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December 19

Does human DNA become weaker with each generation?

As with photocopying something over and over, the text becomes less clear each time.

Does human DNA become weaker with each generation? HarryOrange (talk) 21:22, 19 December 2024 (UTC)

Sure, DNA replication is not perfect, although proofreading reduces the error rate to about 1 mistake per 10 nucleotides (see our article on DNA Replication). But that is per generation of cells, not of the whole organisms. Many mutations will be neutral in effect (because much of our DNA is redundant), some will be deleterious, and a few might be advantageous. It is the process of natural selection that hinders the spread of deleterious mutations: sometimes this aspect is called purifying selection. One thus usually expects a stable mutation–selection balance over time rather than that "DNA becomes weaker with each generation". Medical science is reducing the selection pressure against some mutations, which consequently may become more common. One of the problems for asexual organisms is referred to as Muller's ratchet; assuming that reverse mutations are rare, each generation has at least the mutational load of its predecessor. In contrast, in sexual organisms genetic recombination generates the variation that, combined with selection, can repair the situation. Sexual organisms consequently have a lighter genetic load. JMCHutchinson (talk) 22:42, 19 December 2024 (UTC)

So purifying selection won't work properly in case of Inbreeding ? HarryOrange (talk) 23:16, 19 December 2024 (UTC)

The larger the degree of inbreeding, the larger the chance that deleterious traits are expressed. But this very expression of traits leading to decreased biological fitness of their bearers is what actually enables purifying selection in the longer term.  --Lambiam 23:36, 19 December 2024 (UTC)

@Lambiam so DNA repair won't stop these deleterious traits to get expressed? HarryOrange (talk) 14:11, 20 December 2024 (UTC)

No, this is not an issue of damage to the DNA. The genes involved are faithfully reproduced and passed on from generation to generation.  --Lambiam 15:53, 20 December 2024 (UTC)

Or stronger e.g. "...we found that genes specifically duplicated in the Greenland shark form a functionally connected network enriched for DNA repair function", and those guys live for centuries and have much more DNA than us. Sean.hoyland (talk) 15:21, 20 December 2024 (UTC)

@Lambiam If not due to DNA damage, why do babies from inbreeding appear like DNA-damaged species? HarryOrange (talk) 17:29, 20 December 2024 (UTC)

Inbred offspring of species that normally outcross may show abnormalities because they are more likely than outcrossed offspring to be homozygous for recessive alleles that are deleterious. In individuals that are heterozygous at these loci, the recessive alleles will not be expressed (because the other wild-type dominant allele is sufficient to do their job adequately). See our article on inbreeding depression. JMCHutchinson (talk) 19:26, 20 December 2024 (UTC)

Larvae going south

In a novel I've just finished (The Chemistry of Death by Simon Beckett) he writes:

• leave the body in an orderly fashion, following each other in a neat procession that always heads south. South-east or south-west sometimes, but never north. No-one knows why.

The author has done considerable international research on the science of forensic identification of decayed bodies and I assume his details can be trusted.

I've looked online for any verification of this surprising statement, but found only this, which seems to debunk it.

Is there any truth to this? -- Jack of Oz 23:38, 19 December 2024 (UTC)

Can't speak to its truth, but . . .

• Does Beckett state this in his own auctorial voice (i.e. as an omniscient narrator)? If so, he might be genuinely mistaken.
• The book was published nearly 20 years ago, what was the accepted wisdom then?
• What specific species (if any) is the book describing? – your linked Quora discussion refers only to "maggots" (which can be of numerous species and are a kind of larva, but there are many others, including for example Processionary caterpillars).
• Alternatively, if the statement is made by a character in the book, is that character meant to be infallible, or is he portrayed as less than omniscient, or an 'unreliable narrator'?

Regarding the statement, in the Northern hemisphere the arc of South-east to South-west is predominently where the Sun is found well above the horizon, the North never, so the larvae involved might simply be seeking maximum warmth or light. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 02:18, 20 December 2024 (UTC)

This appears in the very first paragraph of Chapter I, which starts out:

• A human body starts to decompose four minutes after death. Once the encapsulation of life, it now undergoes its final metamorphoses. It begins to digest itself. Cells dissolve from the inside out. Tissue turns to liquid, then to gas. No longer animate, the body becomes an immovable feast for other organisms. Bacteria first, then insects. Flies. Eggs are laid, then hatched. The larvae feed on the nutrient-rich broth, and then migrate. They leave the body in an orderly fashion ... (then the quote above completes the paragraph).

It's not until para 2 that he starts talking about any human characters, and not until para 4 that he invokes the first person.

That's as much as I know. But I find it hard to believe he'd just make up a detail and put it in such a prominent place if it could so easily be debunked if it were not true. -- Jack of Oz 02:39, 20 December 2024 (UTC)

I wonder how they would measure the migratory path of maggots within a sealed coffin. ←Baseball Bugs carrots→ 02:51, 20 December 2024 (UTC)

The context of the novel is about finding decaying corpses that have been dumped in a forest. No coffins involved. -- Jack of Oz 06:08, 20 December 2024 (UTC)

Baseball Bugs, see also body farm research facilities. Alansplodge (talk) 13:44, 20 December 2024 (UTC)

Could it be that the larvae are setting off in search of another corpse? The prevailing wind in the UK is from the south-west, so by heading into the wind they won't be distracted by the frangrance of the one they've just left. Shantavira| 09:30, 20 December 2024 (UTC)

If you can, have a look at 'Heinrich, Bernd. “Coordinated Mass Movements of Blow Fly Larvae (Diptera: Calliphoridae).” Northeastern Naturalist, vol. 20, no. 4, 2013, pp. N23–27. JSTOR, http://www.jstor.org/stable/43288173.' Here are some extracts

• On the fourth day, after a cooling night with dew on the grass, a stream of tens of thousands of larvae exited from beneath the carcass within 1 h after sunrise, and proceeded in a single 1-2-cm-wide column directly toward the rising sun...
• However, in this case, the larvae left at night, within 1 h after a cloudburst (at 21 :00 hours). But, unlike before, this nocturnal larval exodus in the rain was diffuse; thousands of larvae spread out in virtually all directions over an 8 m2area. Apparently, the sudden moisture had cued and facilitated the mass exodus, but the absence of sun had prevented a unidirectional, en masse movement.
• However, on the following morning as the sun was starting to illuminate the carcass on the dewy grass, masses of larvae gathered at the east end of the carcass at 07:00 hours. In one half hour later, they started streaming in a column directly (within one degree) toward the rising sun, and the carcass was then nearly vacated.

It goes on. Maggot migration appears to be a bit more complicated than the novel suggests. Sean.hoyland (talk) 09:39, 20 December 2024 (UTC) I suppose you could try to address it from the other direction and look at the technology your average maggot has access to in terms of light detection, heat detection, olfactory systems, orientation in magnetic fields (like many arthropods) etc. They presumably have quite a lot of tools. Sean.hoyland (talk) 10:13, 20 December 2024 (UTC)

If orderly migrating maggots tend to move towards the sun, they should display a northward tendency in Oztralia.  --Lambiam 10:31, 20 December 2024 (UTC)

Maybe, but the novel is set in England.

I must say, as soon as I read the quoted para for the first time, my immediate thought was that it might have something to do with the magnetic field of the earth. -- Jack of Oz 10:42, 20 December 2024 (UTC)

Prime suspect might be the Bolwig organ, the photoreceptor cluster many fly larvae have. Sean.hoyland (talk) 10:49, 20 December 2024 (UTC)

Obviously, Jack, you need to create a corpse, place it in a nearby forest, and carefully observe which way the maggots go. For Science! And Literary Criticism! {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 21:01, 20 December 2024 (UTC)

December 20

Winter solstice and time of sunrise?

How is it that despite December 21st supposedly being the shortest day of the year, sunrise here happens later and later until December 26 and only on January 05 starts to turn around to occur earlier and earlier. On December 25 it takes place at about 08:44, between December 26 and January 04 it takes place at about 08:45, and on January 05 it takes place again at about 08:44. (Google rounds out the seconds). Is it Google's fault? Is it everywhere the same? Confused in Brussels, Belgium. 178.51.16.158 (talk) 12:06, 20 December 2024 (UTC)

The pertinent article is Analemma, start with the section Earliest and latest sunrise and sunset. The details are not that simple to understand, but it's basically due to the ellipticity of Earth's orbit and its axial tilt. --Wrongfilter (talk) 12:22, 20 December 2024 (UTC)

Also note that sunset begins to be later on 22 December so that the time between sunrise and sunset is a few seconds longer than on 21 December (3 seconds longer on 22/12/24 in Brussels according to this). Alansplodge (talk) 13:33, 20 December 2024 (UTC)

Also see Equation of time#Major components. The obliquity of the ecliptic (that is, the Earth's axial tilt) is the main component and hardest to understand. But the idea is that the time when the Sun is exactly south (that is, the true noon) moves some minutes back and forth throughout the year and it moves quite rapidly to later times in late December. PiusImpavidus (talk) 19:05, 20 December 2024 (UTC)

By the way is there a chart somewhere of the date of earliest/latest sunrise/sunset by latitude? —Tamfang (talk) 21:45, 29 December 2024 (UTC)

Discussed at Misplaced Pages:Reference desk/Archives/Science/2024 August 9#Total daytime per latitude. 2A02:C7C:F33B:4100:909B:C596:FD17:F530 (talk) 13:42, 30 December 2024 (UTC)

Three unit questions

1. Why territorial waters are defined by nautical miles instead of kilometers?
2. Why GDP is usually measured in US dollars rather than euros? Euro would be better because it is not tied into any country.
3. Are there any laws in United States that are defined by metric units?

--40bus (talk) 23:30, 20 December 2024 (UTC)

Question 1

1. There were nautical miles in use before there were kilometers. - Philvoids 00:52, 21 December 2024

Do any people use metric units in marine and air navigation like "The ship is 10 kilometers from the port", "The plane is 10 kilometers from the destination? And is there any European country with metric flight levels? --40bus (talk) 07:22, 21 December 2024 (UTC)

Inland shipping (rivers, canals and lakes) in Europe (except the UK) is fully metric. Ships going for example Tilbury – Duisburg may have to switch units along the way. Gliders and ultralight aircraft in Europe often use metric instruments and airport dimensions are also metric (including runway length). Countries are free to define their territorial waters in whatever way they deem fit, so with nautical miles having no legal status in a fully metric country, they may define their territorial waters as extending 22224 metres. PiusImpavidus (talk) 11:23, 21 December 2024 (UTC)

Our nautical mile article says: "In 1929 the international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 metres (which is 6,076.12 ft). The United States did not adopt the international nautical mile until 1954. Britain adopted it in 1970..." - Alansplodge 21:53. 21 December 2024

The Wikipaedia article on the Nautical Mile talks about how the term originated, it was originally defined in terms of latitude not as a number of meters 114.75.48.128 (talk) 10:03, 24 December 2024 (UTC)

Question 2

2. There were US dollars in use before there were Euros. - Philvoids 00:52, 21 December 2024

The US dollar has been the world's dominant reserve currency for about 75 years. - Cullen328 02:28, 21 December 2024

The euro is tied to multiple specific countries is it not? If you use euros you're just changing from one "dependency" to a "dependency" on the eurozone countries. A statement of the problem or problems intended to be addressed would be useful. Currency values are interconvertible in any case. Economics does sometimes use the "international dollar" for certain things, which is intended to adjust for differences in purchasing power between countries and over time. But since it's not an actual "real" currency it's not something one can easily "visualize" in their heads, which is likely why it's not used more. --Slowking Man (talk) 05:41, 26 December 2024 (UTC)

Eurostat, the official source of European Union data, uses euros, not dollars, to measure the economy. See ]?DOR (ex-HK) (talk) 01:27, 1 January 2025 (UTC)

The user doubled-down on the response. ←Baseball Bugs carrots→ 01:32, 1 January 2025 (UTC)

Now fixed. 89.243.14.91 (talk) 13:50, 1 January 2025 (UTC)

Question 3

3.Yes.

The questions all reduce to Why can't millions of people make a change of historically widely accepted units that continue to serve their purpose, and convert to different units that would have no substantive difference, because someone has an opinion. Philvoids (talk) 00:52, 21 December 2024 (UTC)

As the US customary units are actually defined in terms that relate them to metric units, any US law based on measurements is technically defined by metric units.--User:Khajidha (talk) (contributions) 01:55, 21 December 2024 (UTC)

As for the metric system in the US, it is standard in scientific, medical, electronics, auto manufacturing and other highly technical industries. By law, all packaged foods and beverages have metric quantities as well as customary quantities. See Metrication in the United States. Cullen328 (talk) 02:28, 21 December 2024 (UTC)

December 24

Unknown species of insect

Am I correct in inferring that this guy is an oriental beetle? I was off-put by the green head at first, but the antennae seem to match. JayCubby 03:00, 24 December 2024 (UTC)

(reference: https://www.genesdigest.com/macro/image.php?imageid=168&apage=0&ipage=1)

It looks like one of the invasive Japanese beetles that happens to like my blackberries in the summer. Modocc (talk) 13:11, 24 December 2024 (UTC)

I would say not necessarily a Japanese beetle, but almost certainly one of the other Scarab beetles, though with 35,000 species that doesn't help a lot. Looking at the infobox illustration in that article, 16. & 17., "Anisoplia segetum" looks very similar, but evidently we either don't have an article or (if our Anisoplia article is a complete list) it's been renamed. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 14:18, 24 December 2024 (UTC)

Yes, it's not the Japanese beetle for this beetle appears to lack its white-dotted fringe although its condition is deteriorated. Its shape is also more or less more slender; and not as round. Modocc (talk) 15:02, 24 December 2024 (UTC)

Perhaps it is the shining leaf chafer Strigoderma pimalis. Shown here. Modocc (talk) 16:09, 24 December 2024 (UTC)

That looks like easily the best match I've seen so far, and likely correct. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 17:09, 24 December 2024 (UTC)

December 25

Mass of oscillating neutrino

From the conservation of energy and momentum it follows that a particle that is not subject to external forces must have constancy of mass.

If I am right, this means that the mass of the neutrino cannot change during the neutrino oscillation, although its flavoring may. Is this written down somewhere? Thank you. Hevesli (talk) 19:24, 25 December 2024 (UTC)

Any (flavored) neutrino that is really observed is a superposition of two or three mass eigenstates. This is actually the cause of neutrino oscillations. So, the answer to your question is complicated. Ruslik_Zero 19:40, 25 December 2024 (UTC)

Important note: particle physicists today generally only ever use "mass" to mean "invariant mass" and never anything else: . Like the term says, invariant mass is well, invariant, it never changes ever, no matter what "external forces" may or may not be involved. Being proper particle-icans and following the standard practice in the field, then, the three neutrino masses are constant values. ..."Wait, three?" Yeah sure, turns out neutrinos come in three "flavors" but each flavor is a mixture of the three possible mass "states". As mentioned, due to Quantum Weirdness we aren't able to get these different states "alone by themselves" to measure each by itself, so we only know the differences of the squares of the masses. Yeah welcome to quantum mechanics.

Richard Feynman: "Quantum mechanics describes nature as absurd from the point of view of common sense. And yet it fully agrees with experiment. So I hope you can accept nature as She is  – absurd." --Slowking Man (talk) 06:06, 26 December 2024 (UTC)

The equation ${\displaystyle E^{2}=(pc)^{2}+\left(m_{0}c^{2}\right)^{2}}$ uses invariant mass m₀ which is constant if E and p are constant. The traveling neutrino has a varying mass mixture of different flavors with different masses. If a mixture of different masses changes, you would expect the resulting mass to change with it. But somehow this does not happen as the neutrino mass mixture changes. These mixture changes cannot be any changes. The changes must be such that the resulting mass of the traveling neutrino remains constant. My question is whether this is described somewhere. Hevesli (talk) 11:16, 26 December 2024 (UTC)

I freely confess I'm uncertain exactly what's being "asked for" or "gotten at" here. Have you looked at the neutrino oscillation article? From it: That is, the three neutrino states that interact with the charged leptons in weak interactions are each a different superposition of the three (propagating) neutrino states of definite mass. Neutrinos are emitted and absorbed in weak processes in flavor eigenstates but travel as mass eigenstates.

What is it that we're "doing" with the energy–momentum relation here? For the neutrino, we don't have a single value of "mass" to plug in for ${\displaystyle m_{0}}$, because we can't "see" the individual mass eigenstates, only some linear combination of them. What you want for describing neutrino interactions is quantum field theory, which is special relativity + QM. (Remember, relativity is a "classical" theory, which presumes everything always has single well-defined values of everything. Which isn't true in quantum-world.) --Slowking Man (talk) 18:41, 26 December 2024 (UTC)

Not all potential evolutions of a linear combination of unequal values produce constant results. Constancy can only be guaranteed by a constraint on the evolutions. Does the fact that this constraint is satisfied in the case of neutrino oscillation follow from the mathematical formulation of the Standard Model, or does this formulation allow evolutions of the mass mixture for which the combination is not constant? If the unequal values are unknown, I have no idea of how such a constraint might be formulated. I think the OP is asking whether this constraint is described somewhere.  --Lambiam 00:51, 27 December 2024 (UTC)

December 27

Low-intensity exercise

If you exercise at a low intensity for an extended period of time, does the runner's high still occur if you do it for long enough? Or does it only occur above a certain threshold intensity of exercise? 2601:646:8082:BA0:CDFF:17F5:371:402F (talk) 20:13, 27 December 2024 (UTC)

Hows about you try it and report back? :) ←Baseball Bugs carrots→ 21:31, 27 December 2024 (UTC)

I wanted to try it just today, but I had to exchange the under-desk elliptical trainer I got for Christmas for a different model with more inclined treadles because with the one I got, my knees would hit the desk at the top of every cycle. Anyway, I was hoping someone else tried it first (preferably as part of a formal scientific study) so I would know if I could control whether I got a runner's high from exercise or not? 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:09, 28 December 2024 (UTC)

Also, sorry for adding to my own question, but here's a related one: is it known whether the length of a person's dopamine receptor D4 (which is inversely correlated with its sensitivity) influences whether said person gets a runner's high from exercise (and especially from low-intensity exercise)? 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:14, 28 December 2024 (UTC)

fastidious organism vs auxotroph

Hi,

What is the difference between an auxotroph and a fastidious organism? It seems to me the second one would have more requirements than the first one, but the limit between the two definitions is rather unclear to me.

Thank you 212.195.231.13 (talk) 23:17, 27 December 2024 (UTC)

I'm not 100% sure, but it seems to me that an auxotroph is a specific type of a fastidious organism. 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:02, 28 December 2024 (UTC)

Symbiosis aside, it would seem that most auxotrophs would be fastidious organisms, but there could be many more fastidious organisms that aren't auxotrophs. Auxotrophs specifically can't produce organic compounds on their own. There are a LOT of organisms that rely on the availability of non-organic nutrients, such as specific elements/minerals. For instance, vertebrates require access to calcium. Calcium is an element; our inability to produce it does not make us auxotrophs.

But perhaps symbiosis would allow an organism to be an auxotroph without being a fastidious organism? For instance, mammals tend to have bacteria in our guts that can digest nutrients that our bodies can't on their own. Perhaps some of those bacteria also assemble certain nutrients that our bodies can't? -- Avocado (talk) 14:27, 28 December 2024 (UTC)

December 28

Paper with wrong enantiomer in a figure

In the following reference:

Quack, Martin; Seyfang, Georg; Wichmann, Gunther (2022). "Perspectives on parity violation in chiral molecules: theory, spectroscopic experiment and biomolecular homochirality". Chemical Science. 13 (36): 10598–10643. doi:10.1039/d2sc01323a. PMID 36320700.

it is stated in the caption of Fig. 8 that S–bromochlorofluoromethane is predicted to be lower in energy due to parity violation, but in the figure the wrong enantiomer is shown on this side. Which enantiomer is more stable, according to the original sources for this data? –LaundryPizza03 (dc̄) 08:18, 28 December 2024 (UTC)

Where can I find data on the circulation and citation rates of these journals?

Hello everyone, To write an article about a scientist, you need to know, where can I find data on circulation and citation rates of journals from this list? Vyacheslav84 (talk) 09:58, 28 December 2024 (UTC)

So-called “Hydrogen water”

I saw an ad promoting a device which presumable splits water into hydrogen and oxygen and infuses water with extra hydrogen, to a claimed surplus of perhaps 5 ppm, which doesn’t seem like much. I found a review article which looked at several dozen related studies that found benefits:https://pmc.ncbi.nlm.nih.gov/articles/PMC10816294/ .

I’ve noticed that carbon dioxide or chlorine (chloramine?) dissolved in water work their way out pretty easily, so I wonder if dissolved hydrogen could similarly exit hydrogen enriched water and be burped or farted out, rather than entering the blood stream and having health benefits. is it more than the latest snake oil? Edison (talk) 23:01, 28 December 2024 (UTC)

Yes, the dissolved hydrogen will exit the water just as quickly (even faster, because of its low molecular mass and complete lack of polarity or capability for ionic dissociation), and even if it does enter the bloodstream, it will likewise get back out in short order before it can actually do anything (which, BTW, is why deep-sea divers use it in their breathing mixes -- because it gets out of the bloodstream so much faster and therefore doesn't build up and form bubbles like nitrogen does) -- so, I don't think it will do much! 2601:646:8082:BA0:209E:CE95:DB32:DD64 (talk) 01:50, 29 December 2024 (UTC)

It's conceivable it might take out the chloramine, I guess. I don't think there's very much of it, but it tastes awful, which is why I add a tiny bit of vitamin C when I drink tap water. It seems to take very little. Of course it's hard to tell whether it's just being masked by the taste of the vitamin C. --Trovatore (talk) 02:12, 29 December 2024 (UTC)

If you just want to split water into hydrogen and oxygen all you need is a battery and two bits of wire. You don't say where you saw this ad but if it was on a socia media site forget it. Shantavira| 11:47, 29 December 2024 (UTC)

If this so-called hydrogen water was emitting hydrogen bubbles, would it be possible to set it afire? ←Baseball Bugs carrots→ 14:03, 1 January 2025 (UTC)

We once had an article on this topic, but see Misplaced Pages:Articles for deletion/Hydrogen water. Graeme Bartlett (talk) 22:27, 1 January 2025 (UTC)

I don't know if it is rubbish or not but a quick look on the web indicates to me it is notable enough for Misplaced Pages. I didn't see anything indicating it definitely did anything useful so such an article should definitely have caveats. I haven't seen any expression of a potential worry either so it isn't like we'd be saying bleach is a good medicine for covid. NadVolum (talk) 23:07, 1 January 2025 (UTC)

International Journal of Molecular Sciences does not sound of exceptionally high quality. DMacks (talk) 01:05, 2 January 2025 (UTC)

December 29

Potential energy vs. kinetic energy. Why not also "potential velocity" vs. "kinetic velocity"? E.g. in the following case:

In a harmonic oscillator, reaching the highest point involves - both a minimal kinetic energy - along with a maximal potential energy, whereas reaching the lowest point involves - both a maximal kinetic energy - along with a minimal potential energy. Thus the mechanical energy becomes the sum of kinetic energy + potential energy, and is a conserved quantity.

So I wonder if it's reasonable to define also "potential velocity" vs. "kinetic velocity", and claim that in a harmonic oscillator, reaching the highest point involves - both a minimal "kinetic velocity" (i.e. involves what we usually call a rest) - along with a maximal "potential velocity", whereas reaching the lowest point involves - both a maximal "kinetic velocity" (i.e. involves what we usually call the actual velocity) - along with a minimal "potential velocity". Thus we can also define "mechanical velocity" as the sum of "kinetic velocity" + "potential velocity", and claim that the mechanical velocity is a conserved quantity - at least as far as a harmonic oscillator is concerned.

Reasonable?

Note that I could also ask an analogous question - as to the concept of "potential momentum", but this term is already used in the theory of hidden momentum for another meaning, so for the time being I'm focusing on velocity.

HOTmag (talk) 12:26, 29 December 2024 (UTC)

'kinetic velocity' is just 'velocity'. 'potential velocity' has no meaning. Andy Dingley (talk) 13:56, 29 December 2024 (UTC)

Per my suggestion, the ratio between distance and time is not called "velocity" but rather "kinetic velocity".

Further, per my suggestion, if you don't indicate whether the "velocity" you're talking about is a "kinetic velocity" or a "potential velocity" or a "mechanical velocity", the very concept of "velocity" alone has no meaning!

On the other hand, "potential velocity" is defined as the difference between the "mechanical velocity" and the "kinetic velocity"! Just as, this is the case if we replace "velocity" by "energy". For more details, see the example above, about the harmonic oscillator. HOTmag (talk) 15:14, 29 December 2024 (UTC)

You could define the potential velocity of a body at a particular height as the velocity it would hit the ground at if dropped from that height. But the sum of the potential and kinetic velocities would not be conserved; rather ${\displaystyle v_{\mathrm {tot} }={\sqrt {v_{p}^{2}+v_{k}^{2}}}}$ would be constant. catslash (talk) 18:54, 29 December 2024 (UTC)

Thank you. HOTmag (talk) 20:07, 29 December 2024 (UTC)

'Potential velocity' has no meaning. You seem to be arguing that in a system where energy is conserved, but is transforming between kinetic and potential energy, (You might also want to compare this to conservation of momentum.) then you can express that instead through a new conservation law based on velocity. But this doesn't work. There's no relation between velocity and potential energy.

In a harmonic oscillator, the potential energy is typically coming from some central restoring force with a relationship to position, nothing at all to do with velocity. Where some axiomatic external rule (such as Hooke's Law applying, because the system is a mass on a spring) happens to relate the position and velocity through a suitable relation, then the system will then (and only then) behave as a harmonic oscillator. But a different system (swap the spring for a dashpot) doesn't have this, thus won't oscillate. Andy Dingley (talk) 00:00, 30 December 2024 (UTC)

Let me quote a sentence from my original post: Thus we can also...claim that the mechanical velocity is a conserved quantity - at least as far as a harmonic oscillator is concerned.

What's wrong in this quotation? HOTmag (talk) 07:52, 30 December 2024 (UTC)

It is true, not only for harmonic oscillators, provided that you define v_pot = − v_kin.  --Lambiam 09:07, 30 December 2024 (UTC)

• You have defined some arbitrary values for new 'velocities', where their only definition is that they then demonstrate some new conservation law. Which is really the conservation of energy, but you're refusing to use that term for some reason.

As Catslash pointed out, the conserved quantity here is proportional to the square of velocity, so your conservation equation has to include that. It's simply wrong that any linear function of velocity would be conserved here. Not merely we can't prove that, but we can prove (the sum of the squares diverges from the sum) that it's actually contradicted. For any definition of 'another velocity' which is a linear function of velocity.

Lambiam's definition isn't a conservation law, it's merely a mathematical identity. The sum of any value and its additive inverse is always zero. Andy Dingley (talk) 14:04, 30 December 2024 (UTC)

It is a law of conservation of sanity. Lacking a definition of potential energy, other than by having been informed that kinetic energy + potential energy is a conserved quantity, there is not much better we can do.  --Lambiam 11:20, 31 December 2024 (UTC)

We have a perfectly viable definition of potential energy. For a pendulum it's based on the change in height of the pendulum bob against gravity. For some other oscillators it would involve the work done against a spring. Andy Dingley (talk) 16:33, 31 December 2024 (UTC)

Oops, I mistyped. I meant to write:

"Lacking a definition of potential velocity, other than by having been informed that kinetic velocity + potential velocity is a conserved quantity, there is not much better we can do."

 --Lambiam 23:32, 31 December 2024 (UTC)

December 30

Saltiness comparison

Is there some test one might easily perform in a home test kitchen to compare the saltiness (due to the concentration of Na cations) of two liquid preparations, without involving biological taste buds?  --Lambiam 09:22, 30 December 2024 (UTC)

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)

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)

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)

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)

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)

That's what I'm thinking too -- use an ohmmeter to measure the electrical conductivity of the preparation, and compare to that of solutions with known NaCl concentration (using a calibration curve-type method). 73.162.165.162 (talk) 20:18, 31 December 2024 (UTC)

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)

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".  --Lambiam 11:40, 2 January 2025 (UTC)

The (uncommon?) terms "relativistic length", and "relativistic time".

1. In Misplaced Pages, 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"?

HOTmag (talk) 09:32, 30 December 2024 (UTC)

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)

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 Misplaced Pages), 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.

Anyway, I'm still waiting for an answer to my original question: Are there accepted terms for the concepts, of relativistic length - as opposed to proper length, and of relativistic time - as opposed to proper time? HOTmag (talk) 10:12, 30 December 2024 (UTC)

A term that will be understood in the context of relativistic length contraction is relative length – that is, length relative to an observer.  --Lambiam 10:55, 31 December 2024 (UTC)

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)

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.

A similar use of "relative length" can be seen on the preceding page.  --Lambiam 10:23, 2 January 2025 (UTC)

What did Juan Maldacena say after "Geometry of" in this video?

I was watching this video Brian Greene and Juan Maldacena as they explore a wealth of developments connecting black holes, string theory etc, Juan Maldacena said something right after "Geometry of" Here is the spot: https://www.youtube.com/live/yNNXia9IrZs?si=G7S90UT4C8Bb-OnG&t=4484 What is that? HarryOrange (talk) 20:46, 30 December 2024 (UTC)

Schwarzschild solution. --Wrongfilter (talk) 21:05, 30 December 2024 (UTC)

Thank you, its the Juan Maldacena's accent which made me post here. HarryOrange (talk) 21:18, 30 December 2024 (UTC)

December 31

Brightest spot of a discharge tube

What causes the discharge tubes to have their brightest spots at different positions? Nucleus hydro elemon (talk) 13:12, 31 December 2024 (UTC)

See also the pictures at Gas-filled tube #Gases in use. --CiaPan (talk) 13:26, 31 December 2024 (UTC)

January 1

Two unit questions

1. 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"?
2. Is a one-tenth of nautical mile (185.2 m) used in English-speaking countries? Is there a name for it?

--40bus (talk) 10:41, 1 January 2025 (UTC)

1 not that I know of (engineer who has worked with SI for 50 years)

2 not that I know of (yacht's navigator for many years on and off)

Greglocock (talk) 11:35, 1 January 2025 (UTC)

In Finland, kaapelinmitta is 185.2 m. Is there an English equivalent? --40bus (talk) 18:11, 1 January 2025 (UTC)

Cable length. --Wrongfilter (talk) 18:26, 1 January 2025 (UTC)

Good article. I was wrong Greglocock (talk) 22:26, 1 January 2025 (UTC)

The answer can be found by looking up kaapelinmitta on Wiktionary.  --Lambiam 00:14, 2 January 2025 (UTC)

What is more physiological (for a right-hander) left-hand drive or right-hand drive?

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)

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)

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)

In the UK nowadays, are cars still mostly manual transmission, or has automatic become the norm? ←Baseball Bugs carrots→ 12:38, 2 January 2025 (UTC)

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)

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)

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.

--Lambiam 16:30, 2 January 2025 (UTC)

Distinguishing a picture of a sunset from the picture of a sunrise?

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)

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)

January 2

• Misplaced Pages resources for researchers
• Misplaced Pages help forums
• Misplaced Pages reference desk