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December 7

Can you have an electromagnetic pulse without a planetary magnetic field?

(Electromagnetic pulse) Say on Venus, Mars or Titan. JoJo Eumerus mobile (main talk) 20:14, 7 December 2022 (UTC)

Yes. --OuroborosCobra (talk) 22:38, 7 December 2022 (UTC)

EMPs caused by lightning can occur on planets with an atmosphere, such as Venus. The EMP carried by a powerful coronal mass ejection can certainly impact all inner planets but will not cause a magnetic storm on those without magnetosphere. BTW, Titan's orbit skirts Saturn's magnetosphere, and a magnetic storm on Saturn might have a minor influence there.  --Lambiam 03:57, 8 December 2022 (UTC)

Are there any papers or books discussing such a non-magnetic EMP? Jo-Jo Eumerus (talk) 10:53, 8 December 2022 (UTC)

EMP stands for electromagnetic pulse; they are as magnetic as it gets with pulses. Various types, distinguished by what causes them, are discussed in our article on this topic, which you linked to in the question.  --Lambiam 12:04, 8 December 2022 (UTC)

Just to clarify, electromagnetism is one thing. If you have moving electrical charges, you're going to have a magnetic field. If you have a magnetic field, there's a moving charge of some sort. Insofar as lightning is an electric current, it will generate a magnetic field. --Jayron32 13:08, 8 December 2022 (UTC)

Sorry, should have said "EMP on a body w/o an intrinsic magnetic field". Jo-Jo Eumerus (talk) 15:11, 8 December 2022 (UTC)

@Jo-Jo Eumerus:, you seem to be under a false impression of some sort, though I'm not entirely sure what. The existence of magnets, magnetism, and magnetic fields does not depend upon a planet having a magnetic field. If you take a permanent magnet from Earth and take it to Mars, it will still be a magnet and still have a magnetic field. If you take an electromagnet to Mars and turn it own (moving electrical charges through it), you will have a magnetic field. Second, an EMP is not a pulse of or through a planetary magnetic field. If you detonate a nuke on Mars, you will have an EMP. It's being generated by the nuke itself, and not an interaction with a planetary magnetic field. To put it another way, water is still wet on Mars, as it being wet is a property of water, and not the planet it is on. In either case, the existence (or absence) of "a body" with "an intrinsic magnetic field." --OuroborosCobra (talk) 14:59, 8 December 2022 (UTC)

As listed in the linked article, there are many kinds of electromagnetic pulses, differing in strength, spectrum, polarisation and cause. A nuclear electromagnetic pulse caused by a high-altitude nuclear detonation like the Starfish Prime test has a lot to do with the planetary magnetic field. It's horizontally polarised and very fast (nanoseconds). Your average nuclear detonation at ground level also causes an EMP, much weaker, and vertically polarised. That pulse doesn't depend on the magnetic field. A coronal mass ejection hitting the Earth's magnetosphere can cause a geomagnetic storm, a kind of EMP over a billion times slower than the nuclear kind (seconds to minutes) and with completely different effects. That pulse also depends on a planetary magnetic field. A lightning strike makes a pulse on an intermediate timescale (milliseconds) and doesn't depend on the planetary magnetic field. PiusImpavidus (talk) 17:14, 8 December 2022 (UTC)

Sugar solubility in sodium chloride solutions

What data are available re the solubility of sucrose in sodium chloride solutions of various salt content up to saturation in salt, compared to the solubility of sucrose in pure water? Is there salting-in or salting-out? 178.138.99.84 (talk) 23:53, 7 December 2022 (UTC)

"It's complicated as hell." See:

• Seidell, Atherton (1919). Solubilities of Inorganic and Organic Compounds. p. 694.

for a table of "solubility of sugar in aqueous salt solutions at 30°, 50°, and 70°". It in turn is cited to original data from page 313 of:

• Schukow, Iwan (1900). "On the influence of temperature on the solubility of the sugar in solutions of non sugars". Zeitschrift des Vereines der Deutschen Zucker-Industrie. 50: 291–321.

Wow, that was a fun fragment of a ref to decipher and trace! I think there may be a sub-title to that journal, as it has merged and split several times. DMacks (talk) 02:15, 8 December 2022 (UTC)

So, diving down a rabbit-hole, I could find only limited information about Schukow, so we won't get a new bio article from him. Apparently he was involved with the Association of Russian Sugar Manufacturers. I found proceedings of a 1906 meeting he attended where others were discussing ongoing development and validation of a fancy then-new test called Fehling's solution. That discussion also mentioned the name Violett in connection with that sort of reagent, but I'm at a dead-end finding any further info in that direction. Does anyone know if Violett is someone who involved with Fehling's (but whose name fell out of eponymous use) or if it is a different reagent that has itself long become obsolete? DMacks (talk) 05:08, 8 December 2022 (UTC)

The Ukrainian and Russian Wikipedias each have an article on Ivan Diomydovych Zhukov: uk:Жуков Іван Діомидович and ru:Жуков, Иван Диомидович.  --Lambiam 11:53, 8 December 2022 (UTC)

Thanks! Anglicizing those names from older literature makes my brain hurt. DMacks (talk) 16:59, 8 December 2022 (UTC)

It is not a matter of age, but merely of a different method of Romanization for German as the target language. "Our" Georgy Konstantinovich Zhukov is Georgi Konstantinowitsch Schukow on the German Wikipedia.  --Lambiam 21:16, 8 December 2022 (UTC)

Is it possible that the word Violett was the German term for the colour violet?  --Lambiam 16:16, 10 December 2022 (UTC)

No, Graeme Bartlett tracked down the source as Violette's solution. It is copper sulfate, rochelle salt and caustic soda in water, similar to Fehling's solution. Mike Turnbull (talk) 16:40, 10 December 2022 (UTC)

December 8

Water boiled twice

I've heard that water tastes different after being boiled a second time because all dissolved oxygen has been boiled off. Is there any truth to that? 31.217.44.13 (talk) 05:07, 8 December 2022 (UTC)

Why don't you try it for yourself, and report your findings here? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:33, 8 December 2022 (UTC)

Fortunately, somebody has already done that, see:

Quality change mechanism and drinking safety of repeatedly-boiled water and prolonged-boil water: a comparative study, which says:

The quality changes of RBW [repeatedly-boiled water] and PBW [prolonged-boil water] show very similar trends that are not as great as might be imagined, and both are impacted by the tap water quality and the physiochemical effects. The dominating physiochemical effects are the water evaporation and the resulting concentration of unreactive components (most dissolved components), which can be easily explained by the existing evaporation-concentration theory.

So any slight change in taste is due to the concentration of minerals and other impurities, caused by evaporation.

Alansplodge (talk) 12:16, 8 December 2022 (UTC)

• See this previous question: Wikipedia:Reference desk/Archives/Science/2010 February 23#Making tea with zingless water. -- Jack of Oz ^{[pleasantries]} 19:50, 8 December 2022 (UTC)

Well remembered Jack. It comes to a similar conclusion but without citing a source. Alansplodge (talk) 22:20, 8 December 2022 (UTC)

It's wrong to say as in that thread that re-boiled water is harmful. People choose not to do it for taste, not health, reasons. 74.64.73.24 (talk) 21:39, 10 December 2022 (UTC)

That's pretty interesting! I can't see any difference in taste but have always thrown it out because boiling the second time won't produce bubbles but dislodges lime chunks. Tap water is very hard here (tastes like evian) but not chlorinated, still I'd rather not get chunks of carbonate in my food & drink (its taste doesn't go well with anything). 31.217.44.13 (talk) 15:15, 9 December 2022 (UTC)

Implausible sung note

Our article on Tim Storms alleges that he has sung a note of G₋₇, or 0.189 Hz, at which pitch it would need "more than five seconds for the vocal cords to oscillate once".

I'm curious in what sense this can be said to be "singing". What if I just breathe in for 2.5 seconds and out for the same length of time? Am I not generating 0.2 Hz pressure waves, at very low intensity to be sure, but probably more than Storms is getting from his vocal folds? And given that he has time to consciously reshape his larynx during a single cycle, why couldn't anyone do that?

I suspect there's some sense in which the claim is meaningful, but I'm having trouble figuring out what it could be. --Trovatore (talk) 16:35, 8 December 2022 (UTC)

I agree. A 0.2 Hz sound isn't a note, it's percussion. You generate a sound like that merely by hitting a drum every 5 seconds. The effect on the listener would not be a note, but of slowly repeated pulses. Even in the case of a long attack and decay, such a sound would not be recognizable as a pitch. The relationship between rhythm and pitch (which is to say that pitch is just rhythm sped up) is demonstrated to great effect in this video starting at 4:23 by Adam Neely during a lecture he gave a few years back. 12 bpm is even fantastically slow for a practical rhythm, Neely himself makes the case that 33 bpm is the slowest reasonable rhythm for anything described as music. See [1]. --Jayron32 16:46, 8 December 2022 (UTC)

Why is it that if a robot pops bubble wrap at precisely 1,201 beats per minute it makes a continuous note (at least if the bubble to left ear and bubble to right ear travel times are two constants x and y) but the inventor of the sea clock could hear second ticks weren't simultaneous till they were ≤0.02 seconds apart? He'd keep a prototype on each side of the door in the winter to test how long it took the cold one to drift 1 second and in the middle 96/100ths of this time he could tell it didn't sound like when it was simultaneous. Sagittarian Milky Way (talk) 23:57, 8 December 2022 (UTC)

These are quite different scenarios. They can coexist. One is about a rapid steady repetition being perceived as a tone, a quality of the sound. (Does the number 1,201 have a particular significance, or might you as well have written 20 Hz?) The other is about limitations in perceiving differences. What makes you think that this coexistence is in need of an explanation?  --Lambiam 05:02, 9 December 2022 (UTC)

SMW: If you watch the Neely videos like I told you, he actually demonstrates it. In the range between about 10-20 Hz, the sound becomes "confused" and people have a functionally hard time distinguishing between pitch and rhythm. It also is not a hard limit across humanity. In those ranges, different people will "hear" different things depending on factors entirely unique to themselves; but generally pulses below 10 Hz generally are perceived as individual beats (rhythm) and generally pulses above 20 Hz are perceived as pitch, but these are not hard-and-fast. This also depends on the exact characteristics of the sound wave in complex ways. A sawtooth wave and a square wave and a sinusoidal wave will all probably have distinctly different ranges over which they get perceived as separate pulses vs. pitches. Also also, there is a complex perceptive relationship between amplitude and frequency and perceived loudness; generally higher pitched sounds are perceived as higher in volume for the same actual amplitude waves; this is why infrasound is a thing. If you take a note at a certain consistent amplitude, and lower the pitch, it becomes progressively quieter and quieter until it becomes inaudible. Infrasound of the same amplitude as most audible pitches is inaudible to most human ears. If you raise the volume on those sounds, however, to the point where we can hear them, they will sound like individual pulses rather than as a distinct pitch; at least until about the 10 Hz limit... after which it becomes confusing until about 20 Hz. --Jayron32 12:58, 9 December 2022 (UTC)

I can sing at 1.6 μHz, but when I tried to demonstrate that to the Guinness Book of World Records judges, they got impatient and left even before I had gone through the first cycle.  --Lambiam 05:08, 9 December 2022 (UTC)

In acoustics, we have the concept of timbre. A musical note is embodied by a complex sound wave carrying energy at many frequencies, with one prominent fundamental frequency. Perhaps non-obviously, the fundamental frequency need not be the most energetic: if we plot the spectrogram for most musical instruments (and especially for the human voice), we can easily see that even a simple note has many frequencies. We have technical words for some of these aspects: overtones, timbre, resonance, and so on. But it's complicated - it's worthy of an entire library full of explanatory books.

To try to make some sense of it, Here's Fundamental Frequencies, part of the Real Simple Project in computational acoustics at CCRMA, "devoted to the development of musical acoustics laboratory exercises integrating both hands-on laboratory experience and computer-based simulation." If you want to play with Fourier analysis of musical tones, this website provides great resources at zero cost - and it ramps up in mathematical complexity to serve the needs of even the most mathematically analytical signal-processing and music enthusiast!

Just to layer on some complexity, there exist plenty of situations where the sound wave contains zero energy at its fundamental frequency - for certain defintions of the fundamental frequency - because the fundamental frequency can be defined using the spacing of the harmonics, rather than the value of the lowest harmonic. This means that the fundamental need not be the lowest frequency that contains energy, either! This stuff isn't only theoretical nonsense - it has a lot to do with how a human perceives the musical note embodied in a complex waveform. This was demonstrated as a sort of party-trick during a recent episode of QI: identical complex tones were played, and the panelists were asked which notes sounded higher - when in fact this was a soundwave with frequencies specifically constructed to create an ill-posed question! (Addendum: this tone experiment was in Series S Episode 6, Sensational! originally aired on 14 October 2021, also described in this unofficial episode guide. This is the "tritone paradox" and it is has been heavily studied - for decades!)

For "very low frequency" signals - one of my personal favorite topics - the theory can be quite clear, but the signal can be very muddy!

Nimur (talk) 16:30, 9 December 2022 (UTC)

This is also one of those cases where how a physicist defines something differs from how a lay person may define it. All mechanical waves are sound and operate essentially identically regardless of frequency. Human perception on treats a narrow swathe of possible mechanical waves as audible, and human perception also treats different ranges of frequencies within that range differently (see above on the difference between rhythm and pitch). This is almost exactly analogous to the human perception of light, where the visible spectrum is a tiny slice of the range of frequencies of electromagnetic radiation. Humans tend to think of the color yellow as somehow a different phenomenon than, say, their local radio broadcast. It isn't though. They're both just light, though vibrating at different frequencies. Same thing here, whether it is an earthquake or a pulsing drumbeat or a the F above middle C, it's all the same sort of thing. --Jayron32 17:10, 9 December 2022 (UTC)

Also to Nimurs point about fundamental frequency, timbre, and the overtone series, the low notes on a bass instrument, like a bass guitar generally have fundamental frequencies that lie near the limit of human perception. At the amplitudes normally played by such an instrument, the actual fundamental frequency on, say, the low-B string on a 5-string bass probably lies well outside the limit of human perception, unless the instrument is really loud. And yet, our brains do some pretty neat stuff with the overtone series; in with all of the overtones, we will tend to "hear" fundamental frequencies that if played by themselves as a pure sine wave, we would only slightly detect (or maybe not at all, depending on our perception of loudness of that frequency) and yet when played on a bass, our brain "hears" that frequency by "filling in the gaps". Basically, as a psychoacoustics effect, our brain is capable of psychologically "boosting" the lower notes in the context of the overtones. This is also apparent in sound systems that use a subwoofer. When played by itself, a subwoofer often only sounds like a muffled, indistinct, low-frequency sound which is hard to resolve. When played along side of the rest of the sound system, the bass notes become crisper and easier to resolve, however, because when you hear the bass in context of its overtones, your brain is able to better "latch on" to that low sound and resolve it better. --Jayron32 17:20, 9 December 2022 (UTC)

Also also, there's a whole article on this sort of thing at Missing fundamental. --Jayron32 17:22, 9 December 2022 (UTC)

MF is a psychoacoustic effect. If you run an FFT analysers on it the fundamental is missing. In the less interesting case of making a noise that measures 0.2 Hz, anybody can do it as many have posited. Guinness book of records has about as much credibility in the scientific world as Budweiser does in the non American beer world. Greglocock (talk) 05:12, 10 December 2022 (UTC)

Yes, I believe when I said "as a psychoacoustics effect" what I meant was that it was a psychoacoustics effect. Sorry that was confusing to you. Did I clear it up? --Jayron32 12:58, 12 December 2022 (UTC)

December 10

Maxwell's third and fourth equations

Using Formulation in SI units convention and ignoring the conventional current term of Ampere-Maxwell equation (focusing solely on the displacement current term), we have: ${\begin{aligned}\oint _{\partial \Sigma }&\mathbf {B} \cdot \mathrm {d} {\boldsymbol {\ell }}==\mu _{0}\varepsilon _{0}{\frac {\mathrm {d} }{\mathrm {d} t}}\iint _{\Sigma }\mathbf {E} \cdot \mathrm {d} \mathbf {S} \\\end{aligned}}$

So my question is: why is the Maxwell-Faraday equation in the following form: $\oint _{\partial \Sigma }\mathbf {E} \cdot \mathrm {d} {\boldsymbol {\ell }}=-{\frac {\mathrm {d} }{\mathrm {d} t}}\iint _{\Sigma }\mathbf {B} \cdot \mathrm {d} \mathbf {S}$ and not in the following form: $\oint _{\partial \Sigma }\mathbf {E} \cdot \mathrm {d} {\boldsymbol {\ell }}=-\mu _{0}\varepsilon _{0}{\frac {\mathrm {d} }{\mathrm {d} t}}\iint _{\Sigma }\mathbf {B} \cdot \mathrm {d} \mathbf {S}$ ?

Many thanks, 173.209.130.10 (talk) 21:29, 10 December 2022 (UTC)

The units wouldn't match. The SI unit of the electric field is $[E]=1\,\mathrm {\frac {N}{As}}$, of the magnetic field $[B]=1\,\mathrm {\frac {N}{Am}}$. With that the unit of the left hand side is $\mathrm {{\frac {N}{As}}\cdot m} =\mathrm {\frac {Nm}{As}}$, of the right hand side it is $\mathrm {{\frac {1}{s}}{\frac {N}{Am}}\cdot m^{2}} =\mathrm {\frac {Nm}{As}}$, i.e. the same, as it must be. The factor $\varepsilon _{0}\mu _{0}=1/c^{2}$ with unit $\mathrm {\frac {s^{2}}{m^{2}}}$, and if you insert that as you propose, you mess up the units of the right hand side. --Wrongfilter (talk) 21:47, 10 December 2022 (UTC)

Using natural units in which $c=1,$ the identities take on a more symmetric appearance.  --Lambiam 05:13, 11 December 2022 (UTC)

December 11

When a high-speed alpha particle hits a gold nucleus, does the gold nucleus remain stationary?

In the Geiger-Marsden experiments, the alpha particle can receive the entire changes of momentum if the gold nucleus remains stationary.

$\Delta p=F\Delta t=k\cdot {\frac {Q_{\alpha }Q_{n}}{r^{2}}}\cdot {\frac {2r}{v_{\alpha }}}$

Otherwise, the KE gained by the gold nucleus must equal the KE lost by the alpha particle. Vze2wgsm1 (talk) 12:29, 11 December 2022 (UTC)

It's not at all clear what your question is. The equation you've posted IS the change of momentum in the alpha particle under a classical mechanical description of the collision as an elastic one between two spheres. There is ALSO a change in momentum of the gold atom, and a corresponding change in kinetic energy of each. And yes, as long as you consider this an elastic collision, then kinetic energy is conserved. PianoDan (talk) 18:03, 11 December 2022 (UTC)

Rutherford's gold foil experiment, performed by Geiger-Marsden, is the basis of believing an atom has a nucleus. Rutherford used the above equation to claim that an alpha particle collision with a gold nucleus can reverse the alpha particle's momentum. In other words, Rutherford may have made a false assumption. The alpha particle's deflection by more than 90 degrees may have been via collision with a multi-atom molecule, instead of a collision with the nucleus of a single gold molecule. Vze2wgsm1 (talk) 22:46, 11 December 2022 (UTC)

Gold molecules? Au₃O₄? Given a model for the atom, one can compute the predicted distribution of the angles of deflection of the emerging alpha particles. This is not about the occasional stray particle, but about substantial numbers. If the observations differ too strongly from the theoretical model, and experimental or calculation errors can be ruled out, the model was wrong.  --Lambiam 01:46, 12 December 2022 (UTC)

The calculation predicting the angles of deflection assume that gold nucleus (q_n) remains stationary while the alpha particle approaches and leaves the gold nucleus.

$s={\frac {Xnt\csc ^{4}{\!\left({\tfrac {\phi }{2}}\right)}}{16r^{2}}}\cdot {\left({\frac {2Q_{n}Q_{\alpha }}{mv^{2}}}\right)}^{2}$

Acceleration of q_n removes KE from the alpha particle and changes the angle of deflection Vze2wgsm1 (talk) 02:47, 12 December 2022 (UTC)

I don't get what you are trying to argue, other than that you seem to think Rutherford and his team (and the many teams who replicated the experiment) were stupid and overlooked something big, like the presence of Blue Meanies imparting motion to the gold nuclei.  --Lambiam 05:18, 12 December 2022 (UTC)

If you think that Rutherford's calculations of alpha particle deflection do not assume a stationary gold nucleus, then either mathematically prove your point, or show how a gold nucleus can indeed remain stationary while a high-speed alpha particle approaches. I wish you luck. Vze2wgsm1 (talk) 09:54, 12 December 2022 (UTC)

It's called an approximation, and it's made because a gold nucleus is about 50 times as massive as an alpha particle. Do you think that approximation is unjustified and therefore everything we know about atoms and nuclei is wrong? Because nobody's done any more experiments since Geiger-Marsden? Or done any more sophisticated analysis of scattering experiments than Rutherford in the last hundred years? --Wrongfilter (talk) 10:17, 12 December 2022 (UTC)

Thanks PianoDan. I appreciate your comment on the equation. Another equation from the Geiger-Marsden experiments article indicates the alpha particle receives the entire change of momentum when an alpha particle approaches a gold nucleus. When a high-speed alpha particle hits a gold nucleus, does the gold nucleus remain stationary?

$::\theta \approx {\frac {\Delta p}{p}}<k\cdot {\frac {2Q_{\alpha }Q_{n}}{m_{\alpha }rv_{\alpha }^{2}}}::$ Vze2wgsm1 (talk) 11:39, 12 December 2022 (UTC)

It remains stationary enough. Remember a couple of things about the transfer of momentum of the alpha particle to the gold atoms in the experiment 1) the alpha particle is 1/50 the size of the gold nucleus, so that needs to be taken into account. But MOST IMPORTANTLY, 2) the gold atoms are bound up in a solid crystal lattice. Yes, if the gold atoms were in the gas phase, we would expect a transfer of kinetic energy on something like a one-to-one relationship. However, the gold atoms are bound up with each other in a solid matrix. What that means effectively is that the transfer of energy is distributed across the entire sheet of gold foil rather than to 1 gold atom. A single alpha particle, even a really fast moving alpha particle, transferring some of its momentum to trillions upon trillions of gold atoms has essentially no effect on the gold. We can treat the gold atoms as stationary, because they essentially are; any displacement of the gold nucleus by interaction with an alpha particle is so many orders of magnitude smaller than the size of the nucleus itself, it is functionally nil. --Jayron32 12:56, 12 December 2022 (UTC)

I'm not so sure about the lattice argument. Atoms in a crystal do oscillate about their mean positions, and a collision will excite crystal vibrations (phonons on a quantum level). The transferred energy will ultimately dissipate away, and the momentum transfer to the entire gold foil is obviously negligible, but that does not make it necessarily so in the individual scattering process, which is what is relevant here. I'm not well versed in crystal and solid state physics, but my gut feeling suggests that it ought to be more appropriate to treat the gold nuclei as free particles rather than being fixed in a crystal lattice (actually, do nuclei know that they live in a crystal?). Which brings us back to the mass ratio of 50 that again makes a stationary gold nucleus a good approximation. --Wrongfilter (talk) 14:57, 12 December 2022 (UTC)

Yes, but the important thing is it will not excite one single atom alone; such excitations are dispersed through the lattice of gold atoms. The OP sounds like their major objection is that the fact that when interacting with the alpha particle, the singular gold atom would experience some kind of measurable displacement in order to itself redirect the alpha particle; the fact that the specific gold atom does not itself appreciably change momentum means that something is wrong with Rutherford's theory. I was explaining why that was at fault; the momentum transferred to any one gold atom is dissipated through the system via the chemical bonds between gold atoms; yes that dissipation does all sorts of complex things to the lattice of gold atoms; but that's irrelevant. The OP's statement "Rutherford used the above equation to claim that an alpha particle collision with a gold nucleus can reverse the alpha particle's momentum" is based on some sort of model of the gold nucleus as a gas particle of some sort, the assumption the OP makes is that Rutherford's model presupposes the gold nucleus absorbs the alpha particle's momentum without itself doing anything with that momentum, violating the law of conservation of momentum. This assumption on the part of the OP seems to be that the interacting gold nucleus is not dissipating the absorbed momentum through the lattice (in all the ways I glossed over but that you describe). That's what they are not understanding here. That's why the gold nucleus remains stationary; or at least can be treated like it remains stationary, even if at levels below the level of measurement, it probably does shimmy a little bit.--Jayron32 15:23, 12 December 2022 (UTC)

I still disagree: the dissipation happens on a time scale that is longer than the time scale that is relevant for the individual scattering process. Staying classical (and we'd need to get quantitative to see whether that is justified), in my view the nucleus ought to be treated as a free particle which does absorb a bit of momentum (not enough to significantly alter Rutherford's conclusions, mind!). This is then transferred to the electron shell of the atom and then to the lattice as a whole. But when this happens the alpha particle is already on its way and is not affected any more. For the time scales I'd look at the speed of the alpha particle vs. the sound speed in the crystal. --Wrongfilter (talk) 15:35, 12 December 2022 (UTC)

That's fair. I concede. Still, it is perplexing that, for the second time in as many weeks, the OP thinks that with almost no in-depth reading of the physics involved in the Rutherford/GM experiment and its conclusions, they're somehow going to play "gotcha" and take down over 100 years of atomic theory so simply. --Jayron32 16:12, 12 December 2022 (UTC)

I'll also point out that if atoms don't have nuclei, then I'm out of a job, since I work in nuclear medicine, and my entire livelihood is based on confirming every single day that our understanding of the nucleus is more or less correct. :) PianoDan (talk) 15:31, 12 December 2022 (UTC)

How do you define nucleus and what is your best evidence that an atom has a nucleus? If you define nucleus as the thing that is left over after all electrons are stripped away from an atom, then I agree with you. The thing that is left over can have volume and chemical reactivity of an atom or molecule.

If you define nucleus as a small structure within an atom, then I wonder how adding a single electron to a stripped nucleus can convert the stripped 'nucleus' into a small structure within an atom? Vze2wgsm1 (talk) 13:27, 13 December 2022 (UTC)

Thanks Jayron32. The gold can ionize, which is an inelastic collision. Typical of high-speed alpha particle collisions. Vze2wgsm1 (talk) 21:56, 12 December 2022 (UTC)

Thanks Jayron32. When an alpha heads toward a stationary gold, and if both the gold and the alpha are free, then during every instant, and at every distance between them, the repulsive force between the alpha and the gold is EQUAL and mutual.

$m_{1}a_{1}=m_{2}a_{2}$

The mutual force causes the KE lost by the alpha to equal the KE gained by the gold, regardless of the difference in mass. The alpha simply loses KE. Vze2wgsm1 (talk) 20:42, 12 December 2022 (UTC)

That is simply Newton's third law of motion. PianoDan (talk) 21:20, 12 December 2022 (UTC)

The point is that a high-speed alpha will not reverse direction when the alpha approaches a free gold nucleus, regardless of the difference between alpha mass and gold mass. Rutherford had to assume a stationary gold, to get Newton's third to reverse the direction of the alpha. Vze2wgsm1 (talk) 05:38, 13 December 2022 (UTC)

Yes, it will reverse direction. Let's look at the one-dimensional problem, central collision of point particles, forward or backward scattering only. We need to satisfy conservation of momentum and of energy, and we write the energies and momenta before and after the collision at infinite separation (large enough that the Coulomb energy is negligible). First, momentum:

$m_{\alpha }v_{i}=m_{g}v_{g}+m_{\alpha }v_{f}$, i.e. $v_{g}=r(v_{i}-v_{f})$,

where I've defined the mass ratio $r=m_{\alpha }/m_{g}\approx 1/50$. Now for energy (the factors 1/2 cancel, and I won't bother to write them out):

$m_{\alpha }v_{i}^{2}=m_{g}v_{g}^{2}+m_{\alpha }v_{f}^{2}$.

Inserting $v_{g}$ and rearranging gives the quadratic equation

$(r+1)v_{f}^{2}-2rv_{i}v_{f}+(r-1)v_{i}^{2}=0$.

This has two solutions. The first is $v_{f}=v_{i}$ and $v_{g}=0$, which corresponds to no collision, this is uninteresting. The second solution is

$v_{f}={\frac {r-1}{r+1}}v_{i}$, hence $v_{g}={\frac {2r}{r+1}}v_{i}$.

With $r\approx 1/50$, the velocity $v_{f}$ of the alpha particle is negative, i.e. reversed. The velocity of the gold nucleus is $v_{g}\approx 0.039v_{i}$, so it does pick up a bit of velocity, which is of course reflected in the fact that the speed of the alpha particle is a bit lower than initally, $|v_{f}|<|v_{i}|$, but clearly in the opposite direction. This is very basic physics. --Wrongfilter (talk) 11:31, 13 December 2022 (UTC)

@Wrongfilter's analysis is correct. And if you want to just visualize it - if you put a bowling ball on an ice covered pool table and hit the cue ball towards it, would you REALLY be surprised if the cue ball came back towards you? Because that is more or less exactly what is happening here. And yes, the bowling ball DOES move a bit away from you in that case. PianoDan (talk) 17:14, 13 December 2022 (UTC)

Thanks Wrongfilter.

1. KE is conserved, due to conservation of energy. Momentum is not necessarily conserved.

2. If gold is free and initially stationary, then the KE lost by the alpha will equal the KE gained by the gold, regardless of the difference in mass. If alpha KE somehow became zero (before reversing direction), then the gold would contain total KE. Afterwards, adding KE to the alpha requires removing KE from the gold.

3. If gold remains stationary, then when the alpha particle slows to zero (before accelerating in the opposite direction) total KE equals zero. Vze2wgsm1 (talk) 22:11, 13 December 2022 (UTC)

Momentum is, in fact, necessarily conserved. TOTAL energy is also conserved. If this were an elastic collision between two solid spheres, then kinetic energy would also be conserved at all times, yes. In that (simplified) model, you would have an instantaneous transfer of (some) energy from the alpha particle to the gold nucleus at the moment of collision, and an instantaneous change of direction.

Worth pointing out, however, that in the nuclear case, there is also POTENTIAL energy to be considered, in the form of the Electric potential energy between the positively charged alpha particle and nucleus, which stores energy as the two particles approach, and returns it to the two particles as they separate. PianoDan (talk) 23:01, 13 December 2022 (UTC)

Thanks PianoDan.

1. Conservation of momentum requires an environment not acted on by external force. The electrostatic force between the alpha and the gold is an external force.

2. Nobody assumed collisions or other instantaneous changes of direction. Electrostatic repulsions are not necessarily collisions.

"If this were an elastic collision between two solid spheres, then kinetic energy would also be conserved at all times, yes. In that (simplified) model, you would have an instantaneous transfer of (some) energy from the alpha particle to the gold nucleus at the moment of collision, and an instantaneous change of direction."

3. You do realize that Rutherford's calculations are based on the electric potential energy between an alpha particle and a gold nucleus.

"there is also POTENTIAL energy to be considered, in the form of the Electric potential energy"

Vze2wgsm1 (talk) 01:17, 14 December 2022 (UTC)

The electrostatic force between alpha and gold is an internal force in the system that we consider here. External forces might come from the gold lattice, for instance, but we've discussed at length why those forces can be neglected here. You might worry, incidentally, about alpha particles that excite gold atoms. In this case, kinetic energy would be lost to internal degrees of freedom and that would have to taken into account. But: these inelastically scattered particles are not measured in the Geiger-Marsden experiment, only the elastically scattered ones are. I also explained why potential energy did not appear in the energy equation that I used. There is no need to consider the dynamic details of the scattering process (aka collisions), we only need to look at the initial and final states. --Wrongfilter (talk) 06:18, 14 December 2022 (UTC)

Thanks Wrongfilter. Forces like gravity and electrostatic are both external and internal. When force causes acceleration, then KE and momentum change. Momentum = mass x velocity. Vze2wgsm1 (talk) 11:08, 14 December 2022 (UTC)

So what? --Wrongfilter (talk) 11:16, 14 December 2022 (UTC)

PianoDan's assumption of conservation of momentum conflicts with acceleration due to electrostatic force.

$m_{\alpha }v_{i}^{2}=m_{g}v_{g}^{2}+m_{\alpha }v_{f}^{2}$

Are you claiming that alpha particle deflection is indeed governed by conservation of momentum? Vze2wgsm1 (talk) 11:40, 14 December 2022 (UTC)

Yes, of course it is. And if you think it isn't then any further discussion is useless. --Wrongfilter (talk) 12:08, 14 December 2022 (UTC)

I accidently put PianoDan's KE equation instead of his momentum equation in my previous post. I should have used the following equation to show that PianoDan indeed assumed conservation of momentum:

$m_{\alpha }v_{i}=m_{g}v_{g}+m_{\alpha }v_{f}$, i.e. $v_{g}=r(v_{i}-v_{f})$

An example that shows momentum is not conserved is:

When the alpha has high velocity, the alpha has high momentum and gold has zero momentum and remains stationary. When the alpha stops while reversing direction, the alpha will have zero momentum and the gold will have zero momentum. Total momentum was initially high, and then became zero.

Note: If you cannot defend your conservation of momentum idea, then my next step is alteration of the Geiger–Marsden experiments article to highlight Rutherford's assumption of zero gold velocity. Vze2wgsm1 (talk) 12:52, 14 December 2022 (UTC)

I wrote down that equation, not PianoDan. And your example is utterly wrong. Any momentum lost by the alpha particle is taken up by the gold nucleus, so that total momentum is conserved. Do not edit the article, any changes you make will be reverted. --Wrongfilter (talk) 13:06, 14 December 2022 (UTC)

Ok, what can I say and what can't I say? Vze2wgsm1 (talk) 13:21, 14 December 2022 (UTC)

If you wish, I can use the talk page. I request participation from uninvolved, interested editors. Vze2wgsm1 (talk) 13:28, 14 December 2022 (UTC)

Your comment: "Any momentum lost by the alpha particle is taken up by the gold nucleus" conflicts with the stated condition that gold nucleus remains stationary. Please explain.

Does your comment: "Do not edit the article, any changes you make will be reverted" indicate that Wikipedia found justification to ban me from making any comments on article? What was the justification? Vze2wgsm1 (talk) 14:17, 14 December 2022 (UTC)

The gold nucleus gains momentum in the same way that a brick wall takes up momentum when you hit it with your fist. Conservation of momentum is not negotiable. However, as has been said before, the resulting speed of the nucleus is small because of its high mass. As an approximation it is therefore justified to neglect that speed and to assume that the nucleus remains stationary. As regards the article: you can of course put in anything that is properly sourced with reliable external references, anything else not. --Wrongfilter (talk) 14:29, 14 December 2022 (UTC)

Any movement of the brick wall conflicts with the (absolutely) stationary gold criteria. If the gold remains stationary, then the KE of the alpha converts entirely into electrostatic potential energy by the time the alpha becomes stationary. Otherwise, the alpha KE would be divided between gold KE and electrostatic potential energy.

I will make sure that any edit I make to a Wikipedia article contains the proper references. Vze2wgsm1 (talk) 15:16, 14 December 2022 (UTC)

You keep missing the point, so I'll try to restate it, as others have, yet again. There is a difference between "doesn't move enough to factor into our calculations, so we'll treat it like it is stationary" and "really-for-real-honest-to-God-didn't-move stationary". As everyone here keeps telling you, when we (and everyone else except you) are saying "stationary", we're referring to the first situation, NOT the second. You keep hearing us tell you the first, and keep arguing against the second, which no one except you is claiming. Yes, the gold nucleus absorbs some of the momentum of the alpha particle. However, it does not absorb enough to make a difference, so we treat it like it's stationary. The mosquito that slams into my car windshield while I am driving down the road also imparts a momentum on my car, but I'd be stupid to spend any effort calculating how much it altered my car's speed. --Jayron32 16:01, 14 December 2022 (UTC)

To provide evidence that a gold nucleus can act like a free particle, I present the following video. The video contains the math for deflection of an alpha particle and a FREE gold nucleus.

https://www.youtube.com/watch?v=5V_1oVbrWLs

Note: I do not claim that deflection from electrostatic repulsion is the same as deflection via a collision. Vze2wgsm1 (talk) 19:47, 14 December 2022 (UTC)

Where in digestion does salt and sugar separate?

Human urine is 95% water, then urea at the next largest, followed by the salt ions of sodium, chloride, and potassium. And so, urine is salty, even if you eat lots of sweet food doesn't make urine more sweet. So that means sugar goes the other route. Sugar is covalent, so covalent foods go the other route, ionic foods go to the urine. Where is that separated? In the liver, blood vessels? Thanks. 67.165.185.178 (talk) 14:19, 11 December 2022 (UTC).

Sugar is metabolized by insulin. The presence of sugar in urine is a symptom of diabetes. Acroterion (talk) 14:22, 11 December 2022 (UTC)

So that happens in the pancreas? And the salt continues to the blood vessels, then to kidneys? 67.165.185.178 (talk) 14:33, 11 December 2022 (UTC).

No, the pancreas supplies the insulin, which is used throughout the body. Read carbohydrate metabolism, digestion, kidney and pancreas. Acroterion (talk) 14:44, 11 December 2022 (UTC)

Okay, so there is selectivity? (Insulin can metabolize sugar without metabolizing salt?) Or, is salt already separated out when the time the insulin meets the sugar? 67.165.185.178 (talk) 14:56, 11 December 2022 (UTC).

Salt is not metabolized, and it is not a source of energy. It is an essential nutrient. See sodium in biology. Acroterion (talk) 17:02, 11 December 2022 (UTC)

Since sugar is covalent, then there must be other things that are covalent like sugar, that insulin also metabolizes that might get in the way? 67.165.185.178 (talk) 17:37, 11 December 2022 (UTC).

Covalence is a property of bonds between atoms, not of compounds such as sugars. The kidney has a filtration system that can separate small ions from larger molecules; see Ultrafiltration (kidney) § Selectivity.  --Lambiam 19:45, 11 December 2022 (UTC)

The glucose is fact filtered into primary urine and then re-absorbed in renal tubules. Ruslik_Zero 20:12, 11 December 2022 (UTC)

I'm looking at Digestion#Carbohydrate_digestion, which states sucrose is broken down by sucrase, and elsewhere it says it happens in the small intestine. Then, carbohydrate_metabolism says insulin and glucagon are the primary hormones involved in maintaining a steady level of glucose in the blood. I also see proteins are being digested in the stomach and small intestines. Now, I'm not seeing anything for salt, so Googling "how does the body digest salt" yields "Sodium is absorbed from the gastrointestinal tract, always bringing water along with it." So something from the intestines can go into the kidneys. And both salt and sugar make it to the small intestines. I'm wondering what is the next place for salt and sugar after the small intestines, directly into the kidneys? And then, kidneys filter out sugar into the renal tubules, salt does not? 67.165.185.178 (talk) 00:53, 12 December 2022 (UTC).

Sugar is a carbohydrate, which is digested. Salt is a mineral/essential nutrient, which is absorbed. One is metabolized, the other is not. There are two distinctly different processes involved,and bio;logically the two substances have drastically different roles and processes. You appear to be proceeding from false assumption of similarity. Acroterion (talk) 01:01, 12 December 2022 (UTC)

But in the small intestines, if you have salt and sugar in water, then the process to suck out salt 1st, from water, then there must be selectivity. Salt ions are smaller than sugar molecules so that should be some amazing selectivity. So it might be the salt are going through pores, like channels. 67.165.185.178 (talk) 02:43, 12 December 2022 (UTC).

Sodium absorption is complex and happens at multiple places along the digestive system. this briefly describes some of them. --Jayron32 12:49, 12 December 2022 (UTC)

Sounds waves vs. light waves.

Can sound waves emit light and can light waves emit sound? Also, note that light-waves is a duality. The particle equivalent of light waves is photons, is there a particle-equivalent of sound waves? Thanks. 67.165.185.178 (talk) 14:46, 11 December 2022 (UTC).

Read Sound wave and Light wave. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:08, 11 December 2022 (UTC)

Read sonoluminescence, acousto-optics and phonon. Also not a good answer, but hopefully a little more to the point. --Wrongfilter (talk) 17:23, 11 December 2022 (UTC)

A 3rd question is are light waves and sound waves actually the same wave, then, can waves emit sound and light at the same time? (And what would you call that.). Unfortunately, those 2 articles don't seem to connect to each other. 67.165.185.178 (talk) 17:52, 11 December 2022 (UTC).

Maybe Bugs' articles are indeed more for you. Now it's unclear to me what you think light and sound waves actually are. --Wrongfilter (talk) 18:03, 11 December 2022 (UTC)

Yes. I never heard people associate sound waves with photons, for example. 67.165.185.178 (talk) 19:24, 11 December 2022 (UTC).

Light waves and sound waves are very definitely not manifestations of a common underlying physical phenomenon. Light waves are waves in the electromagnetic field. Sound waves are waves propagating in a fluid medium consisting of material particles such as molecules. In the vacuum of outer space, there is no sound, but light traverses it without problem. The speed of light is independent of the relative velocity of an observer, which cannot be said for sound waves (see Doppler effect). Even when abstracting from the physical context, these waves have different characteristics. Light waves are strictly transverse, while sound waves usually have a strong longitudinal component. In that respect, stadium waves are more like light waves.  --Lambiam 19:34, 11 December 2022 (UTC)

Tiny correction: Sound waves propagate in all phases of matter, not just the fluid ones. See acoustics. If they didn't, you wouldn't be able to hear them, as at least part of your hearing apparatus in your ear are solid bones (see ossicles).--Jayron32 12:42, 12 December 2022 (UTC)

Walrus's family

If you learned it in high school, it's probably oversimplified, like this diagram

Wikipedia's walrus article says walruses are the only living member of their family, but dictionaries often define a walrus as being "of the seal family". Any 2 biological concepts it is important not to confuse?? Georgia guy (talk) 15:15, 11 December 2022 (UTC)

Our article says

Order: Carnivora

Clade: Pinnipedia

Family: Odobenidae

Genus: Odobenus

Species: O. rosmarus

Pinnipedia include seals too. Dictionaries may be using the term 'family' more loosely. See the cladogram on the Pinniped article for the relationship. AndyTheGrump (talk) 15:31, 11 December 2022 (UTC)

When Illiger introduced the phylonym Pinnipedia, he defined it both as a family and a one-family order.^[2] The taxons of the usual taxonomic hierarchy correspond to cutting up the phylogenetic tree in layers. As far as I can see, there is no clear scientific criterion for where these cuts are made, and cladistics has multiplied the number of reasonable cutting points, obliterating any notion of comparing the cutting point levels in different trees in a sensible ranking system and leading to new taxon names such as suborder and superfamily. The traditional rank names for given clades, such as order, family (not a rank in the original taxonomy of Linnaeus) and genus, are based more on tradition than anything else.  --Lambiam 18:37, 11 December 2022 (UTC)

It's rather arbitrary whether one calls the odobenidae a family and the pinnipedia a clade between order and family, or calls the pinnipedia a family and the odobenidae a clade between family and genus. Declaring a clade with a single species doesn't make a lot of sense, but there could be extinct relatives.

The whole idea of a ranked system made a lot of sense to Carl Linnaeus, who lived a hundred years before Charles Darwin, studied current animals and plants and noted that some were more similar to each other than others, and it still makes a lot of sense to those who study the organisms alive today. From an evolutionary point of view it makes no sense. What at one point in time is a genus of two closely related species may a hundred million years later have evolved into an entire order of hundreds of species. PiusImpavidus (talk) 10:07, 12 December 2022 (UTC)

To reiterate what PiusImpavidus said above in slightly different terms: You are rarely taught all the details of a complex subject in an introductory-level course like one has in high school or early college. Few people make it further into taxonomy than is taught in high school biology, and the classic hierarchy taught in such a class is extremely oversimplified and super-outdated. The modern system of cladistics is much more useful, but also much more nuanced and complex, which is why most people don't learn it. --Jayron32 12:36, 12 December 2022 (UTC)

What is added to wood, to prevent sunlight damage?

As in color change from sunlight. 2 answers I heard of are polyurethane and mineral oil. But, that strikes me as stuff that is easily wiped off, or does it get stuck inside the wood? 67.165.185.178 (talk) 20:50, 11 December 2022 (UTC).

Traditionally in Australia cedar homes are painted with used motor oil. It soaks in. Good thing we don't have bushfires Greglocock (talk) 21:58, 11 December 2022 (UTC)

While there is an article on Photodegradation, there is no section for wood. Search for wood photo-degradation yields results. I personally have used catalyzed polyurethane and added an automotive UV inhibitor (probably HALS) for use on a wooden table; kinda expensive, but that was in the '70s, and it still looks like new. 136.56.52.157 (talk) 23:54, 11 December 2022 (UTC)

Wood preservation article might be helpful. 136.56.52.157 (talk) 00:21, 12 December 2022 (UTC)

There are wood preservation products, some use something called Trans-Oxide® which the manufacturer claims are manufactured to have needle-shaped particles that will not scatter light even when fully dispersed in the coating or vehicle. This makes them completely transparent and yet still able to impart high color tint strength, weather resistance and UV-barrier properties.^[3] Exterior Danish Oil UV^[[4] includes UV inhibitor compounds [...that] absorb harmful ultraviolet light wavelengths and emit them harmlessly in the infrared range as heat. They don't say what the "compounds" are, but probably includes metallic oxides. 136.56.52.157 (talk) 01:08, 12 December 2022 (UTC)

For not-too-expensive general use see: tung oil. 136.56.52.157 (talk) 01:17, 12 December 2022 (UTC)

I immediately thought of creosote which is cheap and widely used on wood in fences and other outdoor settings. Mike Turnbull (talk) 11:59, 12 December 2022 (UTC)

FYI: Creosote is banned in many jurisdictions, you'll have to put up with substitutes like CreoCote™. They claim to be as good as the original. Martin of Sheffield (talk) 15:41, 12 December 2022 (UTC)

• Keeping wood from changing colors is often done via the use of wood sealants. The main options for wood are varnish and lacquer. Generally three things can degrade the color of wood; being water, oxidation (air), and light. Good sealants will stop water and air from fading the wood; and some will have materials that absorb UV light, which will additionally block most of the oxidative effects of sun. --Jayron32 14:20, 12 December 2022 (UTC)

Enteroctopus date: 1887 or 1889?

Most sources state the genus Enteroctopus was created by Alphonse Tremeau de Rochebrune and Jules François Mabille in 1889; however this is not entirely correct; It was published in 1889 in Mission scientifique du cap Horn, 1882-1883 but the very same book affirms it was created two years before, in 1887. So, what is the correct date? -- Carnby (talk) 21:25, 11 December 2022 (UTC)

Wasn't the genus created on the Fifth day of Creation? :) Generally, one goes by the publication date.  --Lambiam 01:27, 12 December 2022 (UTC)

The 1889 article indeed gives the taxonomic authority of the binomial name Enteroctopus megalocyathus as Rochebrune & Mabille 1887. As a confusing side issue, nowadays we would write "Enteroctopus megalocyathus (Gould, 1852)" because Gould had come up with the species name already, but Rochebrune & Mabille here coined the generic name and they wrote themselves as the authors of the combination of the two names (a bit like the rules botanists still follow). The 1887 date is erroneous. It seems that their intention was to indicate that this name was new in their current work, and that they were both authors of this description. Presumably they expected their manuscript to be published in 1887, but in fact it appeared in 1897 1889 and nobody changed the date in the meantime. It is the actual date of publication that now counts. https://doi.org/10.11646/zootaxa.2723.1.2 probably explains more but is behind a paywall. Jmchutchinson (talk) 23:42, 13 December 2022 (UTC)

December 12

Fluorine (and neon) 2s shell

Resolved

Normally, we talk about fluorine as having 2s and 2p as valence orbitals, for seven valence electrons. However, there's a huge difference in orbital energies between these two, and actually fluorine 2s has a lower energy than the core 5p orbitals in the lanthanides. So, how significant is the contribution of fluorine's 2s shell to chemical bonding? And what about neon? Double sharp (talk) 08:10, 12 December 2022 (UTC)

The matter has apparently been discussed on Chemistry Stack Exchange. Some MO diagrams for SF₆ and HF are given to support fluorine 2s as inactive. But that doesn't prove that fluorine 2s is always inactive, only that it is in those compounds. Looking at orbital energies throughout the periodic table, I'd expect it to be more possible in something like BrF+6 and indeed this paper finds some fluorine 2s bonding contribution there.

So I suppose I managed to track down an answer for my original question and the natural follow-up has become "OK, so what are the valence orbitals of neon"? Double sharp (talk) 09:03, 12 December 2022 (UTC)

Well, this distinguishes 2p vs 2s in solid neon as the outer vs inner valence regions. I guess this gives the answer to "what are the valence orbitals of neon" in a natural context when that question is meaningful. Double sharp (talk) 09:51, 12 December 2022 (UTC)

uploading unpublished government technical reports

I would like to know if documents pertaining to a Wikipedia page can be uploaded as pdf files. These are government technical reports which have not been formally released for various reasons. Rdhara (talk) 21:49, 12 December 2022 (UTC)

The Help desk is better prepared for this type of question. 136.56.52.157 (talk) 23:51, 12 December 2022 (UTC)

December 13

Starting the engine of military vehicles

Random thing that someone was wondering about in the bar tonight. Do tanks, fighter planes and attack helicopters have a set of keys for the doors and the ignition? — Preceding unsigned comment added by 146.200.126.234 (talk) 00:04, 13 December 2022 (UTC)

I don't have a general authoritive answer, but keys have long been used in private ownership vehicles because of theft. Industrial vehicles such as bulldozers have traditionally needed no key for starting, as practically nobody wanted to steal them.

My father bought a World War 2 surplus British made tank. There was no key - anybody could enter and start it. It had an aircraft-style ignition lever switch - off/one/two/both (the engine had 2 spark plugs per cylinder- you are supposed to test running on one set of plugs at a time, to prove both work) and a push-button to crank it.

Last year, a former iron curtain country had some sort of celebration in which their state museum supplied a restored Russian made tank (T54 or similar). Leaving it on public display, they took the battery out, thinking this would immobilise it. A couple of old guys, probably a somewhat drunk, showed up and they had served years before in the same sort of tank. They knew it had an emergency air start system in case of a dead battery. So they started the tank using the air system and drove off with it.

Our army sold of a few old Armoured Personnel Carriers (APC). I inspected one (M113 or similar) at the dealer's yard. They invited me to start it - it needed no key. It had a simple lever on/off switch for electrical power, and a push-button to activate the starter motor.

There are a number of military aircraft start procedure videos on YouTube. There's no key.

One can imagine a scenario: "We are under overwhelming fire. Quick, corporal, start the truck and let's get out of here!" "Uh, sorry Sarge, I dropped the keys in the mud. Can't find them now." Dionne Court (talk) 00:54, 13 December 2022 (UTC)

This article in ARMY Magazine, criticising the US Commercial Utility Cargo Vehicle or M880 (a military pick-up truck), cites the provision of a common ignition key as a disadvantage; "Imagine trying to bug out and having to fumble for a key to start the truck". Alansplodge (talk) 22:21, 13 December 2022 (UTC)

Examples Where Genetics was used to determine definitions of genus and species

I recall that there were examples where the definition of a species, genus, etc. were redefined based on genetic analysis. E.g., we thought that Chimp was a species but we changed it to be a genus or we thought a Sea Horse was a fish but we changed it to an Anthropod (I'm making that last one up but I think the first one might be true). I can't remember where I read this though and I've looked through Wikipedia and my books and can't find anything. Would appreciate any examples and refs. MadScientistX11 (talk) 00:59, 13 December 2022 (UTC)

Here are some examples; there are probably countless more.

• The Arctic warbler was formerly thought to include various populations that breed in Asia, but these are all now considered distinct species.
• The black Sumatran langur was formerly considered a subspecies of the brown long-eared bat, but is now treated as a separate species.
• The black-and-white langur was formerly considered a subspecies of the black-crested Sumatran langur, but is now treated as a separate species.
• The Calabria pine vole was formerly considered a subspecies of Savi's pine vole, but is now treated as a separate species.
• The East Sumatran banded langur was formerly considered a subspecies of the Raffles' banded langur, but is now treated as a separate species.
• The European green toad was formerly thought to include various mainly Asian populations, but these are now considered distinct species; together they have been assigned a new genus, Bufotes.
• Imaizumi's red-backed vole was formerly considered a subspecies of the Japanese red-backed vole, but is now provisionally treated as a separate species.
• The Japanese long-eared bat was formerly considered a subspecies of the Sumatran surili, but is now treated as a separate species.
• The Siberut langur was formerly considered a subspecies of the Mentawai langur, but is now treated as a separate species.

 --Lambiam 07:56, 13 December 2022 (UTC)

For an example regarding some species of gulls, see Larus#Ring species. Long story short – we thought they were a Ring species, but a recent genetic study (linked as a reference) has shown that it's even more complicated than that. {The poster formerly known as 87.81.230.195} 90.213.188.15 (talk) 14:21, 13 December 2022 (UTC)

Metallising fluorine

Resolved

Has anyone ever measured the pressure necessary to form an expected high-pressure metallic phase of F₂? Or calculated what it theoretically ought to be? Double sharp (talk) 03:07, 13 December 2022 (UTC)

According to this 2020 paper, it apparently has never been experimentally found (well, no surprise given that it seems like a safety nightmare), but that doesn't exclude it having been calculated. Double sharp (talk) 04:14, 13 December 2022 (UTC)

Per this 2020 paper there have been experiments (with inconclusive results) and the theoretical metallisation pressure for fluorine is 2500 GPa (with a novel tetragonal P4₂/mmc structure). So I've once again answered my own question. Double sharp (talk) 04:18, 13 December 2022 (UTC)

Updated metallization pressure (and also the French article). Don't think anyone has calculated it for radon. Double sharp (talk) 04:35, 13 December 2022 (UTC)

Scientific articles about beef versus Impossible Burger that are not commissioned by the latter?

I've been seeing a lot of the 89% statistic about "global warming potential" from the life cycle analysis that Impossible Foods commissioned from Quantis. This number seems to be repeated commonly, and so I was looking for other studies/scientific articles about the same topic that were not commissioned by Impossible Foods so I could further evaluate the claim. 777burger ^{user talk contribs} 03:49, 13 December 2022 (UTC)

Producing an adequate life-cycle assessment of a product in conformance with the ISO 14040 and 14044 framework and guidelines is a substantive effort of a type that does not help one to earn scientific brownie points. Such a study is unlikely to be undertaken by a scientific establishment unless specifically commissioned. Prior to publication, the LCA was reviewed by an independent panel of academic experts, who found no major issues. In particular, it found that that the methods used are scientifically and technically valid. The report produced by Quantis can be downloaded from the Web,^[5] and is detailed enough that anyone who is interested can check that data from other studies have been properly cited and reproduced and can check the computations. It would be interesting to make a comparison with other "fake meat" products, but I bet that for most one would find very similar results. The report can be read more as an indictment of run-away meat production than as an ad for specifically Impossible Foods. One might even say that beef is the more impossible food.  --Lambiam 07:26, 13 December 2022 (UTC)

What is thirtylone?

Transferred from Computing desk

i wanna do some research about What is thirtylone?if you have the idea about you can help me in my research Elsiewright343 (talk) 13:44, 13 December 2022 (UTC) — Preceding unsigned comment added by 95.145.0.90 (talk)

As far as I can tell, it's whatever anyone wants it to be. There doesn't seem to be any single real chemical compound with that name, and nothing recognized as such with a CAS number. It seems to usually be used for various forms of amphetamines or analogs of MDMA, but basically as a name it gets used by the illicit designer drug community for whatever new compound they come up with in these families as existing compounds get banned. Don't buy it, don't do research on using it, as you have literally no idea what you are getting. You don't know what compound they are even promising, let alone whether it is actually containing that compound, in what purity, what else it is mixed with, and I guarantee zero research or testing on safety. --OuroborosCobra (talk) 15:52, 13 December 2022 (UTC)

@Elsiewright343 It is here on Chemspider and here on wikipedia. I wouldn't touch it with the proverbial barge-pole. Mike Turnbull (talk) 16:18, 13 December 2022 (UTC)

Help

What was the most recent common ancestor of dinosaurs and mammals? Allaoii ^talk 19:31, 13 December 2022 (UTC)

It would have been whatever animal existed when Sauropsids (reptiles, dinosaurs, and birds) and Synapsids (mammals and their reptile-like ancestors) diverged, probably living sometime in the Pennsylvanian, likely earlier than 306 million years ago, when the oldest known synapsid evolved. --Jayron32 19:39, 13 December 2022 (UTC)

You are looking for a basal amniote. -- Verbarson  ^talk_edits 19:43, 13 December 2022 (UTC)

i remember reading something that named a specific creature, im trying to find its name Allaoii ^talk 20:01, 13 December 2022 (UTC)

I'm not sure we know it down to that level of precision. The vast majority of species have been unidentified. It seems unlikely in the extreme that the specific species that was the MRCA is known. --Jayron32 21:11, 13 December 2022 (UTC)

well it was star trek... Allaoii ^talk 21:27, 13 December 2022 (UTC)

Ah, the Voyager episode "Distant Origin." It claimed that MRCA to be eryops, which is probably not correct, since it is an amphibian that lived after the first reptiles evolved, and so isn't an ancestor of either dinosaurs or us. Also, the organism they pictured in the episode is not an eryops at all. According to Memory Alpha, the pictured animal is likely a gorgonops, which is already a mammal like reptile. It might be among our ancestors, as a stem group leading to all mammals, but that would already put it after the split between sauropsids and synapsids. So, yeah, Star Trek got this wrong in a lot of ways. --OuroborosCobra (talk) 21:35, 13 December 2022 (UTC)

...wanna be nerd friends? Allaoii ^talk 21:37, 13 December 2022 (UTC)

that reminds me, is the "most evolved dinosaur" they showed real, and if so, what is it? Allaoii ^talk 20:38, 14 December 2022 (UTC)

Try this. Alansplodge (talk) 22:39, 13 December 2022 (UTC)

read the other replies before commenting Allaoii ^talk 22:51, 13 December 2022 (UTC)

Yes. I was providing a reference, this being a reference desk. Alansplodge (talk) 15:07, 14 December 2022 (UTC)

one of the other replies already answered my question. Allaoii ^talk 17:17, 14 December 2022 (UTC)

This is the reference desk, not the answer desk. Alansplodge did exactly what they were supposed to. --Jayron32 19:52, 14 December 2022 (UTC)

December 14

Gamma decay.

So the shortest wavelength in the EM spectrum are gamma rays, then x-rays. It appears to me that gamma rays are called gamma rays because they have only been gamma rays emitted. If they can emit wavelength in the x-ray range, then they can get a name change. Have scientists been working on finding gamma decays to emit in the x-ray range? Also, if I look at gamma decay, and sort the shortest gamma ray, to the longest gamma ray, what is the pattern, from the decaying point of view? Nucleus mass? Do scientists predict they can 1 day have decay emit x-rays? And maybe win a Nobel prize if someone discovered a way. 67.165.185.178 (talk) 01:25, 14 December 2022 (UTC).

The total energy released in radioactive decay is the energy equivalent of the difference in mass (by $E=mc^{2}$) between the parent nuclide and daugher nuclide(s). The energy of a photon is given by the Planck relation, $E=hf={\frac {hc}{\lambda }}$, which implies that longer gamma rays carry less energy and shorter gamma rays carry more energy. Indeed, very low energy decays can produce x-rays or even ultraviolet rays in the case of the remarkably low-energy nuclear isomer thorium-229m (Sources: [6] [7]). ^Complex/_Rational 01:56, 14 December 2022 (UTC)

Excellent. And all these gamma rays, are ionizing. Can this thorium-229 or so, release the radiation that are non-ionizing? 67.165.185.178 (talk) 03:42, 14 December 2022 (UTC).

The excitation energy of Th-229m is less than 10 eV, which is commonly used as a threshold for ionising radiation. So, yes, it would emit non-ionising radiation by this definition. Though usually the gamma vs X-ray (or in this case UV!) distinction is by origin rather than wavelength. Double sharp (talk) 03:47, 14 December 2022 (UTC)

Double sharp's last sentence is important. An alternate and fairly common distinction between the two types of radiation is for "X-rays" to be the result of electronic reactions vs "gamma rays" coming from nuclear reactions, rather than a bright-line (ha!) delineation of wavelengths. X-ray#Energy ranges has a discussion. DMacks (talk) 03:58, 14 December 2022 (UTC)

It depends on whom you ask. The people who generate their own radiation (like radiologists) discriminate between X-rays and gamma rays by source, i.e., the apparatus they need to generate it. The people who only observe the radiation (like astrophysicists) discriminate only on energy, putting the threshold at something like 100 keV. PiusImpavidus (talk) 09:54, 14 December 2022 (UTC)

Yeah, I'm used to the nuclear-physics convention that anything coming out of a nucleus is gamma (even if by wavelength it's UV in the case of Th-229m), but indeed definitions vary between fields. Double sharp (talk) 14:54, 14 December 2022 (UTC)

Oh, and what does the m symbolize, in thorium-229m? 67.165.185.178 (talk) 04:01, 14 December 2022 (UTC).

What did you learn when you clicked on the thorium-229m link? DMacks (talk) 04:03, 14 December 2022 (UTC)

Oh okay, it stands for metastable. 67.165.185.178 (talk) 04:08, 14 December 2022 (UTC).

I want to underline something that several commenters here have said from different points of view:

Gamma rays and X-rays are the same thing. They're both just photons. Classifying photons by wavelength, energy, or source can be very useful for a number of reasons, but it's important to remember that these are still just sub-categories (with somewhat conflicting definitions) of the same fundamental thing. PianoDan (talk) 16:45, 14 December 2022 (UTC)

Just to really drive home the point that PianoDan is making above, the different "kinds" of electromagnetic radiation (gamma rays, X-rays, UV, light, IR, microwaves, radio waves) are all the same thing. There is no difference between any of them on a fundamental level except the wavelength, but in every other way, they are exactly the same phenomenon. When we use words like "gamma rays" or "X-rays" or "visible light" to describe certain ranges of wavelengths, we're largely doing so to make it convenient for us to explain how we use those forms of EM radiation, and in some cases are really just historical artifacts to a time when we didn't understand this stuff as well as we do now. When we named, for example, X-rays and gamma rays, we didn't really know what they were. X-rays have that "X" at the front because because Wilhelm Conrad Röntgen, when he first described them, didn't know what they were, so he used the standard placeholder "X" meaning "unknown" for the name, and it kinda just stuck. When gamma radiation was named, it was named because it was the third time of nuclear radiation (which is to say, radiation given off during nuclear decay discovered. No one really knew what it was, but since alpha radiation (the first so discovered) and beta radiation (the second so discovered) already had names, Paul Ulrich Villard, who discovered this third type, just kept the pattern going. Notice, however, that none of these names has anything to do with what the radiation actually was. It turned out that X-rays and gamma radiation were basically the exact same thing, so for mostly historical reasons, we differentiate the name by the process that produces it, rather than by any fundamental difference in the particles themselves. You see the same thing all the time; for example alpha particles are just helium 4, beta particles are just electrons. It's certainly no different than you calling your mother "Mom", but her brother calling her "Susan" or whatever. Different names in different contexts don't mean they are different things. The same thing can have multiple names. --Jayron32 18:11, 14 December 2022 (UTC)

Collisions at railroad crossings

Statistically, does California experience a disproportionately high number of collisions between trains and pedestrians and/or road vehicles at level crossings (when compared to other states)? If so, does the number remain disproportionate if corrected for the main confounding factors (namely, (1) the amount of population living in communities with active railroad tracks running through them, (2) the number of trains operating daily within the state and (3) the number of ungated railroad crossings and/or the mileage of street running)? If so, what are the possible reasons why the number is so high? (Because it certainly seems that way -- a person I know who rides Caltrain regularly told me that he experienced delays almost every week on average (!!!) due to either his train or another train ahead of him hitting someone or something on the tracks, and when I rode the Coast Starlight up to Salem a couple months ago, I experienced these delays personally -- the northbound train pulled into San Jose a full 4 hours late due to having run over some stupid hobo in Salinas, whereas the southbound train got to Salem exactly on time and kept going as far as Oakland without delay, but between Emeryville and Jack London Square we had an emergency stop due to some idiot driver pulling onto the tracks right in front of the train without looking (fortunately we were going dead-slow and therefore didn't collide, so we were only delayed 10 minutes or so). So, is California really that bad in terms of collisions at railroad crossings, and if so, why might that be? 2601:646:8A81:6070:8D7A:87F9:2C1B:94A0 (talk) 08:03, 14 December 2022 (UTC)

According to Operation Lifesaver which exists to prevent these types of collisions, Texas is #1 in the number of collisions and California is #1 in deaths caused by such collisions. This is not surprising since those are the two most populous states with California being most populous. The death rate in California per 100,000 residents is close to the national average. This is a nationwide problem although 234 deaths a year in a country of 332 million people is not a major cause of death. Pancreatic cancer, for example, kills about 50,000 Americans each year. As a long term resident of the Bay Area, I am well aware that Caltrain has a bad reputation for this type of disaster, since it is a heavily used commuter rail line between San Francisco and San Jose, with plenty of grade crossings and ample opportunities for pedestrians to engage in dangerous behavior. This article from 2000 reports 90 deaths in the previous eight years, which would be less than one a month but would certainly have an impact on daily commuting. Many of those deaths were suicides. Talking about "stupid hoboes" is pretty much guaranteed not to be useful. There are obvious safety improvements that should be made, such as eliminating grade crossings, but that would cost many billions of dollars and take decades. That is part of the California High-Speed Rail program, which is behind schedule and over budget. Cullen328 (talk) 10:17, 14 December 2022 (UTC)

For comparison, 5 people were killed at UK level crossings in 2020/21, [8] 2 in 2019/20 and 2 in 2018/19. [9] The population of the UK is 67 million, nearly double that of California, with a much denser rail network. Alansplodge (talk) 15:04, 14 December 2022 (UTC)

But California has over 10,000 level crossings, almost twice as many as the UK. To compare them properly you'd need to analyze both places in terms of the number of road vehicles and the number of trains that use the crossings daily. I'm not searching, but I doubt that those statistics will be easily found. --174.89.144.126 (talk) 15:32, 14 December 2022 (UTC)

wormholes

hello i would like to ask if resonant tunneling antenna diodes can generate wormholes. thanks very much. 2607:FEA8:BCE0:D500:75E8:5E73:E7C8:DE4 (talk) 15:38, 14 December 2022 (UTC)

No. --Wrongfilter (talk) 15:44, 14 December 2022 (UTC)

More specifically, quantum tunnelling and wormholes are not the same thing. --OuroborosCobra (talk) 16:02, 14 December 2022 (UTC)

from internet searches i found macroscopic and electromagnetic quantum tunneling can generate wormholes. is that this correct. 2607:FEA8:BCE0:D500:D9DA:4F2F:3CE:E4B6 (talk) 17:42, 14 December 2022 (UTC)

Please read the Wikipedia articles you have been sent to read. Wormholes and quantum tunnelling are entirely unrelated phenomena, and have nothing to do with each other. Wormholes are a consequence of gravity, and are thus explained by general relativity. Quantum tunnelling, as the name implies, is a result of quantum mechanics. It is not an electromagnetic effect, per se, but rather due to the way that all elementary particles behave. The quantum tunnelling article actually has a nice, lay-person level explanation in the "Introduction to the concept" section.--Jayron32 17:59, 14 December 2022 (UTC)

Water's boiling point

One of the things that allow life to exist on Earth is that liquid water is available in large numbers. This is because of the distance to the sun, but also because of our atmosphere and its pressure, that allow a wide temperature range for liquid water (from 0º to 100º). If Earth was in the same orbit but had a lower atmospheric pressure, that range would be way more limited. And IIRC, with no atmosphere water would sublimate from ice to vapor directly.

This is something I simply know, but I would need a proper source for it. I'm listing in a sandbox all the reasons that allow life to exist on Earth, from an astronomical perspective, but all the sources I find that explain our liquid water attribute it only to the goldilocks zone, making no mention to the atmospheric pressure. Cambalachero (talk) 19:06, 14 December 2022 (UTC)

What you're looking for is a phase diagram of water, or even more simply the triple point of water. The pressure at the triple point is the lowest pressure at which a liquid could exist, so any pressure less than about 0.006 atm (0.6% of the earth's atmospheric pressure) would not be able to support liquid water. The relationship between pressure and boiling point is seen on any phase diagram as the liquid-solid line on the graph. If you want a text description, it's really basic stuff taught in any first-year chemistry class. Here it is in LibreText Chemistry and Here it is on OpenStax Chemistry, for two free entry-level chemistry textbooks. I can't imagine that literally every entry-level chemistry text book doesn't discuss the relationship between pressure and phase changes. It's REALLY basic stuff. --Jayron32 19:49, 14 December 2022 (UTC)

If the motivation here is to explore limits of alternative "Goldilocks zones," we might need to freeze the discussion (sorry, bad pun) and revisit exactly what that zone is.

If we're reducing it to a few words of sound-bite, we might say that a planet is in the Zone if liquid water exists on that planet.

But hang on - we also want to say, "... and we're looking for liquid water because... ... it's an important part of every form of plausible biochemistry that we're interested in - even the plausible alternative xenobiology that borders on the speculative!

At the same time, the so-called "habitable zone" also has other requirements. If the liquid water is in equilibrium at an ambient temperature that is so hot that it's denaturing proteins, then protein-based biology won't work: that's "not the habitable zone." If it's so cold that metabolism is chemically unsustainable, that's also "not the habitable zone." We can imagine biochemistries that are very different from our fundamental earth-like biochemistries - and we can even test some of this in a lab - but there are still limits! And so we can traverse down the speculative, alternative, plausible sorts of "habitable" zones for speculative, alternative, plausible sorts of non-Earth-like life forms, ... just bear in mind that as you stray farther afield, even the requirement for liquid water will also evaporate (sorry, bad pun).

Here's a NASA website that talks about the Kepler Occurrence Rate, and here's the SETI study that goes into the boring details; and if I may editorialize a bit - NASA had to make some "clarifying editorial updates" to their press release in order to keep things more science-y and less fiction-y.

Real scientists do care about this stuff, but they have to mince words, define terms, and tread very carefully. Speculation is fine as long as we are still making meaningful scientific statements - which fundamentally boils (sorry) down to falsifiability and testability.

Nimur (talk) 21:12, 14 December 2022 (UTC)