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October 1

Spark in a flame.

My gas operated refrigerator (in my caravan) has a battery-powered igniter, and the sparking tip of it is about 6mm above where the gas and air mixture comes out of the mixing tube. To light the gas I switch on the igniter, and it sparks away until the gas mixture ignites, then it stops sparking even though the switch is still turned on. There is no heat-detecting mechanism to turn it off, so why does it stop? I am assuming that when there is a flame surrounding the igniter tip it acts as an insulator, but I have no idea why this would be so. Can someone explain what is happening please??49.197.133.215 (talk) 04:55, 1 October 2021 (UTC)

The flame is actually probably (very slightly) more conductive than the cold gas. I therefore suspect that the terminal of the spark plug contains an inbuilt heat detector. A voltmeter should be able to tell if the igniter has been disengaged, but may be hard to apply near the flame. Is it possible to keep the igniter turned on after the gas is turned off? If so, does it begin to spark again very quickly, or only after a considerable delay?  --Lambiam 05:33, 1 October 2021 (UTC)

(OP) It starts to spark again as soon as the gas flow ceases.49.197.133.215 (talk) 07:40, 2 October 2021 (UTC)

• It depends which flame and where in the flame exactly, but a flame is a plasma, meaning a soup of ions and electrons, meaning it is very conductive (much more than air). See for instance this article about the conductivity of an oxyfuel cutting torch.

OP’s gas igniter probably a spark generator circuit. It generates a high voltage to charge a capacitor in parallel with the air gap; when the capacitor starts charging the air gap is an insulator, but when you reach the breakdown voltage of the air gap then you have a (conductive) spark that discharges the capacitor; once the capacitor is discharged, the air becomes an insulator again and the cycle starts anew. See [1] for an electrical scheme (although I am not sure a transformer is used in small sparkers). When the air gap is flooded with a conductive flame, the capacitor cannot charge because the gap is conductive. Tigraan^{Click here for my talk page ("private" contact)} 15:30, 1 October 2021 (UTC)

Strictly speaking, only the fire zone of the flame, a thin boundary where the chemical reaction takes place, is plasma. The reaction product is not hot enough to remain a plasma for more than a fleering instant, and you would not be able to use the flame as a welding torch.  --Lambiam 21:55, 3 October 2021 (UTC)

(OP) Thanks, that sounds like the likely explanation. Wouldn't that mean it is still using up the battery power all the time the fridge is on? There is no mention in the operating instructions to turn the igniter off until you turn the gas off!!49.197.133.215 (talk) 07:40, 2 October 2021 (UTC)

It probably uses some electricity, but not much. I searched for actual numbers, but I did not find them, either by using "electric lighter" or "spark plug" as keywords (in addition to "voltage", "intensity", etc.).

I tried guessing, but it did not really work out: from the oxyfuel study linked above (fig 15) the flame resistance is at least R=20kΩ, and from Paschen's_law#Long_gaps and reasonable guesses on the design (about 1mm gap, voltage not much higher than needed to spark) we can guess the sparker voltage is about 4kV, but this gives a power across the gap of P=U^2/R=800W. That is about as much as a microwave, so, unrealistically high. Most likely, the circuit upstream of the gap produces 4kV voltage only when no current goes through, and it drops sharply as soon as some a few mA go through, so that taking 4kV as a steady-state value for conduction through the flame is incorrect. Tigraan^{Click here for my talk page ("private" contact)} 16:10, 3 October 2021 (UTC)

(OP) Thanks Tigraan 49.197.60.127 (talk) 00:49, 6 October 2021 (UTC)

Skybridge apartments

Has anyone built a tall building where some (more than a few) or all apartments are cantilever bridges? Sagittarian Milky Way (talk) 14:47, 1 October 2021 (UTC)

How would that work? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:02, 1 October 2021 (UTC)

What do you mean? You could have 2 or more towers (which could be anything from a typical residential tower to an apartmentless vertical concrete bunker probably hidden with thin shells (i.e. fake tinted glass wall, marble over concrete in the elevator area)) with a c. 1 room-wide apartment connecting them on every other floor. Engineeringly I think it could be done, don't know about economically. Might take some weird local things like zoning based on floor:land ratio but not height and high need for wind resistance. Sagittarian Milky Way (talk) 16:29, 1 October 2021 (UTC)

How about The Interlace? --Amble (talk) 20:22, 1 October 2021 (UTC)

Not the way I was thinking but a very aesthetic way to do it nonetheless. At ~200x300 yards it couldn't fit on 2 Manhattan blocks glued together! Sagittarian Milky Way (talk) 03:47, 2 October 2021 (UTC)

Maybe OMA was inspired by the "stacks"^[2] of Ready Player One. :)  --Lambiam 08:39, 2 October 2021 (UTC)

Why do Step up transformer used in transmission lines if it decreases the current ?

I just discover Step-Up transformer has more windings in secondary coil than primary coil.

I also discovered that this transformer will decrease current output. If it decrease the output, then why do we use this transformer in transmission lines? Rizosome (talk) 15:27, 1 October 2021 (UTC)

It is all explained at Electric power transmission. Basically, transmitting at high voltages reduces resistive losses. Mike Turnbull (talk) 15:34, 1 October 2021 (UTC)

What did you "discover" when you used a step down transformer? What happened to the current then? --OuroborosCobra (talk) 17:34, 1 October 2021 (UTC)

"Current output" is irrelevant. What counts is power, which is given by the product of current and voltage.  --Lambiam 20:19, 1 October 2021 (UTC)

Sugar in textured vegetable protein

A cup of soybeans contains 300 kilocalories, 31 g protein, 15 g fat, and 5 g sugar. A cup of textured vegetable protein (usually made from soy) contains 300 kilocalories, 48 g protein, 1 g fat and 16 g sugar. I understand that TVP is made from defatted soy flour, which explains the reduction in fat. But what explains the higher sugar content in TVP? Where does it come from? Lantzy : Lantzy 21:17, 1 October 2021 (UTC)

Most processed foods use added sugar in the form of high-fructose corn syrup. I haven't found a specific reference to that use for TVP but if you look at the list of the ingredients on the packet in the supermarket you should see it: possibly called HFCS 42. The idea is that the consumer still needs energy from their food, not just protein, so the carbohydrate provides that. Mike Turnbull (talk) 10:51, 2 October 2021 (UTC)

If you remove a composite part out of something, then, for any measured amount of what remains, the surviving parts should form a greater percentage of the whole than previously. I doubt that manufacturers ever add sugar to provide energy (except in energy drinks etc.) - usually it's added to make something more palatable and/or cheaper to manufacture. Our article on TVP doesn't indicate if there are any ingredients other than de-fatted soya, but it can be surprising what goes into the manufacture of processed foods such as this (for instance, jackfruit, which apparently has a meat-like texture, is used to make a vegan imitation of pulled pork - as described in this BBC article). PaleCloudedWhite (talk) 13:30, 2 October 2021 (UTC)

I think there may be an alternative explanation that partly or completely accounts for the difference. I don't know where the OP's figures come from but we have "Soybean, mature seeds, raw" and "Textured vegetable protein, dry" in our articles per 100g and from the USDA as is the norm with our figures. They are a little different, but maybe not so different.

Raw soybeans have 19.9g fat, 36.5g protein, 8.5g water and 30.2g carbohydrate made up 7.3g sugars and 9.3g dietary fibre. The TVP is 1.2g fat, 51.5g protein, 7.3g water and 33.9g carbohydrate made up of 16.4g sugars and 17.5g dietary fibre. Some obvious things stick out here. The relative proportion of protein has increased more (around 41% increase) than carbohydrate (around 12% increase). However dietary fibre and sugars have increased even more than protein, 88% for the dietary fibre and 125% for the sugars. They now represent basically the entirety of the carbohydrate content, unlike before where there was about 13.6g of other carbohydrates a greater proportion that anything else. According to Soybean#Carbohydrates:

The principal soluble carbohydrates of mature soybeans are the disaccharide sucrose (range 2.5–8.2%), the trisaccharide raffinose (0.1–1.0%) composed of one sucrose molecule connected to one molecule of galactose, and the tetrasaccharide stachyose (1.4 to 4.1%) composed of one sucrose connected to two molecules of galactose.[citation needed] While the oligosaccharides raffinose and stachyose protect the viability of the soybean seed from desiccation (see above section on physical characteristics) they are not digestible sugars, so contribute to flatulence and abdominal discomfort in humans and other monogastric animals, comparable to the disaccharide trehalose. Undigested oligosaccharides are broken down in the intestine by native microbes, producing gases such as carbon dioxide, hydrogen, and methane.
Since soluble soy carbohydrates are found in the whey and are broken down during fermentation, soy concentrate, soy protein isolates, tofu, soy sauce, and sprouted soybeans are without flatus activity. On the other hand, there may be some beneficial effects to ingesting oligosaccharides such as raffinose and stachyose, namely, encouraging indigenous bifidobacteria in the colon against putrefactive bacteria.

I couldn't find the definition of sugars used by the USDA, but I'm guessing it excludes undigestible oligosaccharides which is also supported by the unspecified type of carbohydrate in the sugars. Going by our article, it seems unlikely much of it is starch or similar. (To avoid confusion, the remaining unspecified content in the soybean is mostly "ash" [3], see the USDA data [4].)

Despite the possible advantages of consumption, the negative effects of the oligosaccharides are likely too undesirable. So even if the processing of the defatting process doesn't hydrolise them to at most disaccharides and probably monosaccharides, I'm not surprised it's an additional step. Whatever starch is present is I guess also hydrolised.

The reason for the higher dietary fibre yet lower relative proportion of carbohydrate, that I'm less sure of. It might be a combination of what is lost and kept during processing, the source of TVP not being the same as soybean, mature seeds, raw; and especially the intersection of that with variation between samples.

Nil Einne (talk) 07:51, 3 October 2021 (UTC)

I found [5] which supports my earlier hypothesis based on what our article said that the amount of starch is low in soybeans at the stage they are commercially harvest for oil. Nil Einne (talk) 11:37, 3 October 2021 (UTC)

October 2

Volumes of non-ideal solutions and thermodynamic activity

How can densities data of non-ideal solutions at various temperatures (and perhaps even various pressures) be used to determine the thermodynamic activity coefficients, considering the relations involving partial derivatives of the activity coefficients like

${\bar {V}}_{i}^{\mathsf {E}}=RT{\frac {\partial }{\partial P}}\ln(\gamma _{i})$ (excess partial molar volumes)

obtained from the relation of the activity coefficient to the excess partial molar Gibbs energy

${\bar {G}}_{i}^{\mathsf {E}}=RT\ln \gamma _{i}$?--178.138.98.154 (talk) 00:59, 2 October 2021 (UTC)

Wow no responses yet? I'd ask at Reddit ChemPros and Chemistry StackExchange. The 2nd has lots of PhD candidates there. 67.165.185.178 (talk) 02:48, 6 October 2021 (UTC).

Washed out colors in videos on Ryzen 7 5700U

I bought a Lenovo Flex 5 15.6" 2-in-1. Nice images. I was starting to enthuse about the machine, even if it's a bit large, although large has its own benefits, but then I went to utube. Videos looked distractingly washed out in places, in what I assume to be the motion blur that some reviews complain about on a similarly-specced Yoga model. Given the same manufacturer, I assume the problem has the same cause.

I find it hard to believe that in 2021, spending over $700 on a laptop, I would have trouble watching the simplest videos. Is this normal? What's causing it? Thank you. Imagine Reason (talk) 03:22, 2 October 2021 (UTC)

I'm not sure what Yoga problem you're referring to as you provided no links but motion blur or ghosting does not sound like the same problem as washed out colours to me. Both could be because of a poor or defective panel but again in different areas. Especially for video playback it's also unlikely either have anything to do with the GPU or CPU or really any other parts of the hardware i.e. the only thing that likely matters is the panel not how well specced the other hardware is. However washed out colours could much easily be some undesirable setting in your settings especially colour, contrast or brightness including any video enhancements options so check your settings including in your GPU drivers. Note that for laptops, given the way they are normally used, may still have panels with poor viewing angles so it may matter a great deal if your watching straight on, or from the side (including the top or bottom) Nil Einne (talk) 04:04, 2 October 2021 (UTC)

Before you conclude it's specific to your machine, maybe you could provide an example link? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:35, 2 October 2021 (UTC)

Sounds like a driver issue. I'd suggest going to Lenovo's support site and downloading the newest graphics driver for your OS. Windows in particular often doesn't come with newest drivers out of the box. 93.136.33.168 (talk) 19:41, 4 October 2021 (UTC)

What does a changing magnetic field mean?

By definition, electromagnetic Induction is a current produced because of voltage production (electromotive force) due to a changing magnetic field.

If I take a bar magnet and spin at high speed so that magnetic field will change. Will it give me current according to this above definition? Rizosome (talk) 07:41, 2 October 2021 (UTC)

You need an electrically conductive circuit for a current to run. The spinning magnet and electrical circuit together form a primitive electric generator.  --Lambiam 08:28, 2 October 2021 (UTC)

Chances Hawaii will be destroyed by volcano?

As I understand it, some of Hawaiian islands are older than others, so they're further away from the most likely eruption spots. Are they relatively free from the likelihood of being destroyed by a super eruption? Are the newest islands in appreciable danger of being covered by a big eruption, or is the nature of the volcano island less dangerous? What about a tsunami? 74.64.73.24 (talk) 15:19, 2 October 2021 (UTC)

It appears that the Hawaiian islands are mostly Shield volcanos, which are not typically explosive like a Stratovolcano. But never say never. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:41, 2 October 2021 (UTC)

See here. Count Iblis (talk) 18:12, 2 October 2021 (UTC)

Nice. The more you know... 74.64.73.24 (talk) 02:35, 3 October 2021 (UTC)

See evolution of Hawaiian volcanoes and the Hilina Slump. There is also significant earthquake risk, see the 1868 Hawaii earthquake. Mikenorton (talk) 10:09, 4 October 2021 (UTC)

October 3

Do plants sleep under UV lamps?

Some botanists try to grow plants under UV lamps. At night time, does this plants sleep under those lamps or stay awake all the time? Sleeping means this oneRizosome (talk) 00:30, 3 October 2021 (UTC)

I'm going to guess not. Think marijuana farms. Imagine Reason (talk) 11:50, 3 October 2021 (UTC)

Maybe not a Reliable Source, but see Do plants sleep under ultaviolent rays?. A lot of other web sources are related to cannabis cultivation. Alansplodge (talk) 21:14, 3 October 2021 (UTC)

Relative volatility for ternary mixtures

What algebraic expression has the extension of the definition of relative volatility for ternary mixtures? Thanks!--178.138.98.154 (talk) 09:58, 3 October 2021 (UTC)

Raoult's law is written in terms of vapor pressure, but I think it can be pressed into service here. --Jayron32 20:46, 4 October 2021 (UTC)

Are N95 disposable respirators thicker than KN-95 ones?

I've tried a number of KN-95 respirators of various provenance. They seem to be of similar build and feel, and no one who've used them have been infected yet, so I assume they're decent. But they are relatively thin. I look at the 3M and Honeywell N95 respirators, with and without valves, and their layers seem more distinct, and thicker in total. I haven't seen anyone discuss this difference. Any ideas? Imagine Reason (talk) 22:41, 3 October 2021 (UTC)

The table on this page discusses the differences between the various standards (N95, KN95, P2, FFP2, etc.) I don't see "thickness" as part of any of the standards; N95 ones apparently are little bit more "breathable" than KN95. --jpgordon^{𝄢𝄆𝄐𝄇} 15:49, 5 October 2021 (UTC)

It's definitely not something that's discussed. I'm just curious because it seems obvious when you hold them side by side. Imagine Reason (talk) 15:08, 7 October 2021 (UTC)

October 4

How can a archaeologist tell whether dinosaur is carnivorous or herbivores?

How can a archaeologist tell whether dinosaur is carnivorous or herbivores just by seeing the skeleton? Rizosome (talk) 00:29, 4 October 2021 (UTC)

Probably by the nature of the teeth. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:58, 4 October 2021 (UTC)

See Biting#Types of teeth DuncanHill (talk) 01:04, 4 October 2021 (UTC)

One indirect clue is that there are a lot more fossil specimens of plant-eaters such as Hadrosauridae, then there are of carnivores. Lots more potential prey than predators. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:11, 4 October 2021 (UTC)

That is not a clue that can be used when seeking to classify a given dinosaur species, and an unnecessarily confusing comment.  --Lambiam 08:59, 4 October 2021 (UTC)

Wouldn't this be a paleontologist rather than an archeologist? -- Ross Burgess

Or even a Dentopaleontologist?? [6]. Martinevans123 (talk) 09:03, 4 October 2021 (UTC)

palaeodontology —Tamfang (talk) 00:45, 8 October 2021 (UTC)

As DuncanHill wrote, the classification is primarily based on the type of teeth found in fossils. For example, paleontologists suspect that dinosaurs in the genus Troodon were omnivores based on serrations on their teeth. The morphology (shape) of the jaws can be a further indication. Often, the classification (which can also include more specific classifications such as frugivore, insectivore and piscivore) is tentative, and different paleontologists may favour different hypotheses.  --Lambiam 09:21, 4 October 2021 (UTC)

FYI, archeology is generally about humans, and paleontology is general about non-humans. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:33, 4 October 2021 (UTC)

Specifically, paleontology "is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present)".

Archaeology is the study of "human prehistory and history, from the development of the first stone tools at Lomekwi in East Africa 3.3 million years ago up until recent decades".

Alansplodge (talk) 09:53, 4 October 2021 (UTC)

Note that the vegetation at the time was different, dominated by pine trees and conifers which are much tougher to chew on and digest than plants herbivores of today eat. Count Iblis (talk) 17:34, 4 October 2021 (UTC)

Never thought of that. Crazy. How did their digestive tracts handle all the sharp points? Imagine Reason (talk) 18:05, 4 October 2021 (UTC)

Lots of grinding before swallowing. Mikenorton (talk) 20:43, 4 October 2021 (UTC)

This Gastrolith#Gastroliths_in_paleontology may have helped in digestion as well. MarnetteD|Talk 22:39, 4 October 2021 (UTC)

... or else Fred and Wilma just took Dino downtown to get some tasty Pterodactyl ribs?? Martinevans123 (talk) 22:02, 4 October 2021 (UTC)

Nice one Martinevans123. We took my Mom to The Fort (Morrison, Colorado) for her 70th birthday. She ordered the buffalo ribs and when they brought them out those huge ribs next to my tiny Mom immediately brought that scene to mind :-P MarnetteD|Talk 22:39, 4 October 2021 (UTC)

What is it?

File:Insect to be identified.jpg

Hi, can anyone identify this insect? It was seen on a Buddleia bush in the south of England. ITookSomePhotos (talk) 17:33, 4 October 2021 (UTC)

Some form of hover fly, mimicking a wasp of hornet, perhaps a Volucella zonaria. Mikenorton (talk) 20:40, 4 October 2021 (UTC)

Thanks, yes it really does look very similar to the picture at that article. I see plenty of the smaller-size hoverflies, but I didn't realise any grew so big. ITookSomePhotos (talk) 21:06, 4 October 2021 (UTC)

Hornet mimic hoverfly says that it's "the largest hoverfly species in the UK" and "has become more common in Southern England in recent years... particularly prevalent in urban areas". Alansplodge (talk) 12:01, 5 October 2021 (UTC)

Is the fuel used for the Space Shuttle Challenger still used today?

I have read, or attempted to read, many articles on this subject, but I cannot figure this out. Thanks, Krok6kola (talk) 23:31, 4 October 2021 (UTC)

The fire coming out of the actual shuttle is just liquid hydrogen and oxygen, still used today. I think there's still a rocket sending men into orbit with kerosene and liquid oxygen (which is almost century old rocket oxidant, first distilled from air in the 1800s). High technology is not required, in the realm of fuel exoticness. Sagittarian Milky Way (talk) 00:28, 5 October 2021 (UTC)

My guess is that the OP is asking about the fuel used in the solid-rocket booster, since that was the bit that exploded. --Trovatore (talk) 00:39, 5 October 2021 (UTC)

Yes, that is what I am asking. Krok6kola (talk) 01:31, 5 October 2021 (UTC)

Our article on the Space Shuttle Solid Rocket Booster has a section called "Propellant", which explains that it used aluminum powder as the fuel, with an ammonium perchlorate oxidizer and an iron oxide catalyst, with some other ingredients. This is an ammonium perchlorate composite propellant; that article has a section on "Uses", but unless I missed it does not say whether the specific composition used in the Space Shuttle is still in use. --Trovatore (talk) 01:40, 5 October 2021 (UTC)

Not in use for the Space Shuttle, as it is retired, but used essentially unchanged (just more of it) for the boosters of the Shuttle derived SLS. EDIT: OK, I suppose technically that's not in use today, as it hasn't had it's first launch yet, but it's close enough Fgf10 (talk) 07:29, 5 October 2021 (UTC)

The cause of the disaster was a failing seal leading to a burn-through sending a flame to the external tank. This led to the explosion of the external tank, when the already compromised liquid hydrogen tank was pushed into the liquid oxygen tank. The original failure might have led to disaster with any type of potentially explosive propellant, but the boosters themselves did not explode. They remained mostly intact, except for a burn-through in one of the pair. (See Timeline of STS-51-L.)  --Lambiam 05:03, 5 October 2021 (UTC)

I have already read all that and already knew the above. I learned (via Netflix) that the Russians do no use solid fuel boosters. (Is that true?) I understand that the average Ph.D. in a science-based area (me), but not "hard" science, does not have the training to understand your articles on these subjects. And I still do not understand what Ammonium perchlorate composite propellant is from your articles, not for lack of trying. But thank you for taking the time to answer. Krok6kola (talk) 08:12, 5 October 2021 (UTC)

Perhaps you could add an item on the article's talk page about intelligibility, but note that the whole article has "multiple issues" and is a work-in-progress. Alansplodge (talk) 11:56, 5 October 2021 (UTC)

It isn't a great article, but really, not being able to read it and say what the stuff is? It isn't that bad. All you need is some very basic chemistry knowledge (my last chem class was as a freshman in college), and if you don't have that, then I'm not sure what sort of answer to "what the stuff is" you could understand anyway. --Trovatore (talk) 15:57, 5 October 2021 (UTC)

I don't have an academic degree, let alone a PhD, but I experienced no problem understanding Ammonium perchlorate composite propellant § Composition. IMO the article explains this quite clearly.  --Lambiam 09:16, 6 October 2021 (UTC)

Just to be very clear: "The cause of the disaster" were inexpert decisions made in advance, that led to a "failing seal". --87.147.178.162 (talk) 09:10, 5 October 2021 (UTC)

Or perhaps the cause was animals crawling ashore God knows how many million years ago. If they had just staid in the water, the disaster would not have happened.  --Lambiam 09:09, 6 October 2021 (UTC)

No, the failure of the O-ring was a direct consequence of launching in colder than recommended weather, presumably the decisions 87.147 refers to. Those are highly relevant to the accident, and mentioning them certainly doesn't deserve the mockery you gave them. Fgf10 (talk) 16:10, 6 October 2021 (UTC)

The failing seal was the proximate cause. It is too simple to state that the decisions were the cause, as if this is the only correct answer. We still don't know why precisely Aunt Minnie is in a hospital.^[7]

There is a whole book, The Challenger Launch Decision by sociologist Diane Vaughan, that studied the organizational processes leading up to the explosion. It was not just the cold weather launch, but the normalization of deviance stretching over many launches leading up to it. The O-ring that burned through on the doomed launch had burned partway through on earlier launches, but that was not seen as a failure since the Shuttle didn't explode. In fact it was not intended to burn at all, and should have been fixed as soon as any burn-through was noticed. The second half of Richard Feynman's memoir What Do You Care What Other People Think? discusses this at length. Feynman was on the commission that investigated the explosion and wrote up his experiences. He was the one who called public attention to the effects of cold weather on the O-ring.

As for rocket propellant, yes, I am pretty sure the aluminum/rust mix used in the Shuttle solid rocket boosters is a standard thing still used in solid rockets. However, I also believe (would have to check to be sure) that the Shuttle was the only US manned space launcher to use solid rocket boosters. The rest used only liquid fuels, which have higher specific impulse and can be throttled, but are more mechanically complicated. I do believe some Soviet manned launchers used solid boosters. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 08:41, 8 October 2021 (UTC)

October 5

Physics

What are the the reason for observing proper dressing while in a laboratory — Preceding unsigned comment added by 197.248.176.86 (talk) 03:30, 5 October 2021 (UTC)

What do you mean by "proper dressing"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:36, 5 October 2021 (UTC)

That it is improper to appear in an improper dressing? (I think this also applies to weddings, football matches and salads. Not exactly rocket science.)  --Lambiam 04:30, 5 October 2021 (UTC)

What did the oil-and-vinegar say when someone opened the refrigerator? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:02, 5 October 2021 (UTC)

While it depends on the laboratory, the appropriate garments and gear is needed to prevent or reduce injury in the event of a mishap. A lab coat is basic protection against chemical spills, and goggles may be necessary for eye protection. Personal protective equipment might be a good starting point.-gadfium 05:19, 5 October 2021 (UTC)

You may also have to be careful not to get hair in your experiment or dirt off your shoes into your equipment. When measure magnetic fields, it will be helpful not to have any metal objects on your person (eg keys, watches, phones, jewelry). So your experiments/equipment may need protection. Graeme Bartlett (talk) 10:15, 5 October 2021 (UTC)

See also cleanroom where special clothing is required to prevent contamination. Alansplodge (talk) 11:50, 5 October 2021 (UTC)

Why doesn't water fill the container if I do this?

If I submerge the container upside down, then water doesn't fill the container. Look at my image for more clear idea. Rizosome (talk) 07:07, 5 October 2021 (UTC)

The water can't fill the container because the air in the container has nowhere to go. If you made a small hole in the bottom of the container you will see the air bubble out the hole as water fills the container. 41.165.67.114 (talk) 08:02, 5 October 2021 (UTC)

This is precisely how an open-bottomed diving bell functions.--Shantavira|^{feed me} 08:34, 5 October 2021 (UTC)

See also Can pockets of air exist underwater?. Alansplodge (talk) 11:47, 5 October 2021 (UTC)

This is the mirror situation of an upright container filled with water. Why doesn't it spill out? In both cases the centre of mass would become lower by the change, so that is the preferred situation, the one with the lower potential energy. However, in either case the centre of mass needs to get temporarily higher before it can get lower, which is why the change does not happen. In the quantum realm it is possible by tunnelling, but not in the macroscopic world.  --Lambiam 20:53, 5 October 2021 (UTC)

As you push the container into the water the air gets compressed into the upper part of the container. The boundary of the region the air is in, is determined by the depth of the container, the surface tension of the water-container interface, the surface tension of the water-air interface, and the line tension of the water-container-air interface. Depending on the values of the surface and line tensions, what can happen if you push the container deeper and deeper into the water, is that the shape of the air inside will become concave, sagging at the container boundary and end up leaking out of the container from the edges when pushed deep enough into the water.

If this does not happen, the air will still gradually leak out by dissolving into the water. The concentration of air dissolved in the water is in thermodynamic equilibrium with the concentration of air at the surface. If you push the container into the water, then the air inside will be pressurized and therefore no longer in thermodynamic equilibrium with the dissolved air in the water. This will cause the air to gradually dissolve into the water. The concentration of air in the container will then increase, while the air pressure decreases. But no equilibrium will be reached where the pressurized air can remain. The larger concentration of air in the container compared to the air in the water outside of the container will cause the dissolved air inside the container to diffuse out of the container. So, in equilibrium, the concentration of the dissolved air inside the container will have to be the same as outside the container, which means that non of the trapped air can remain in the container in equilibrium. Count Iblis (talk) 21:43, 5 October 2021 (UTC)

But how does air escapes the container if I tip it to the side ? Rizosome (talk) 00:21, 6 October 2021 (UTC)

It has to slope a bit upward, the buoyancy force on the air then as a component in the direction toward the opening. Count Iblis (talk) 05:13, 6 October 2021 (UTC)

I am asking how air escapes in first case but not in the second case? see this image. In first case, I can see bubbles coming out of the container as water fills in. Rizosome (talk) 08:18, 6 October 2021 (UTC)

In case ① the air can move straight up to escape the cup. In case ②, it first has to move downwards to get across the rim before it can start moving up. See my answer above.  --Lambiam 09:02, 6 October 2021 (UTC)

In both cases, air is surrounded by fluid then why both cases are not equal? Rizosome (talk) 14:53, 6 October 2021 (UTC)

In the case of an upright cup filled with fluid, the air is not surrounded by fluid. The cases are then equal if you swap air (which has the lower density) and fluid (which has the higher density), and at the same time flip up and down. If you do the same swaps to image ①, the fluid will flow out.  --Lambiam 18:15, 6 October 2021 (UTC)

Just to be picky, air is a fluid, meaning it flows. Liquids and gases are both fluids. --Trovatore (talk) 17:57, 7 October 2021 (UTC)

The point is illustrated in this image, which is your ① | ② image except that I have swapped air and fluid and flipped it upside down. If you can understand why the fluid escapes on the left but not on the right for these fluid-filled cups immersed in air, you should be able to understand the same for the air-filled cups immersed in water.  --Lambiam 08:48, 7 October 2021 (UTC)

October 7

What is the pH of bad motel soap?

The kind that is a poor lubricant cause it's so alkaline it starts irritating after a few continuous minutes and hurts before an hour or so. Sagittarian Milky Way (talk) 02:32, 7 October 2021 (UTC)

I've never had that problem. Have you talked to a skin doctor about this? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:21, 7 October 2021 (UTC)

Did you ever get a silt-textured piece that's more alkaline than most soap sold in the first world? Sagittarian Milky Way (talk) 04:12, 7 October 2021 (UTC)

I don't know how I would be able to tell the chemical consistency of soap. But if a soap appears to be causing you skin problems, you should see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:25, 7 October 2021 (UTC)

Common supermarket soap isn't as bad. Sagittarian Milky Way (talk) 23:13, 7 October 2021 (UTC)

Then your best bet could be to take your own soap on trips that involve hotel stays. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:43, 7 October 2021 (UTC)

I'll probably regret asking this, but why would you be in contact with soap for "an hour or so"? --Trovatore (talk) 23:44, 7 October 2021 (UTC)

Maybe the OP just likes to be squeaky clean. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:04, 8 October 2021 (UTC)

The pH of the soap per se is not really meaningful as far as I know, but there are inexpensive universal indicator strips that you could carry around to test the pH of a concentrated aqueous suspension of the soap, such as you would find on the wet bar, if you ever happen to come across it again. --Trovatore (talk) 06:31, 7 October 2021 (UTC)

Are you sure it's the soap? I went to London and the water was so hard. It was very slippery and I couldn't rid the icky feeling while there. Imagine Reason (talk) 12:13, 7 October 2021 (UTC)

The slippery feeling is usually from soft water, not hard. Hard water precipitates out the soap so the soapy feeling goes away quickly; soft water doesn't, and you really have to work to get rid of the soap. --Trovatore (talk) 16:31, 7 October 2021 (UTC)

I have likewise experienced that. It makes the water feel "greasy". ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:49, 7 October 2021 (UTC)

The water in New York City is moderately hard in all Manhattan, most of coastal and South Bronx and a few nearby areas and soft everywhere else. The moderately hard area is only 3 million people. Sagittarian Milky Way (talk) 23:13, 7 October 2021 (UTC)

Soap used to alkaline because it was made from animal fat rendered in lye (sodium hydroxide), but I'd be surprised if that still existed post WW2 or so. Yes there are testing strips (maybe swimming pool supply places sell them) that let you measure pH conveniently. You can also use pink (or was it blue) litmus paper and see how quickly it changes color (stronger alkali = faster and stronger change). Or maybe you could mix a bit of soap solution with an acid such as vinegar, and see if it starts fizzing. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 08:56, 8 October 2021 (UTC)

Adam's Apple in Animals (specifically Great Apes)?

The article on Adam's Apple is entirely written in regards to Humans, is the extra swelling and/or deeper voice for males (which appears to be cause/effect) present in other animals, particularly in the great apes? The article on Larynx talks about differences between the Human Larynx and that of the great apes, but the differences by gender aren't part of that.Naraht (talk) 15:54, 7 October 2021 (UTC)

October 8

Why there is no "t" in this power formulae?

By definition, It is equal to the amount of work done divided by the time it takes to do the work. But in P= VI, I don't see "t" here. Why there is no "t" in this power formulae? Rizosome (talk) 02:52, 8 October 2021 (UTC)

Because the I is electric current, which is defined as the amount of electric charge moved divided by the time taken: I = Q/t. --184.144.99.72 (talk) 04:04, 8 October 2021 (UTC)

Rizosome, these are things you can easily find out yourself if you spend a little time researching the topic. Our article on electric power has a section Electric power § Definition that shows the following formula:

$P={\text{work done per unit time}}={\frac {W}{t}}={\frac {W}{Q}}{\frac {Q}{t}}=VI\,$

which explains how the $t$ "disappears".  --Lambiam 07:02, 8 October 2021 (UTC)

Ancestry genetics history of Turkmens & Circassians

Greetings,

Non–elite women's slavery in Ottoman Turkey has been one of my focus area of writing on WP. Turkish slavery was much different to Atlantic slavery. Ottoman Turkish slavery had high rates import and usage of slaves for domestic and war activities, manumission and social absorption of slaves.

This would have transformed Turkish genetic pool since pre−modern times. Present WP articles Turkmens and Circassians do not seem to offer any info on Ancestry genetics history of Turkmens & Circassians. But I suppose that must have been researched reasonably by now.

I came across articles Prehistoric Caucasus#Genetic history & Y-DNA haplogroups in populations of the Caucasus But for lay readers like me understanding Turkish & Circassian genetic pool and transformation in them since pre−modern times remains difficult.

From which end to start entangling these questions, can any sources be suggested?

Bookku, 'Encyclopedias = expanding information & knowledge' (talk) 05:06, 8 October 2021 (UTC)

Setting effects of slave imports apart, there are two competing theories about the dominant genetic origins of modern Turks. One is that they are mainly the descendants of the Oghuz clans (Turkmens) that settled in Anatolia after the Seljuk victory over the Byzantine Empire in 1071 in the Battle of Manzikert. The other is that they are mainly the descendants of the Anatolian population at the time, undergoing a gradual process of cultural Turkification. The first theory is mainly adhered to by Turkish nationalists who prefer to portray themselves as the descendants of glorious victors. It is not supported by the historical record, which does not indicate an unprecedented mass emigration or mass genocide of Anatolians in the late Middle Ages. Genetic studies of the present-day Anatolian population also showed a relatively low admixture of haplogroups of Central Asian origin. I don't have references ready, but if memory serves these studies were led by Cavalli-Sforza. I don't know if there is a basis for assuming a considerable and identifiable distinction between the 11th century Anatolian gene pool and that of the Caucasian (in the geographic sense) populations in the following centuries.  --Lambiam 06:53, 8 October 2021 (UTC)

We have an article on Genetic studies on Turkish people.  --Lambiam 07:04, 8 October 2021 (UTC)

Science

9. In a house there are six bulbs of 60 W each six of 40 Weach, and three of 11W each. All of them are used for 4 hours a day. How many units of electricity will be used up in 30 days? How much will they have to pay at 2.80 rupees per unit? — Preceding unsigned comment added by 106.220.124.171 (talk) 11:36, 8 October 2021 (UTC)

Is this a story problem from your school? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:55, 8 October 2021 (UTC)

Does look rather like a test question; suggest your answer should be: "There is insufficient information provided to answer this question; specifically a 'unit' would need to be defined." Chris (talk) 12:48, 8 October 2021 (UTC)