The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Put two equally sized drops, one of each liquid, on a warm surface, wait for them to evaporate, and compare how much salt residue each leaves? Not very precise or measurable, but significant differences should be noticeable. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 10:21, 30 December 2024 (UTC)[reply]
The principle is sound, but the residue from one drop won't be measurable using kitchen equipment -- better to put equal amounts of each liquid in two warm pans (use enough liquid to cover the bottom of each pan with a thin layer), wait for them to evaporate and then weigh the residue! Or, if you're not afraid of doing some algebra, you could also try an indirect method -- bring both liquids to a boil, measure the temperature of both, and then use the formula for boiling point elevation to calculate the saltiness of each! 2601:646:8082:BA0:BD1B:60D8:96CA:C5B0 (talk) 18:22, 30 December 2024 (UTC)[reply]
Presumably the liquid preparations are not simple saline solutions, but contain other solutes - or else one could simply use a hydrometer. It is unlikely that Lambian is afraid of doing some algebra. catslash (talk) 18:57, 30 December 2024 (UTC)[reply]
Assuming the liquid preparations are water-based and don't contain alcohols and/or detergents one can measure their rates of dispersion. Simply add a drop of food dye to each liquid and then time how rapidly droplets of each liquid disperse in distilled water. Materials needed: food dye, eye dropper, distilled water, small clear containers and a timer.Modocc (talk) 21:09, 30 December 2024 (UTC)[reply]
The colligative properties of a solution will indicate its molarity, but not identify the solute. Liquid preparations that might be found in a kitchen are likely to contain both salt and sugar. Electrical conductivity is a property that will be greatly affected by the salt but not the sugar (this does not help in distinguishing Na+ from K+ ions though). catslash (talk) 22:23, 30 December 2024 (UTC)[reply]
Quantitative urine test-strips for sodium seem to be available. They're probably covering the concentration range of tens to hundreds millimolar. DMacks (talk) 00:58, 2 January 2025 (UTC)[reply]
Thanks, test strips seem more practical in the kitchen setting than an ohmmeter (why not call it a "mhometer"?), for which I'd need to devise a way (or so I think) to keep the terminals apart at a steady distance. Test strips require a colour comparison, but I expect that a significant difference in salinity will result in a perceptible colour difference when one strip is placed across the other. Only experiment can tell whether this expectation will come true. Salinity is usually measured in g/L; for kitchen preparations a ballpark figure is 1 g/L. If I'm not mistaken this corresponds to (1 g/L) / (58.443 g/mol) ≈0.017 M = 17 mM. I also see offers for salinity test strips, 0–1000 ppm, for "Science Education". --Lambiam11:40, 2 January 2025 (UTC)[reply]
Test strips surely come with a printed color-chart. But if all you are trying to do is determine which is more salty, then that's even easier than quantifying each separately. Caveat for what you might find for sale: some "salinity" tests are based on the chloride not the sodium, so a complex matrix that has components other than NaCl could fool it. DMacks (talk) 18:44, 2 January 2025 (UTC)[reply]
The (uncommon?) terms "relativistic length", and "relativistic time".
1. In Wikipedia, the page relativistic length contraction is automatically redirected to our article length contraction, which actually doesn't mention the term "relativistic length" at all. I wonder if there is an accepted term for the concept of relativistic length.
2. A similar qusestion arises, at to the concept of relativistic time: The page relativistic time dilation, is automatically redirected to our article time dilation, which prefers the abbreviated term "time dilation" (59 times) to the term "relativistic time dilation" (8 times only), and nowhere mentions the term "relativistic time" alone (i.e. without the third word "dilation") - although it does mention the term "proper time" for the shortest time. Further, this article doesn't even mention the term "dilated time" either. It does mention, though, another term: coordinate time, but regardless of time dilation in Special relativity. To sum up, I wonder what's the accepted term used for the dilated time (mainly is Special relativity): Is it "coordinate time"? "Relativistic time"?
Are you reading these things as "contraction of relativistic length" etc.? It is "relativistic contraction of length" and "relativistic dilation of time". --Wrongfilter (talk) 09:37, 30 December 2024 (UTC)[reply]
When I wrote: The page relativistic time dilation is automatically redirected to our article time dilation which...nowhere mentions the term "relativistic time" alone (i.e. without the third word "dilation"), I had already guessed that the term "dilation of relativistic time" (i.e, with the word "dilation" preceding the words "relativistic time") existed nowhere (at least in Wikipedia), and that this redirected page actually meant "relativistic dilation of time". The same is true for the redirected page "relativistic length contraction": I had already gussed it didn't mean "contraction of relativistic length", because (as I had already written): the article length contraction...doesn't mention the term "relativistic length" at all.
Thank you. The middle source uses the term "comparative length", rather than "relative length". I couldn't open the third source. HOTmag (talk) 08:04, 1 January 2025 (UTC)[reply]
The text under the graph labelled Comparative length on page 20 of the middle source reads:
Graph of the relative length of a stationary rod on earth, as observed from the reference frame of a traveling rod of 100cm proper length.
Is there any metric unit whose ratio is not power of 10, and is divisible by 3? Is there any common use for things like "2⁄3 km", "5⁄12 kg", "3+1⁄6 m"?
Is a one-tenth of nautical mile (185.2 m) used in English-speaking countries? Is there a name for it?
Has anyone determined whether it is better for a right-hander to have the left hand on the steering wheel and the right hand on the gear shift stick, or the other way round? Are there other tests of whether left-hand drive or right-hand drive is physiologically better (for a right-hander at least)? 178.51.7.23 (talk) 12:03, 1 January 2025 (UTC)[reply]
Supplementary question: I've only driven right-hand-drive vehicles (being in the UK) where the light stalk is on the left of the steering column and the wiper & washer controls are (usually) on the right. On a l-h-drive vehicle, is this usually the same, or reversed? {The poster formerly known as 87.81.230.195} 94.6.84.253 (talk) 12:12, 2 January 2025 (UTC)[reply]
Modern cars are designed for mass production in RH- and LH-drive versions with a minimum difference of parts. Steering columns with attached controls are therefore unchanged between versions. Philvoids (talk) 12:29, 2 January 2025 (UTC)[reply]
In the UK, sales of new automatics have just recently overtaken manuals - so probably still more manuals than automatics on the road. catslash (talk) 14:37, 2 January 2025 (UTC)[reply]
In Australia, we drive on the left, and the indicator and wiper stalks are the opposite way to the UK. Having moved back from the UK after 30 years, it took me a while to stop indicating with wipers. TrogWoolley (talk) 05:08, 3 January 2025 (UTC)[reply]
This depends more on where the car came from I think. For European or American cars it tends to be in the UK direction. For Asian cars or I guess those odd Australian made cars which are out there, it tends to be in the other. See e.g. [4]. The UK being a bigger market I think most manufacturers have come to follow the new UK norm for cars they intend to sell there [5][6][7][8] although I suspect to some extent it's still true in the sense that I think most Asian car brands, at least assemble their cars in the EU or maybe the UK if they're destined for the UK (made a lot of sense pre-Brexit) [9]. It sounds like the new UK norm is fairly recent perhaps arising in the 1980s-1990s after European manufacturers stopped bothering changing that part of the production for the reasons mentioned by Philvoids. As mentioned in one of the Reddit threads, the UK direction does make it difficult to adjust indicators while changing gear which seems a disadvantage which is fairly ironic considering the the UK has much more of a preference for manuals than many other RHD places with the other direction. Nil Einne (talk) 04:31, 6 January 2025 (UTC)[reply]
For further clarity, AFAICT, LHD vehicles generally have their indicators on the left and wipers on the right. As mentioned, assuming the gear stick is in the middle which AFAIK it is for most cars by now, this seems the better positioning especially on manual cars since you're much more likely to want to need to indicate while changing gear than you are going to want to adjust your wipers even in the rainy UK. The UK being LHT/RHD especially with their own manufactured cars tended to have the indicators on the right and wipers on the left in the more distant past so again the positions that made most sense.
While I don't have a source for this going by the history and comments, it sounds to me like what happened is European manufacturers who were primarily making LHD vehicles, with the UK and Ireland their main RHD markets but still small compared to the LHD market stopped bothering changing positions for RHD vehicles as a cost saving measure. So they began to put wipers on the right and indicators on the left even in their RHD vehicles no matter the disadvantage. I'm not so sure what the American manufacturers did or when and likewise the British but I think they were a fairly small part of the market by then and potentially even for them LHD was still a big part of their target market.
Meanwhile Asian manufacturers however still put their indicators on the right and wipers on the left in RHD vehicles, noting that Japan itself is LHT/RHD. I suspect Japanese manufacturers suspected, correctly, that it well worth the cost of making something else once they began to enter the LHD markets like the US, to help gain acceptance. And so they put the indicators on the left and wipers on the right for LHD vehicles even if they did the opposite in their own home market and continued forever more. Noting that the predominance of RHT/LHD means even for Japanese manufacturers it's generally likely to be their main target by now anyway.
Later I assume South Korea manufacturers and even later Chinese felt it worth any added cost to increase acceptance of their vehicles in LHT/RHD markets in Asia and Australia+NZ competing against Japanese vehicles which were like this. And this has largely continued even if it means they need to make two different versions of the steering column or whatever. It sounds like the European and American brands didn't bother but they were primarily luxury vehicles in such markets so it didn't matter so much.
This lead to an interesting case for the UK. For the Asian manufacturer, probably many of them were still making stuff which would allow them to keep putting the indicators on the right and wipers on the left for RHD vehicles as they were doing for other RHD markets mostly Asian. And even if they were assembling them in the EU, I suspect the added cost of needing to ship and keep the different components etc and any difference it made to the assembly line wasn't a big deal.
So some of did what they were doing for the Asian markets for vehicles destined for UK. If they weren't assembling in the EU, it made even more sense since this was likely what their existing RHD assembly line was doing. But overtime the UK basically adopted the opposite direction as the norm no matter the disadvantages to the extent consumers and vehicle enthusiast magazines etc were complaining about the "wrong" positions. So even Asian manufacturers ended up changing to the opposite for vehicles destined to the UK to keep them happy. So the arguably better position was abandoned even in cases where it wasn't much of a cost saving measure or might have been even adding costs.
One thing I didn't consider when writing above is how often the steering column or whatever for Asian manufacturers is actually produced in the EU rather than simply shipped there after production elsewhere. That would likely mean producing two would likely incur more additional cost even if the same thing in two versions is produced elsewhere for use in the Asian market. I still think the main reason Asian manufacturers stopped using the opposite location/direction in the UK is primarily one of consumer demand, but it's true that it's fairly complicated. Nil Einne (talk) 10:28, 10 January 2025 (UTC)[reply]
I've driven different (automatic) left-hand-drive vehicles with the light stalk on each side, but left side has been more common. Perhaps because the right hand is more likely to be busy with the gear shift? (Even in the US, where automatic has been heavily dominant since before I learned to drive.) -- Avocado (talk) 17:32, 2 January 2025 (UTC)[reply]
It's better for a right-hander to have both hands on the steering wheel regardless of where the gear lever is. See Rule 160. I suspect the same goes for a left-hander. Bazza 7 (talk) 14:39, 2 January 2025 (UTC)[reply]
I suppose that the question is whether right-handers have an easier time operating the gear stick when changing gears in manual-transmission cars designed for left-hand traffic, with the steering wheel on the right (like in the UK) or right-hand traffic, with the steering wheel on the left (like in most of continental Europe). Obviously, drivers will use their hand at the side where the gear stick is, so if it is in the middle and the driver, behind the wheel, sits in the right front seat, they'll use their left hand, regardless of their handedness. But this may be more awkward for a rightie. Or not.
In my personal experience (more than 10 years driving on each side of the road, in all four combinations of car handedness and road handedness) the question which hand to use for shifting gears is fairly insignificant. Switching from one type of car to the other is a bit awkward though. —Kusma (talk) 18:33, 2 January 2025 (UTC)[reply]
Is there a way (if you don't know which way is west and which way is east in a particular location) to distinguish a picture of a sunset from the picture of a sunrise? 178.51.7.23 (talk) 12:08, 1 January 2025 (UTC)[reply]
Generally, no, but there are a few tricks that sometimes work. In dry sunny weather, there's more dust in the air at sunset (due to thermals) than at sunrise, making the sky around the sun redder at sunset. But in moist weather, mist has the same effect at sunrise. If the picture is good enough to see sunspots, comparing the distribution of sunspots to the known distribution of that day (this is routinely monitored) tells you where the North Pole of the sun is. At sunset, the North Pole points somewhat to the right; at sunrise, to the left. If you see any cumulus or cumulonimbus clouds in the picture, it was a sunset, as such clouds form during the day and disappear around sunset, but absence of such clouds doesn't mean the picture was taken at sunrise. A very large cumulonimbus may survive the night. Cirrus aviaticus clouds are often very large, expanding into cirrostratus, in the evening, but are much smaller at dawn as there's more air traffic during the day than at night, making the upper troposphere more moist towards the end of the day. Cirrostratus also contributes to red sunsets and (to lesser extend, as there's only natural cirrostratus) red sunrises. Dew, rime, flowers and flocks of birds may also give an indication. And of course human activity: the beach is busier at sunset than at sunrise. PiusImpavidus (talk) 13:41, 1 January 2025 (UTC)[reply]
Supposing the photograph has high enough resolution to show Sunspots it can be helpful to know that the pattern of spots at sunrise is reversed left-right at sunset. Philvoids (talk) 13:21, 3 January 2025 (UTC)[reply]
At the equinox, the disk of the Sun with its pattern of sunspots appears to rotate clockwise from sunrise to sunset by 180 degrees minus twice your latitude (taking north positive). At my place, that's 75 degrees. Other times of the year it's less; at the start and end of polar day and polar night, there's no rotation. Sunset and sunrise merge then.
And I forgot to mention: cirrostratus clouds will turn red just after sunset or just before sunrise. At the exact moment of sunrise or sunset, they appear pretty white. PiusImpavidus (talk) 17:06, 3 January 2025 (UTC)[reply]
I differ: the same rotation is involved everywhere on Earth. If you stand on tiptoe at a N. or S. pole to take a picture of the Sun it is you who must pirouette 15 degrees per hour to keep facing the Sun. The Earth rotates you at this rate at all non-polar locations. If you stand within the arctic or antarctic circles, for parts of the year the 24-hour night or 24-hour daylight seem to prevent photographs of sunrise or sunset. However the terms "sunrise" and "sunset" can then be interpreted as times that are related to particular timezones which are generally assigned by longitude. In photographing the 24-hour Sun the equatorial rise and set times for your own longitude are significant elevation maxima worth mentioning even though the minimum elevation remains above the horizon. I maintain that the sunspot pattern observed from any location on Earth rotates 360 degrees per 24 hours and that "night", the darkness from sunset to sunrise, is when the Earth's bulk interrupts one's view of the rotation but not the rotation itself which is continuous.
Taking the Earth as reference frame, the Sun rotates around the Earth's spin axis. The observer rotates around his own vertical axis. The better both axes are aligned, the smaller the wobble of the Sun. In the northern hemisphere, it rotates clockwise from about 6 till 18 by 180 degrees minus twice your latitude and counterclockwise at night, in the southern hemisphere it's the opposite. Try a planetarium program if you want to see it. Stellarium shows some sunspots, does things right and is free and open source. PiusImpavidus (talk) 10:27, 5 January 2025 (UTC)[reply]
Relationship between Earth's axial tilt (ε) to the tropical and polar circlesWe deprecate the obselete Geocentric model and suggest Wikipedia references that are free and just one click away (no extra planetarium software needed). The axes of rotation of the Sun and Earth have never in millions of years aligned: the Ecliptic is the orbital plane of Earth around the Sun and Earth currently has an Axial tilt of about 23.44° without "wobbling" enough from this to concern us here. Philvoids (talk) 14:56, 5 January 2025 (UTC)[reply]
This isn't my field but sunspots aside, if you know the location and date, I assume the appearance of other astronomical objects like the moon or rarely another star probably Venus, in the photograph should be enough to work out if it's a sunset or sunrise. That said, to some extent by taking into account other details gathered from elsewhere's I wonder if we're going beyond the question. I mean even if you don't personally know which is east or west at the time, if you can see other stuff and you know the location or the stuff you can see is distinctive enough it can be worked out, you can also work out if it's sunset or sunrise just by working out if it's east or west that way. Nil Einne (talk) 03:54, 6 January 2025 (UTC)[reply]
In my experience (Southern England) they tend to be pinker at dawn and oranger(!) at dusk. {The poster formerly known as 87.81.230.195} 94.6.84.253 (talk) 03:23, 4 January 2025 (UTC)[reply]
Pink clouds must result from blending of reddish clouds with the blue sky behind. There's actually more air between the observer and the clouds than behind the clouds, but for that nearby air the sun is below the horizon. PiusImpavidus (talk) 10:27, 5 January 2025 (UTC)[reply]
The questioner asks for interpretation of a single picture. It is beside the point that more would be revealed by a picture sequence such as of changing cloud colours. Philvoids (talk) 12:41, 4 January 2025 (UTC)[reply]
Which you can only tell if you know which way is east in the image. Maltin, or his writer, appears to have assumed that Vietnam has a seacoast only on the east, which is wrong. --142.112.149.206 (talk) 03:46, 6 January 2025 (UTC)[reply]
But as it was filmed in (The US State of) Georgia, it must actually show a sunrise, regardless of what the story line says – how do you know that wasn't what Maltin actually meant? {The poster formerly known as 87.81.230.195} 94.6.84.253 (talk) 10:35, 7 January 2025 (UTC)[reply]
Because things filmed for movies often are not actually what they are shown as being, so that wouldn't be interesting and Maltin's guide wouldn't waste space on it. If what they show it as — for example, in Krakatoa, East of Java — is wrong or impossible, that could be interesting. --142.112.149.206 (talk) 17:43, 8 January 2025 (UTC)[reply]
I assume (not having seen the film) that, in the story line of The Green Berets , the closing scene takes place in the late afternoon, which means it shows a sunset. The plot section of our article on the film places the closing scene at or near Da Nang, which is on the east coast of Vietnam. This means that Maltin did not make an unwarranted assumption; he was just seeking an excuse to bash the film. --Lambiam13:55, 7 January 2025 (UTC)[reply]
It would be unusual to express the situation in such terms. Since the notion of energy "belonging to" some entity is not itself a physical concept – any practical approach to energy bookkeeping that satisfies the law of conservation of energy will do – this cannot be said to be wrong. It is, however, (IMO) not helpful. Does an apple belong to the space it occupies? Or does that space belong to the apple? --Lambiam23:37, 6 January 2025 (UTC)[reply]
First, I let you replace the notion of energy "belonging to" some entity, by the notion of energy "attributed to" some entity, or by the notion of energy "carried by" some entity, and the like. In other words, I'm only asking about the abstract relation (no matter what words we use to express it), between the energy and the space carrying the electromagnetic field, rather than about the specific term "belong to".
Second, I'm only asking about what the common usage is, rather than about whether such a usage is wrong or helpful.
The question is actually as follows: Since it's accepted to attribute energy to an electromagnetic field, is it also accepted to attribute energy to the space carrying that field?
The answer remains the same. It would be a highly unusual use of language to "attribute" electromagnetic energy to a volume of space, in quite the same way as it would be strange to "attribute" the mass of an apple to the space the apple occupies. But as long as an author can define what they mean by this (and that meaning is consistent with the laws of physics), it is not wrong. --Lambiam13:21, 7 January 2025 (UTC)[reply]
An electromagnetic field that we may (even tenuously) conceive to have the form of a massless photon has, like the aforementioned apple (a biological mass) its own unique history, that being a finite path in Spacetime. I reject apparent effort to give spacetime any kind of identity capable of owning, or even anticipating owning or remembering having owned anything at all. Concepts of owning12, attributing3 or whatever synonymous wordplay one chooses all assume identification that can never be attached to the spacial location of an em field. The energy of the photon is fully accounted for, usually as heat at its destination, when it is absorbed and no lasting trace remains anywhere. I am less patient than Lambian in my reaction to this OP who under guise of interest in surveying "what is commonly accepted" returns in pursuit of debate by patronisingly "allowing" us to reword his question in abstract "words that don't matter" to make it purportedly clearer and worth responders' time. Philvoids (talk) 14:55, 7 January 2025 (UTC)[reply]
Nonsense. I have it on good authority—Fosters own ads on TV in the US two decades ago—that all Australians do nothing but drink Fosters all day because it is the one true Australian beer. DO NOT ARGUE WITH YOUR CAPITALIST OVERLORDS' CULTURAL APPROPRIATION! Um, I mean, Foster's Lager had a bunch of ad campaigns promoting their image as being Australian. See its article for details. Search youtube for fosters australian to see some examples. DMacks (talk) 01:28, 9 January 2025 (UTC)[reply]
It's all grade-separated (rail-line vs rail-line). I assume they mean one rail-line is on the ground (in contrast with being on a bridge as the first example). The term is annoying, but we're stuck with terms like at-grade railway. DMacks (talk) 05:38, 9 January 2025 (UTC)[reply]
There is one on the Driving Creek Railway (no photo of this detail in the article, but a few in c:Category:Driving Creek Railway). I've seen mentions of some others that are long-gone (or have one or both levels now used for other modes). Lots of pictures of old New York City have an el with rails in the street under it, but nothing still existing or in-use. DMacks (talk) 07:25, 9 January 2025 (UTC)[reply]
Exactly the same as a map would indicate a railway under a roadway or a roadway under a railway (or anything under anything), of which there are numerous examples on maps, i.e. the lower railway disappears under the upper railway and then reappears at the other end of the bridge. Shantavira|feed me10:27, 10 January 2025 (UTC)[reply]
Thanks! Which would actually make it easier if the two railroads are of different gauges and one of them is at grade, as in my (fictional) example (I'm currently mapping the station layouts on the North Western Railway for a possible scenario pack for Train Sim Classic and/or Train Sim World, and there's a setup just like I describe at Arlesburgh West -- the narrow-gauge Arlesdale Railway goes up on a coal trestle above an at-grade siding of the North Western) -- in that case, the standard-gauge line goes under the ends of the bridge lengthwise and disappears, while the narrow-gauge line remains continuous on the bridge deck, and because they have different symbols there's no confusion! 2601:646:8082:BA0:48AA:9AA4:373D:A091 (talk) 22:11, 10 January 2025 (UTC)[reply]
Why does pork belly always seem to pop in a microwave whenever I cook it in there? It also splatters, too, which creates a mess I have to clean up. Kurnahusa (talk) 02:53, 11 January 2025 (UTC)[reply]
Pork belly contains a layer of fat. Fat tends to heat up very fast in the microwave. This brings watery fluids in contact with the hot fat quickly to a boil, well before the boiling temperature would have been reached in lean meats. The splattering happens when internal steam bubbles under high pressure force their way out and pop. --Lambiam09:17, 12 January 2025 (UTC)[reply]
Bird from Brenman Park, Alexandria, Virginia, February last year.
I found this picture on Commons. Is this really a mallard (Anas platyrhynchos)? We have lots of mallards here in Sweden where I live, and nor male or female looks like that.
I'm sure it belong to Anseriformes, yes... but what kind of bird species?
Info from Flickr images says this is purple-faced langur...
I found this picture on Commons. Description says Purple-faced langur, and so did the category. I changed the category to Semnopithecus vetulus, but I'm not sure the picture shows Purple-faced langur/Semnopithecus vetulus.
Going by the long nose and concave facial profile, that looks to me like a macaque. In fact, based on the ludicrous hairstyle, the first second last on the list, Toque macaque, is indicated. It is endemic to Sri Lanka like the Purple-faced langur. These individuals in the picture do have very purple faces, I must admit. Perhaps it was mating season and they go like that? But monkeys tend to send that kind of signal via the butt, not the face. Our article says "With age, the face of females turns slightly pink. This is especially prominent in the subspecies M. s. sinica", so I suppose that could be it.
In "Newton's law of motion", chapter Singularities we find this text: "It is mathematically possible for a collection of point masses, moving in accord with Newton's laws, to launch some of themselves away so forcefully that they fly off to infinity in a finite time."
How can one write such a thing, when by definition infinity has no limit and whatever the speed of a point mass, it will therefore never reach infinity, that is to say a limit that does not exist? Malypaet (talk) 22:07, 11 January 2025 (UTC)[reply]
Looking at the citation, we find an article entitled "Off to infinity in finite time".[10] I didn't find it at all answers your question, though. What does it mean? --jpgordon𝄢𝄆𝄐𝄇02:48, 12 January 2025 (UTC)[reply]
I would assume it means there's some finite time in the future such that, for any natural number , there's a time such that the object is more than meters away at every time between and .
If the point mass flies off to infinity in finite time, its velocity must be infinite. But simply having infinite velocity in itself isn't a real problem, if the velocity is held for an infinitesimal period of time. Therefore the statement is made in terms of distance.
Newtons laws occasionally give some infinities if you put in zeros at the wrong place. What it really tells us is that there're no point masses in real life – as far as Newton is concerned. PiusImpavidus (talk) 11:21, 12 January 2025 (UTC)[reply]
No, the velocity does not have to be infinite. You can have finite velocity at every moment before the time at which the distance approaches infinity. You just need the integral of the velocity to diverge to infinity. --Trovatore (talk) 18:26, 12 January 2025 (UTC)[reply]
The question should be raised at Talk:Newton's laws of motion instead of on this desk where the OP extracts an incomplete statement about Newton's laws of motion#Singularities. Important provisos lack and we are left in doubt about what is happening that may involve launching by unspecified agency, and whether "fly off to infinity in a finite time" means (i)"start in a finite time on an infinite outward path" or (ii)"travel to infinity in a finite time". The OP sees meaning (ii) and queries it as untenable. The alternative (i) can be taken to mean achieving Escape velocity.
I propose the following rewording to clarify the article text.
Singularities
Mathematicians have investigated the behaviour of collections of point masses that may approach one another arbitrarily closely, possibly collide together, and move in accord with Newton's laws. In simulations that impose no relatavistic speed limit, singularities of unphysical behavior are observed. For example, a particle velocity can accumulate through successive near-collisions to the extent of theoretically departing the system to infinity in a finite time.[54] [61] [62] are existing references that can be located in the paragraph.Philvoids (talk) 15:23, 12 January 2025 (UTC)[reply]
None of the references talk about simulations (certainly not the article linked to above [54], and apparently none of the others). Singularities, and things flying off to infinity, are not (easily) simulatable. Your interpretation (i) also doesn't seem very plausible. Interpretation (ii) simply means that the integral converges and yields a finite value. The (rather weak) mathematical condition is that the velocity increases with distance faster than linear. The question now is whether such a velocity can be achieved given the Newtonian ingredients, in addition to point particles and the lack of a speed limit that involves the gravitational field, which of course vanishes at infinity, but diverges for . To the extent that I understand the article, the authors set up a situation where a particle bounces between two very carefully set-up and timed binaries (near-colliding) which causes the particle to bounce fast enough for it to cover an infinite distance in a finite time. This some way to answering the question but not all the way because the motion of the particle is still bounded between the two binaries and does not go off to infinity. Unfortunately, the article then loses me by going into Cantor sets and whathaveya, and I'm not sure whether they manage to generalise to the actual situation that they promise in the title. In any case, the exercise is a mathematical curiosity and clearly not physically realisable. --Wrongfilter (talk) 16:36, 12 January 2025 (UTC)[reply]
"cover an infinite distance in a finite time": covering an infinite distance never ends by definition, whatever the velocity, so there can be no finite time. If we consider the problem posed textually, this is as true in mathematics as in physics. In addition, I am not sure that the integral posed here is the right one, because the distance interval whose sum goes from 0 to infinity is a variable if the velocity is increasing non-linearly for a constant time interval ds. Malypaet (talk) 22:36, 12 January 2025 (UTC)[reply]
Something that seems hard to find online is how many % of Earth's land area's older than each Phanerozoic period+Cenozoic epoch on those maps of which period/epoch is the top layer. Google AI dumbass says 88% Precambrian which is clearly just how much of the yrs the acres isn't 88% craton shield. Sagittarian Milky Way (talk) 03:58, 13 January 2025 (UTC)[reply]
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