to expand at an accelerating rate. Additionally based on the astrophysical presumption that the expansion of the universe will cease to accelerate and will lead to what astrophysicists are calling “the big crunch” whereby the universe will start to retract back to a point of singularity leading to repeated Big Bang events; my question is that if the universe was started to retract would time started to flow backwards? 149.12.2.131 (talk) 13:15, 28 June 2024 (UTC)
No, even if the Big Crunch were the fate of the universe. Entropy only goes one way. Supernovae won't reassemble themselves. People will not start sdrawkcab gniklat. Clarityfiend (talk) 13:44, 28 June 2024 (UTC)
If the arrow of time reverses, so does the direction of the increase of entropy. There is nothing per se contradictory with a model of the universe with a timelike parameter such that its entropy increases monotonically with for and decreases monotonically with for On one side of the arrow of time points in the positive direction and on the other side it points in the negstive direction – towards
The picture is complicated by quantum physics. The von Neumann entropy, which may be a more fundamental measure, should be invariant for a closed system. The universe as a whole is a closed system. The fact that we observe increasing entropy may be due to our inability to access the information that is "somewhere". As Special Agent Mulder would say, "the truth is out there". --Lambiam 17:01, 28 June 2024 (UTC)
So, the consensus is that we have to wait and see? DOR (ex-HK) (talk) 21:25, 28 June 2024 (UTC)
There have been and are many theories about the end of the universe. Given our present understanding of cosmology, the observations do not yet allow us to settle on a single one. We may need to keep observing for a couple of trillions of years. I don't think it can be definitely ruled out that the universe is an ergodic system that happens to be in a very low state of entropy. If it is, the Poincaré recurrence theorem promises us an eternal return.[3] --Lambiam 08:50, 29 June 2024 (UTC)
[T]he finer details of what goes on during this mating season are largely unknown due to the difficulties of observing the animals in their natural habitat, which is covered in dense ice that has just a few percent of open water [...and] researchers have yet to identify any noises specific to mating or courtship [...]
Then that means the article is comprehensive, since we already mention the tusk stuff under description. WolverineXI(talk to me) 21:31, 29 June 2024 (UTC)
OK, it's getting close to that time again when I have to clean my dryer duct (which requires me to move my gas-powered dryer away from the wall, disconnect the duct, install a mesh guard and reconnect the duct prior to cleaning the duct from the outside in while running the dryer to blow the lint out (mostly all over my face and clothes until I end up looking like Dick Van Dyke the chimney sweep in the film Mary Poppins), and then perform the same operation in reverse and push the thing back into its normal position after completing the cleaning). Last time I did this, though, it caused a big problem: pulling the dryer out from the wall went without a hitch, and for the most part so did the cleaning (except that I got all dirty like I already said above, and I got blisters and cuts on my hands from forcing the brush in, because the lint was hard-packed in places) -- but when I pushed the dryer back in, the fitting connecting it to the (supposedly flexible) gas hose "popped" in a way I've never seen before (and hope to never see again), completely disconnecting the hose from the dryer, and causing gas to start pouring in full blast from the still-open hose (fortunately I managed to shut off the main gas valve before the gas could reach its lower ignition limit, or this could have been a real disaster!) So, for next time, are there any tips for me how to pull the dryer out and push it back in without risking this happening again? 2601:646:8082:BA0:DC11:A4D3:D067:7B8E (talk) 23:37, 29 June 2024 (UTC)
Have you considered hiring a professional? Sometimes saving money can be expensive. --136.54.106.120 (talk) 00:27, 30 June 2024 (UTC)
This is a reference desk, not an instruction guide. In any case you should not take advice on maintaining gas appliances from random people on the internet. Get a professional to do it. Shantavira|feed me 08:59, 30 June 2024 (UTC)
I'd expect a shut-off valve between the fixed pipe coming out of the wall and the supposedly flexible hose connecting it to the the dryer (there was one for the gas hob where I used to live; I now live gas free), but if there's none, there's only the main gas valve. I suggest closing it before moving the dryer, just to be sure. PiusImpavidus (talk) 09:14, 30 June 2024 (UTC)
Yes, there is indeed a shut-off valve for the dryer, which I will consider closing before moving the thing (hopefully it will run in "air fluff" mode even with the gas shut off?) My question, though, was about how to move the appliance in such a way as to avoid the risk of rupturing the gas connection??? 2601:646:8082:BA0:DC11:A4D3:D067:7B8E (talk) 23:28, 30 June 2024 (UTC)
You obtain from the hardware store these little discs called "furniture sliders", some are felt and some are hard plastic, and put them under the feet of the dryer. Have a potato ready to jam in the gas line should it rupture. Abductive (reasoning) 06:40, 1 July 2024 (UTC)
Thanks! Or maybe I'll put a rug under it, and use that to pull it out and back in -- would that help reduce the risk of rupture? And maybe I'll pull out the washing machine as well, to make it easier to reach the valve in case the hose lets go again! 2601:646:8082:BA0:DC11:A4D3:D067:7B8E (talk) 21:49, 1 July 2024 (UTC)
My guess is that the hose was already halfway off after the first part of the procedure (moving the dryer away from the wall); being unaware of the risk of it slipping off you didn't notice it. Was the hose secured to the fitting with a tight hose clamp? This reduces the risk of accidental unintended disconnection. --Lambiam 08:50, 1 July 2024 (UTC)
No, it was not secured, and it still isn't (the person who installed the new hose didn't bother with a clamp) -- I'll make sure to fix that before attempting to clean the duct! Also, FYI, the old hose was at least 10 years old (and probably at least a couple years older than that -- God knows how long the previous owners lived in my house before I bought it from them, and from all the signs they didn't bother to do any maintenance to any of the appliances, they didn't even bother to flush the water heater, whereas I flush it every fall) -- so I think corrosion might have been a factor too! 2601:646:8082:BA0:DC11:A4D3:D067:7B8E (talk) 21:49, 1 July 2024 (UTC)
Everywhere I've seen in the US, the "gas connector"--the segment of gas-line from the permanent house infrastructure (near appliance shut-off valve) and the appliance itself is flexible metal with flared threaded connectors, or occasionally rigid metal like the house piping itself. I haven't seen anything that would have a hose clamp in decades. There is an older vs newer style of flexible metal tubing, with the newer ones (CSST: "corrugated stainless steel tubing") apparently designed to overcome how easily the older ones broke (older ones do not meet current code if I recall). So first order of business is make sure what you now have is up to code as far as type of connector and material. I'm not a plumber though, so best to check with one, or at least read product literature carefully at your local supply store. DMacks (talk) 16:07, 2 July 2024 (UTC)
Right -- and to clarify, last time it was actually the connector (presumably of the flared threaded type as you describe) which "popped", i.e. separated circumferentially into 2 unequal parts, thereby completely disconnecting the tubing from the appliance -- not the tubing itself! (Which is why I think corrosion probably played a part -- there's no way I can see such a fitting doing this unless the threads were rusted through, and with the thing having spent well over 10 years exposed to high humidity, car exhaust, chemicals, etc., this does sound plausible!) 2601:646:8082:BA0:DC11:A4D3:D067:7B8E (talk) 23:51, 2 July 2024 (UTC)
There are a gazillion instructional videos on youtube about stuff like this, if it helps. I've used them to fix various issues on cars, computers, and more recently a washing machine. Anyway, this is Wikipedia and I like to think that taking knowledge into our own hands (with some common sense precautions) is a good thing. 2601:644:8501:AAF0:0:0:0:9BB0 (talk) 03:23, 6 July 2024 (UTC)
Where does USA show its non-lawsuit certified 30yr station pressure averages?[edit]
I know at least 1 free commercial site lets you find hourly pressure since long enough ago but 30yrs would be manually averaging many thousands of numbers on 10,958 webpages one per day. I just want the regular $0 version not the paid certificated version for lawyers, bridge engineers etc Sagittarian Milky Way (talk) 15:26, 30 June 2024 (UTC)
By "station" do you mean "weather station" and by "pressure" do you mean "atmospheric pressure"? (If so, I don't know the answer, but I was struggling to understand the question, so perhaps others were also.)
Is the mention of bridge engineers pertinent to your reason for asking, or an inadvertent red herring? 151.227.226.178 (talk) 09:57, 1 July 2024 (UTC)
Weather station, atmospheric pressure. On one of the government weather/climate websites I saw a link to certified super-duper extra-checked data intended for lawsuits etc but presumably anyone can pay. Sagittarian Milky Way (talk) 12:50, 1 July 2024 (UTC)
And a specific weather station, not all of them averaged together (the only weather textbook I was lucky enough to have read (an undergraduate weather 101-level covering all meteorology) just called them stations) Sagittarian Milky Way (talk) 13:00, 1 July 2024 (UTC)
Is there any difference between, what "no rest-mass" means, and what "zero rest-mass" means?[edit]
1. Some authors write "light has no rest-mass", whereas others write "light has zero rest-mass".
2. There are some arguments against ascribing any rest-mass, even a zero rest-mass, to the light, e.g.
First, The formula of relativistic momentum may collapse once any value, including any zero value, is substituted for the rest-mass in that formula.
Second, light cannot be at rest, hence - logically - it cannot carry any rest-mass. That said, and bearing in mind - that although (for example) the function has no value at this does not mean that the value of the function at is zero - and more generally: when we don't ascribe "any value" to a property we don't mean the value of the property is zero, the same must be true for what we (don't) mean by "light has no rest-mass".
Third, from a logical point of view: Any sentence, whether true or flase, may be substituted for A in the true sentence "If light is at rest then A". Hence, for any value X, we will always get it right saying "If light is at rest then its mass will then be X". Hence for any value X, we will always get it right saying "if light has a rest mass then its value is X". Hence we would collide with a contradiction, if we assumed light carried any rest mass - even a zero one only.
3. On the other hand, there is a well known argument in favor of ascribing a zero rest-mass, to the light: This is actually a direct consequence, of combining the formulas , and
4. To sum up: Bearing in mind the pros and cons for/against ascribing a zero rest-mass to the light, I wonder if light, has no rest-mass at all, even not a zero rest-mass, or it still has a zero rest-mass.
To me, this relates more to semantics than physics. "Zero rest-mass" implies a countable quantity, as if it could be measured; "no rest-mass" suggests that rest-mass is not necessarily measurable. My understanding (based on knowledge from c.1980s) is that photons do not have a defined mass in a stationary state; and, "zero" is useful as a construct. --136.54.106.120 (talk) 18:02, 30 June 2024 (UTC)
As to your last word: I suspect zero can't be a construct. For more details, see my previous response, in its section 2, against ascribing any rest mass to the light, even a zero rest mass only. HOTmag (talk) 10:43, 1 July 2024 (UTC)
I was thinking of the noun "construct" referring to using "zero" as a logical placeholder for the absence of anything, nonexistence or "nothing" -- rather than a cardinal number. --136.54.106.120 (talk) 17:58, 1 July 2024 (UTC)
See my first response. Its section 3 gives an argument for ascribing a zero rest-mass to the light, zero being a cardinal number. On the other hand: section 2 gives three arguments against ascribing any rest mass - including a zero rest-mass - to the light, zero being a cardinal number. That's why I asked my question indicated in section 4. HOTmag (talk) 18:34, 1 July 2024 (UTC)
The concept of "zero" overlaps mathematics and philosophy. One could say that there are varying forms of nonexistence (?) — Preceding unsigned comment added by 136.54.106.120 (talk) 18:53, 1 July 2024 (UTC)
It seems you didn't get my point. I'm focusing on the contradiction between section 2 and section 3, both referring to zero as a cardinal number. The implicit question was: Can anyone remove the contradiction? HOTmag (talk) 20:32, 1 July 2024 (UTC)
A. Re. your first source: It claims light has a non-zero rest mass.
B. Re. your second source: Why didn't you provide also my section 3 as an additional "theoretical support for zero rest mass?"
C. However, please notice my section 3 contradicts my section 2. Also your second source contradicts my section 2. The implicit question was: Can anyone remove the contradiction?
D. Re. your last sentence. From a logical point of view, saying that "a photon at rest is a non-entity", is the same as saying that "light cannot be at rest". So, not only do I know that a photon at rest is a non-entity, i.e that light cannot be at rest, I also use this fact for establishing my section 2 (in its "Second" and "Third" paragraphs).
The real numbers are a field, which implies it has both an additive and a multiplicative identity, traditionally denoted by 0 and 1. These elements are true real numbers, not cardinal numbers.
There is a traditional embedding of the finitecardinal numbers in the real numbers which sends the cardinal number 0 to the real number 0 and the cardinal number 1 to the real number 1, but this fact does not turn these real numbers into cardinal numbers.
Since 0 kg = 0 μg = 0 oz = 0 Da, there is no need to specify the unit; "zero mass" is unambiguous. --Lambiam 23:43, 1 July 2024 (UTC)
As to cardinal numbers: Please notice I hadn't been the first to claim that zero was a "cardinal number". The anonymous user I responded to had, and I only followed them, adopting the term "cardinal number" they had already used, so your response should have responded to them rather than to me.
As to your last sentence: Did anyone claim there was a need to specify the unit? I only claimed there was a contradiction between sections 2,3 in my first post, and I asked if anyone could remove the contradiction. If you think there is anything wrong in my arguments in section 2 against attributing a zero rest-mass to a photon, please specify - both the wrong argument - and what's wrong in it. HOTmag (talk) 11:37, 2 July 2024 (UTC)
A) First source: I only read the abstract and noted This review attempts to assess the status of our current knowledge and understanding of the photon rest mass, with particular emphasis on a discussion of the various experimental methods that have been used to set upper limits on it. [And, yet]: failure to find a finite photon mass in any one experiment or class of experiments is not proof that it is identically zero and, even as the experimental limits move more closely towards the fundamental bounds of measurement uncertainty, new conceptual approaches to the task continue to appear.
B) Your #3 section does indeed support zero rest mass; otherwise, particles with non-zero rest mass cannot travel at the speed of light, as it would require infinite energy. Since photons always travel at the speed of light in vacuum, they must have zero rest mass.
...To be continued? (gotta go now) --136.54.106.120 (talk) 00:03, 2 July 2024 (UTC)
It is (I think) conceivable that not all photons travel at exactly the same speed; if the slowest photons move at a fraction of 10−80 slower than the fastest ones, we would not be able to detect that experimentally. Photons traveling in vacuum are traveling through quantum foam. It is presently unclear if that affects their speed; see Quantum foam § Experimental results --Lambiam 10:51, 2 July 2024 (UTC)
A) See p. 81 in your first source: In section 2, we introduce the theoretical foundation for massive photons, via a discussion of the Proca equations... Using the Proca equations as a starting point, several possible observable effects associated with a nonzero rest mass of the photon are developed in section 3.
B) You are actually repeating what I'd claimed in section 3. However, my question, was not about section 3 you're repeating, nor about my section 2 whose consequence actually contradicts the opposite consequence of my section 3, but rather about whether this contradiction could be removed. For it to be removed, one should show what's wrong in my argument in section 2 or in section 3. For showing what's wrong in such an argument, one should quote the wrong step in that argument and then explain why this step is logically wrong. HOTmag (talk) 11:37, 2 July 2024 (UTC)
"Rest mass" is just another term for "invariant mass", a property of a physical object that is not dependent on the coordinate system of an observer – in contrast to its relativistic mass, which can be different for different observers. When no confusion is possible, physicists will use just "mass" instead of "invariant mass" and describe the photon as a massless particle. This has the same meaning as saying that photons have zero invariant mass, or equivalently that they have zero rest mass. It is pointless to seek more behind this expression. --Lambiam 18:46, 2 July 2024 (UTC)
Re. your first sentence: Yes, this is a well known fact.
Re. your second sentence. Those who use the term "massless" don't recognize the relativistic mass. But if you're among those who do, then you should avoid the confusing term "massless", because any particle (e.g. a photon) carrying no rest mass does carry a non-zero relativistic mass.
Re. your last two sentences: I guess you want to claim that the term "a photon's rest mass" doesn't mean "a photon's mass when at rest". But if so, then "a photon's rest mass" must mean "a photon relativistic mass", whereas this kind of mass is non-zero, so how does this interpretation of "rest mass" relate to my question about those authors who claim that a photon carries a zero rest mass? HOTmag (talk) 20:29, 2 July 2024 (UTC)
This thread reminds me of Codd's Null (SQL). A null indicates a lack of a value, which is not the same thing as a zero value. "No rest mass" seems pretty like the null case. Mike Turnbull (talk) 10:50, 3 July 2024 (UTC)
Yes, Just as the function at is a null case.
So, combining the formulas , and does not let us conclude that a photon carries a zero rest mass because the first formula only refers to bodies carrying a rest mass while a photon's rest mass is a null case - because a photon can't be at rest. HOTmag (talk) 19:07, 3 July 2024 (UTC)
Maybe you overlooked the statement that "rest mass" is just another term for "invariant mass". So "a photon's rest mass" means "a photon's invariant mass". Maybe you also overlooked the mentioned restriction to cases when no confusion is possible. But I fear that for some people confusion is always a possibility. --Lambiam 18:28, 3 July 2024 (UTC)
I didn't overlook the statement that "rest mass" is just another term for "invariant mass". On the contrary, I explicitly pointed out in my last response: Re. your first sentence: Yes, this is a well known fact. So, I already agreed that "rest mass" was just another term for "invariant mass".
I also didn't overlook the mentioned restriction to cases when no confusion was possible. On the contrary, I explicitly pointed out in my last response: Those who use the term "massless" don't recognize the relativistic mass. But if you're among those who do, then you should avoid the confusing term "massless", because any particle (e.g. a photon) carrying no rest mass does carry a non-zero relativistic mass. In other words, those "cases when no confusion is possible" are only those cases when the relativistic mass is not recognized.
To sum up: there are only two kinds of a given body's mass:
A. The body's current relativistic mass. Please notice, the value of this kind of mass is always non-zero, even if the body is a photon.
B. The body's invariant mass, i.e. the body's rest mass, i.e. the relativistic mass the body would have carried if it had been at rest. Please notice, the very existence of this kind of mass depends on whether the body is a massive one or is a photon: If it's a photon, which actually can't have a rest, then it can't have a rest mass either, logically speaking.
My question was about those authors who claimed that a photon carried a zero rest mass, as opposed to B. HOTmag (talk) 18:56, 3 July 2024 (UTC)
From the formula relating relativistic mass to invariant mass, it follows that the invariant mass of a photon must be zero, but its relativistic mass need not be. The phrase "The rest mass of a photon is zero" might sound nonsensical because the photon can never be at rest; but this is just a side effect of the terminology, since by making this statement, we can bring photons into the same mathematical formalism as the everyday particles that do have rest mass.[6] --Lambiam 07:03, 6 July 2024 (UTC)
What are the defining characteristics of the bird clade “telluraves” + what distinguishes birds in its subclade “australaves” from the other subclade, “afroaves”?[edit]
Quickly saying, I asked here because the references are far too complex to understand, and the Wikipedia pages don’t list defining characteristics. 38.23.177.112 (talk) 03:09, 1 July 2024 (UTC)
One reason with I hate phylogeny… without distinguishing traits, how can clades be properly defined?
Am I the only person who hates phylogeny for this particular reason? 38.23.177.112 (talk) 10:22, 1 July 2024 (UTC)
I'm sure it bugs many people. But one can only hate phylogeny if one cares about phylogeny. And unless one is publishing scientific articles in the field, hating it will accomplish nothing. Abductive (reasoning) 21:04, 1 July 2024 (UTC)
I suspect that hating phylogeny will accomplish very little also for people publishing scientific articles in the field. --Lambiam 18:06, 2 July 2024 (UTC)
Does any company still make black and white TVs?[edit]
Just wondering. I had a black and white TV in my room as a kid in the late 80s, used a black and white TV that came with my flat in the early 2000s and (apparently) the TV license in the UK is still cheaper for black and white even now. Iloveparrots (talk) 01:56, 2 July 2024 (UTC)
It seems highly unlikely. Why would anybody continue to make a product for which there is no demand? And if, for some reason, you wanted to view the screen that way, you could just turn the color off on a regular, color TV. Clarityfiend (talk) 08:31, 2 July 2024 (UTC)
Steady on there with the 'no demand'. According to this, there were "4,200 black and white TV licences in force in March 2022" in the UK, and I imagine some of those people are quite demanding. I was thinking about this recently, that families often didn't own TVs back in the black and white days in the UK, they rented them from DER. Maybe not owning things, appliances etc., will make a comeback one day if the price (no cost) and logistics (arrives instantaneously) work. Still waiting for that communist utopia I was promised as a child... Sean.hoyland (talk) 09:55, 2 July 2024 (UTC)
This 2008 BBC article says that new blank & white televisions can still be found in the UK, but I imagine that they would have been from old stock rather than newly manufactured. A reasonably thorough Google search failed to find any actual new ones. Alansplodge (talk) 15:26, 2 July 2024 (UTC)
Blind people qualify for a 50% discount on their UK TV licence; a B&W licence is a third of the price of a colour one. So by going B&W (which they may not be able to see anyway) they pay about one sixth (£28.50) of the full price (£169.50). -- Verbarson talkedits 17:32, 2 July 2024 (UTC)
It seems amazingly regressive that everyone has to pay hundreds of dollars or £169.99 a year to own a TV (more than throwing a basic TV in the Thames every year and almost as much as basic cable just for BBC). In the states they offered everyone a subsidy just to avoid the much cheaper one-time cost of the box to run analog TVs on digital signals. Sagittarian Milky Way (talk) 23:21, 3 July 2024 (UTC)
In the words of Frank Zappa, "Communism doesn't work, because people like to own stuff." Regarding old TV's in stock, I recall not too many decades ago reading that there were still after-market parts available for the Model A Ford, which hadn't been manufactured since the 1930s. ←Baseball BugsWhat's up, Doc?carrots→ 15:38, 2 July 2024 (UTC)
Baseball Bugs, this company says they have over 500,000 Model A parts in stock, and they have quite a few competitors. Cullen328 (talk) 20:11, 5 July 2024 (UTC)
All the better! And I would suspect there are still companies making tubes for old radios and televisions. Not to mention phonograph needles for antique Victrolas. ←Baseball BugsWhat's up, Doc?carrots→ 00:31, 6 July 2024 (UTC)
I saw a YouTube video a while back where someone took a Model T to a Ford service centre. The people there had no problem with fixing it up, for what it's worth. Iloveparrots (talk) 02:27, 6 July 2024 (UTC)
I expanded the concept slightly, and found a bunch of suppliers of new monochrome monitors built with modern technology and wiring (LCD with DVI, etc.). Get a tuner for your favorite local broadcast mode and you're all set. Lots of medical and other imaging is intrinsically monochrome, so there's a market for monitors optimized for high resolution and other visual qualities rather than colors and their rendering properties. DMacks (talk) 16:19, 2 July 2024 (UTC)
Many years ago I had what might be described as "television on the go". It was black and white and the screen was about two inches wide. 2A02:C7B:204:8E00:E0E4:8C0D:4571:6A6F (talk) 14:59, 5 July 2024 (UTC)
Why didn't those very small TVs get more popular than they did? Small battery-powered radios got popular, Walkmen got popular, wireless boomboxes got popular, portable record players got popular. Did they ever reach battery-powered flatscreen color before streaming video crippled sales? Sagittarian Milky Way (talk) 18:55, 5 July 2024 (UTC)
One reason is that they soaked up battery power, and if mains was available why have a tiny TV? Martin of Sheffield (talk) 20:02, 5 July 2024 (UTC)
Watching any sport involving fast activity (e.g. cricket or baseball) would be pointless on such a small screen. Golf would also be challenging. HiLo48 (talk) 01:29, 6 July 2024 (UTC)
I had a couple of pocket TVs back in the day. The reception on them was pretty poor. Like watching everything through snow. Maybe that was the reason? Yes, they also are batteries very fast too. Faster than the original Gameboy, which was notorious for consuming batteries. Iloveparrots (talk) 02:24, 6 July 2024 (UTC)
I'm in suburban northern California and we've had a serious heat wave this week, like 100+F all day reaching 107F in the late afternoon. I've had to go outside a few times and it's tolerable (like a sauna) if I don't stay out too long or do anything strenous. I don't think I could stand being outside all day even under tree cover. I have a contingency plan to head for the ocean (where it is cooler) if the power and AC should happen to go out here.
There are deer and other wildlife in the area. Any idea how they cope? Will they be ok? I think this amount of heat is unusual. Last year it may have hit 103 on a few occasions but not for multi-day periods like this.
There are some natural water sources (creeks) nearby that weren't dried up as of a few weeks ago, but I don't know about now. They did dry up in the worse parts of the drought a few years ago. So that's not so great either. 2601:644:8501:AAF0:0:0:0:9BB0 (talk) 01:11, 6 July 2024 (UTC)
If they are anything like kangaroos they sleep in the forest or other shade during the day and graze at night. During the day you'll see all the sheep and alpacas crammed into whatever shade is available. We don't get deer locally so it may be they can't cope with our heatwaves, but I suspect prevalence of foxes and big feral cats has more to do with that. Greglocock (talk) 03:56, 6 July 2024 (UTC)
