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July 17

Lorentz transformation vs Galileo

In special relativity, Einstein in a thought of mind shows that the time measured using a light pulse reflection between 2 points A and B in the same moving reference frame is not the same for an observer at rest and an observer in this mobile reference frame. In this case the speed of light is not taken into account, it is its constant value whatever the frame of reference which requires a Lorentz transformation. However, in another thought of mind, if I replace the reflection of a light pulse between the points A and B by an object in movement starting from A at constant speed and going to rebound on B by an elastic shock to return in A , that in A, then B, then A it emits a light pulse, in this case do we always use a Lorentz or Galileo transformation? Why would this variant of the mind's thought not be valid? Malypaet (talk) 03:53, 17 July 2023 (UTC)

What do you mean by "valid"? In one thought experiment, we flip a pancake and it falls flat on the floor. In another thought experiment, we flip a pancake and it gets stuck to the ceiling. Both are valid thought experiments.  --Lambiam 06:57, 17 July 2023 (UTC)

Your answer begs the question. Because if the second experiment is valid with Galileo's transformation, then it shows that the first is invalid for measuring time, that as a measuring instrument it has a bias due to the use of reflection on a mirror with speed referential independent, right? Do you have another interpretation? Malypaet (talk) 08:21, 17 July 2023 (UTC)

Lorentz transformations are always more accurate than Galileo transformations, but the errors introduced by using a Galileo transformation may be too small to matter. In the typical scenario with bouncing balls, using Galileo instead of Lorentz transformations gives you an error on the order of one in a billion. That's much smaller than your other sources of uncertainty and not worth the mathematical complexity of Lorentz transformations. PiusImpavidus (talk) 09:34, 17 July 2023 (UTC)

When a thought experiment is used, it is theoretically perfect and no accuracy errors occur. So can you explain to me your one in a billion error rate with the bouncing object? Malypaet (talk) 14:24, 17 July 2023 (UTC)

Your first thought experiment requires measurement of time between two flashes observed at one point, with no assumption of c. But your second thought experiment requires measurement of time between flashes emitted at A then at B. Can you tell us how fast the light travels to a common observing point for the time measurement? Philvoids (talk) 15:24, 17 July 2023 (UTC)

On the Electrodynamics of moving bodies extract:

"a ray of light proceeds from A at A-time tA towards B, arrives and is reflected from B at B-time tB, and returns to A at A-time t'A."

In my thought experiment:

"a ray of light proceeds from A synchronously with an object at A-time tA towards B, all 2 arrives at B that is a black body walls with perfect elastic properties so only the object is bounced from B at B-time tB and simultaneously proceeds a Ray of light, returns to A at A-time t'A and simultaneously proceeds a Ray of light."

In the 2 thought experiment, the observers read there clocks to get tA , tB and t'A.

The difference is that in the first case you need Lorentz transformation between observer at rest and the mobile one. In the second experiment as you have Galileo transformation, the clocks of the 2 observers are always synchronised, confirming Newton's absolute time.

What is false there ? Malypaet (talk) 19:32, 17 July 2023 (UTC)

I don't fully understand the thought experiment you propose. It seems that you assume that when moving objects are involved, you have to use Galileo transformations instead of Lorentz transformations. That's incorrect. You always use Lorentz transformations when the relative velocity of your frames of reference is a significant fraction of the speed of light. When dealing with electrodynamics, you may need Lorentz too. When playing a game of billiards, Galileo is good enough. PiusImpavidus (talk) 08:28, 18 July 2023 (UTC)

There's no explanation in your answer, just assertions based on articles I'm familiar with, but which don't address the case of the thought experiment I proposed. Lorentz transformations apply when using echoes of electromagnetic waves to measure the times of moving objects between different frames of reference. But, even if it is the most practical and precise method, it is theoretically not the only one available. If you are blind, time still passes and objects also move. Why don't you analyze my thought experiment in detail, contradicting it on every point or not? Malypaet (talk) 13:21, 18 July 2023 (UTC)

An object moves at constant speed from A to B to A, at each of these points emitting a light pulse. OK, but how is this a thought experiment? What is there to be analyzed?  --Lambiam 05:54, 19 July 2023 (UTC)

Based "On the Electrodynamics of moving bodies".

A thought experiment is an experiment that we imagine to validate a hypothesis and that we put in the form of a mathematical exercise, while waiting to be able to see it validated or not by a physics experiment or an observation in physics . For Einstein it came with Edington's observation and Pound and Rebka's experiment.

Here, in both cases, the times tA, tB and t'A are measured by a light pulse. On the other hand in the 1st case the object moving on a rod and reflected by a mirror is a light pulse with constant speed c whatever the referential, whereas in the second case the object which bounces on the mirror has a speed constant v1 only on the rod.

With the rod stationary, we have (tB - tA) = (t'A - tB) for all observers and in both cases, either (2 AB)/(t'A -tA)=c or (2 AB)/(t'A -tA)=v1 .

Now we consider the rod at speed v2.

In the 1st case for observer at rest we obtain:

(tB-tA)=rAB/(c-v2) and (t'A-tB)=rAB/(c+v2) => (tB-tA) # (t'A-tB)

Therefore, a Lorentz transformation is necessary between the observer at rest and the moving one.

In the second case for observer at rest we obtain:

(tB-tA)=rAB/(v1+v2) and (t'A-tB)=rAB/(v1-v2) => (tB-tA) = (t'A-tB)

Here just a Galilean transformation.

Voilà. Malypaet (talk) 13:01, 19 July 2023 (UTC)

Still not sure about the part thought experiment here. In both your functions, (tB-tA) = (t'A-tB) *(U+v2)/(U-v2), where U is either v1 or c. Rmvandijk (talk) 06:30, 20 July 2023 (UTC)

Well done for the illusionist trick with your U like a hat, but:

(tB-tA) = (t'A-tB) *(c+v2)/(c-v2)

&

(tB-tA) = (t'A-tB) *(v1-v2)/(v1+v2) Malypaet (talk) 20:34, 20 July 2023 (UTC)

However, I also made a mistake. In fact when my object goes from A to B, for the observer at rest it has the speed (v1+v2) and on the way back the speed (v1-v2), but on the way out point B moves away at the speed v2 and on the way back approaches at the speed v2.

So we get

tB-tA=rAB/((v1+v2)-v2) =rAB/v1

t'A-tB=rAB/((v1-v2) +v2) =rAB/v1

To resume your U, going U=v1+v2 and returning U=v1-v2 Malypaet (talk) 04:25, 21 July 2023 (UTC)

I correct by taking up Rmvandijk's idea. With for the observer at rest, going to B a speed of the object v'=v1+v2 and on the return v''=v1-v2, we obtain:

(tB-tA)=rAB/(v' -v2) and (t'A-tB)=rAB/(v''+v2) => (tB-tA) = (t'A-tB) Malypaet (talk) 04:44, 21 July 2023 (UTC)

Has there ever been a documented example of an animal using a weapon?

I don't know if you ever seen this, but this video has been doing the rounds for years online. Some soldiers were goofing around and gave an AK-47 to a monkey, which then proceeded to shoot at them and make them run away. It might be fake (I don't know), but I first saw it like 10 years ago. It turned up on my Youtube recs again tonight. Made me wonder - have there been any 100% confirmed, real examples of animals using weapons? For example, if a monkey picked up a thigh bone (as in 2001: A Space Odyssey), or a block of wood, or a rock, or whatever and bludgeoned another monkey to death in a fight. I know for sure that monkeys watch what people do and will do things like pick up smouldering dogends and smoke them, or drink the dregs out of people's beer bottles. How far does this go? Iloveparrots (talk) 23:58, 17 July 2023 (UTC)

As noted in Tool use by non-humans (WP:WHAAOE strikes again), it was discovered in 2007 that chimps use sharpened sticks while hunting. There's an unsourced claim there that "This is considered the first evidence of systematic use of weapons in a species other than humans." Sea otters routinely use rocks to smash open their food/prey. Clarityfiend (talk) 00:23, 18 July 2023 (UTC)

"Research in 2007 showed that common chimpanzees sharpen sticks to use as weapons when hunting mammals. This is considered the first evidence of systematic use of weapons in a species other than humans" - I see, thank you.

Another thing I was wondering from watching the breeding birds around here, and I'm not sure if this has ever happened. Although birds often work together to chase away hawks from their breeding colonies when the hawk appears - have the birds (crows for example) ever thought, after that, to figure out where the hawk lives and then send (say) 20 of the strongest males from the colony to take it out while it was least expecting it? Iloveparrots (talk) 01:07, 18 July 2023 (UTC)

While I am not an expert ornithologist (so am very open to correction), not only have I never heard of such a thing (in over half a century of reading about natural history), but everything I (think I) know about avian cognition suggests such high-level reasoning, communication and co-operation would be considerably above even the most intelligent birds' capabilities.

Obviously, finding a reliable reference that a thing that has never been observed has not, in fact, ever been observed is problematical. {The poster formerly known as 87.81.230.195} 51.198.140.169 (talk) 05:34, 18 July 2023 (UTC)

George Orwell composed an anthem "Beasts of England" to incite animals on a farm including hens, ducks, roosters and geese to revolution. Philvoids (talk) 10:49, 18 July 2023 (UTC)

He did, but the work clearly falls into the genre of Fable, so is not a reliable reflection of real-world natural behavior. (Taking off my pedant hat, I am a lifelong fan of non-realistic genres.) {The poster formerly known as 87.81.230.195} 51.198.140.169 (talk) 00:44, 19 July 2023 (UTC)

I think, from reading about corvids that this is the case: individual corvids sometimes collect food items (nuts and seeds, for example) and store them by burying them in the ground or hiding them in tree hollows with the expectation that they will be able to collect them later, say in winter, when food is scarce. Some do it, some don't - but they are at least somewhat capable of realizing that actions committed today may influence future events (but it doesn't happen that often). But it is never the case that the entire flock works together to gather and store food and (say) keeps it in one place which is then guarded by the entire flock, in order that they all may benefit from the food in winter. Iloveparrots (talk) 19:24, 19 July 2023 (UTC)

Well, many animals cache food but I don't think we can assume that the behavior is indicative of planning rather than instinct. My pet rats, when offered food, will usually grab it and immediately run and hide it. I don't think it indicates planning or a deliberative thought process, it's just an instinct to hide food that one is not going to eat right now. Some individual rats seems to have a stronger caching instinct than others though. CodeTalker (talk) 20:55, 19 July 2023 (UTC)

I don't really think that animals really have much of an understanding that actions committed in the past may have consequences in the present, or that actions committed in the present may influence the future. There have been occasional studies, like with the Tanimbar corella that demonstrated that they can reject food items if they are aware that they will be awarded with superior food items in the future - but that is literally talking about minutes later, not weeks or months. I'm well aware that punishing a pet dog for something like damaging furniture, ripping up the wallpaper, or peeing on the carpet by yelling at it, cuffing it upside the head or sticking a boot up its ass (please don't do this - but people do, talking from personal experience) doesn't work at all because they are literally unable to make the connection between something that happened a couple of hours ago and now. Iloveparrots (talk) 21:21, 19 July 2023 (UTC)

I have read about corvids not only caching food for later consumption, but also pretending to hide food if they know they are being watched. This article mentions it, along with other claims about the intelligence of corvids, although it doesn't have any references. Turner Street (talk) 14:40, 21 July 2023 (UTC)

I didn't find a source, so take it with a grain of salt: A group of baboons attacked a leopard using rocks. Zarnivop (talk) 08:25, 18 July 2023 (UTC)

Orcas use directed waves to dislodge prey from icebergs. BBC Earth, via Youtube Bazza (talk) 08:33, 18 July 2023 (UTC)

If the future's dystopic enough someone will invent gorilla guerillas. Driving the cyborg body like a video game or gene editing it to the intelligence, fine motor skills and brainwashability of a child soldier without loss of muscularity or possibly just extremely good selective breeding and training. And AK-style rifles with giant levers or whatever's the easiest trigger for gorillas to use. Also someone will invent 2 millimeter spy roaches. With cameras in shop ceiling-like fake eye globes and Wifi for brain-interface and live video. Sagittarian Milky Way (talk) 18:42, 18 July 2023 (UTC)

I don't know if you ever seen this, but this video has been doing the rounds for years online. Some soldiers were goofing around and gave an AK-47 to a monkey, which then proceeded to shoot at them and make them run away. It might be fake (I don't know), but I first saw it like 10 years ago.

It's 100% fake. The video you refer to, "Ape with AK-47", is a viral video campaign created by ad agency Mekanism on behalf of their client 20th Century Fox to promote the 2011 film Rise of the Planet of the Apes. Viriditas (talk) 23:38, 18 July 2023 (UTC)

There was an ISIS video where they had a chimpanzee execute a hostage with an SKS. McAynus (talk) 02:24, 19 July 2023 (UTC)

Google says nary a word about it. Viriditas (talk) 02:31, 19 July 2023 (UTC)

I suspect that any extended searching of ISIS videos might bring you to the attention of the security services. Alansplodge (talk) 11:44, 19 July 2023 (UTC)

Well, if you consider Homo sapiens being a species in the animal kingdom... --CiaPan (talk) 20:16, 19 July 2023 (UTC)

July 19

Magnesium Sulphate

Last year, I bought some magnesium sulphate paste for removing splinters. Now it has separated into a hard, crystalline, mass and some clear liquid resembling glycerine. Is there any way of returning it to a paste or do I have to buy some more? Alansplodge (talk) 10:52, 19 July 2023 (UTC)

Magnesium Sulphate Paste is literally just magnesium sulphate and glycerine, with a small amount of phenol. Here is a typical ingredient list, but I've checked several others, and that's what it is. It hasn't "gone off" or anything, the magnesium sulphate has just settled out of the suspension (which is what a "paste" generally is, from a chemistry point of view). Depending on how much effort you want to put in (vis a vis the cost of just buying more) you should be able to just remix the ingredients. --Jayron32 11:36, 19 July 2023 (UTC)

Thanks Jayron. The problem is that the solid part has the consistency of concrete and has so far resisted my remixing efforts. Would heating it help? Alansplodge (talk) 11:42, 19 July 2023 (UTC)

Possibly, gentle heating would help. IIRC, magnesium sulphate is usually a fairly well-hydrated crystal, and gentle heating may help release some of the "waters of hydration", possibly enough to dissolve it slightly and help break it up (see Epsom salt). If that doesn't work, perhaps something like a kitchen blender or food processor may help? If you don't have anything like that, I'm at a loss. --Jayron32 11:48, 19 July 2023 (UTC)

Bingo! I pinged it in the microwave - worked like a charm. Many thanks. Alansplodge (talk) 12:50, 19 July 2023 (UTC)

Resolved

Evolution of birds from dinosaurs

As far as I'm aware, the current scientific consensus is that modern birds evolved from the tiny number of dinosaurs that survived the Chicxulub impact. However, it is somewhat unclear to me - did birds, as we know them now exist *before* the meteorite hit, or did they emerge later? At school, I was taught that all mammals evolved from a small number of tiny rat-like creatures (in terms of body form) that somehow survived the apocalypse - and that all birds evolved from a small number of tiny velociraptor-like creatures (in terms of body form) that somehow survived the apocalypse - but I think from my readings that this is inaccurate now? Iloveparrots (talk) 21:50, 19 July 2023 (UTC)

See the related articles Origin of birds and Evolution of birds. The evolutionary events that gave rise to the early birds within maniraptoran theropods and the origin of bird flight are disputed questions. Philvoids (talk) 22:35, 19 July 2023 (UTC)

Today's birds form the class Aves, which is a subset of the clade Ornithurae. This clade also includes two extinct genera of bird-like reptilians.  --Lambiam 22:39, 19 July 2023 (UTC)

Birds evolved before the end-Cretaceous extinction event, although exactly how much before depends on how you define "birds". If "birds" means "the most recent common ancestor of all living birds and all of it descendants", then birds first appeared some time in the Cretaceous. If "bird" is defined more broadly to include Archaeopteryx, then they evolved in the Jurassic. Iapetus (talk) 12:30, 20 July 2023 (UTC)

(edit conflict) To build on the excellent answers above, and to directly answer the question "did birds, as we know them now exist *before* the meteorite hit, or did they emerge later?" four clades of birds are believed to have existed prior to the Cretaceous–Paleogene extinction event that killed off the non-avian dinosaurs, which is to say that the "most recent common ancestor" of all modern birds predates the extinction event by some time. Roughly speaking, those clades are the "big fat running birds" of the ostrich-emu-cassowary type, "waterfowl" like ducks and geese, "groundfowl" like chickens and turkeys and peafowl, and "everything else". It is thought that these divisions among birds (or bird-like dinosaurs or whatever term you wish to use) existed prior to the extinction event. You can find a partial list of such birds at Category:Mesozoic birds. Also as noted, the exact nature of mesozoic bird evolution is unresolved; there are several competing theories, but all we do know is that whatever happened to give us birds, it certainly happened prior to the extinction event that took out the rest of the dinosaurs. --Jayron32 12:31, 20 July 2023 (UTC)

As for mammals, see Evolution of mammals. --User:Khajidha (talk) (contributions) 13:16, 21 July 2023 (UTC)

GF's question:

My girlfriend wants to know what is the world's largest penis, and I'm NOT talking about porn. (She caught me editing on Wikipedia and got curious about Wikipedia as well ) I'm talking about human penises. 😺😘🥰 Nuclear Sergeant (talk) 22:57, 19 July 2023 (UTC)

See the article Human penis size and a claim of Jonah Falcon. Philvoids (talk) 01:46, 20 July 2023 (UTC)

Or this:[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:59, 20 July 2023 (UTC)

According to Wikipedia, the penis on a right whale can be up to 2.7 m (8.9 ft) Shantavira|^{feed me} 07:59, 20 July 2023 (UTC)

July 20

Blackbody emission questions.

1. Almost everything with heat emits IR. Humans, animals, water. The biggest source is the sun and fire. But I'm trying to find out who doesn't emit IR in darkness. I suppose humans and animals emit IR in darkness, but not water?

2. As sunlight is 52-55% IR and causes water to emit IR, I'm also curious to know how we draw the line between Blackbody radiation, and fluorescence/phosphorescence, of IR. Things that absorb IR, and emit in deep-IR. The thing is, if water stops emitting IR as soon as darkness, then that is equivalent to fluorescence, and if water emits for another 10 seconds after darkness, that's equivalent to phosphorescence.

3. They say most things that Blackbody IR at room temperature, will emit light, starting at red light, at 500 C. But what material is that, I've never found a chart for different materials such as steel, plastic, water (albeit some will turn liquid or gas 1st). What are some Blackbodys that have the lowest temperature to emit visible light? Thanks. 170.76.231.162 (talk) 16:17, 20 July 2023 (UTC).

The maximum wavelength of emission depends on the temperature

All objects emit light, so long as they have a temperature, so ANY thing with a higher temperature than absolute zero will emit light. The specific spectrum of light that object emits is basically dependent only on the temperature, so long as the only source of light is from thermal radiation (there are OTHER processes that will emit light as well; the point of a blackbody is that it is an idealized object that can only emit thermal radiation. Simply put, all objects with any temperature at all emit thermal radiation; that thermal radiation (light wavelengths) fill follow a type of normal distribution probability distribution edit: The previous term was corrected from the original writing, which used an incorrect term. --Jayron32 11:05, 21 July 2023 (UTC) whose central limit is dependent on the temperature. In simple terms, the frequency distribution of the light will have the shape of a curve shown at right, with frequency on the X axis and intensity on the Y axis; the peak of the curve will be shifted further right for hotter objects and left for cooler objects. As some examples of this temperature dependence, humans have a temperature on order of about 300ish K, which corresponds to a frequency distribution whose peak is in the infrared. However, something like a lightbulb filament has a temperature on order of about 5000 K, which corresponds to an peak frequency somewhere near the middle of the visible range. If you look at the cosmic microwave background, which is basically the "temperature of space", it's about 3 K, which corresponds to a frequency peak in the (you guessed it) microwave range. However, it's important to note that this is a distribution and not a singular monochromatic light. The exact distribution (from which you could work out the relative amounts of each frequency of emitted light) is given by Planck's law. --Jayron32 16:35, 20 July 2023 (UTC)

Excellent answer, except for the bit about the normal distribution, which seems out of place here. Did you mean to refer to a more general term, like probability distribution? --Wrongfilter (talk) 10:03, 21 July 2023 (UTC)

Yes, I chose the wrong term. Thank you for the correction. I have fixed it. --Jayron32 11:05, 21 July 2023 (UTC)

I would drop any reference to the Central limit theorem that is not useful here where the simple expression "peak (of the curve)" is well understood. Philvoids (talk) 16:46, 21 July 2023 (UTC)

I have no idea how to calculate this, but there must be a minimum yet greater than zero Kelvin temperature which under it no light will be emitted. A single photon of the longest wave light (deep red) has a fixed energy. When the energy of light is under that threshold, no light will be emitted. Zarnivop (talk) 17:21, 20 July 2023 (UTC)

Not necessarily. The limit is set by Planck's constant, which merely states that the smallest unit of light is the photon, but a single photon can have any arbitrarily small frequency of light. E = hν, so for any frequency of light, the smallest amount of energy for that frequency is just Planck's constant times the frequency, but there is no lower limit on frequency. "Deep red" is still very high frequency light, with wavelengths on the order of a micrometer (1 millionth of a meter) or so. The CMB light has wavelengths of cm scale, however meter-length wavelengths or longer are perfectly common. VHF frequency radio waves have wavelengths in the meter-to-tens of meters range, while light with wavelengths as long as hundreds of thousands of kilometers (see ELF) which have been used to practical effect by humans. There is no functional "longest wavelength of light". There is a functional "Smallest quantum of energy for a given wavelength" (the photon) but that's not the same thing. --Jayron32 17:37, 20 July 2023 (UTC)

Also, the light is emitted by a system of atoms, not by a single atom. If you've got 10²³ atoms forming a solid with a temperature of a few kelvin, there's more than enough thermal energy to emit a single visible photon. It's not very likely to happen though. PiusImpavidus (talk) 19:33, 20 July 2023 (UTC)

Light is by definition is bound between red (or at most IR) and purple (or at most UV). Radio frequencies are not light. Both are EM radiation, but you stated that anything above absolute 0 emits light. This is not true. EDIT: Anything above absolute zero emits photons, but not every photon is light - that depends on its energy. Zarnivop (talk) 22:27, 20 July 2023 (UTC)

Engineering may have such a definition, but physics does not. In astronomy, we usually refer to ultraviolet and infrared radiation as "light", as the detector technology is basically the same as for "visible light", but if the mood takes us then light can occasionally mean all of em radiation. --Wrongfilter (talk) 10:03, 21 July 2023 (UTC)

That's a rather facile understanding of light, and does not represent actual reality. There's nothing especially different between red light and radio waves, at all, except for the rather unimportant distinctions made by human biology. Since we aren't discussing human biology in this discussion, such distinctions aren't relevant. Clearly, putting such arbitrary distinctions on the discussion does not help answer the question correctly, which is why it isn't appropriate to do so. --Jayron32 11:02, 21 July 2023 (UTC)

Do astronomers refer to radio frequencies as "light", I can totally see them include UV and IR, but I doubt anything else like radio, be it "facial" or whatnot. Zarnivop (talk) 13:53, 21 July 2023 (UTC)

"facetious"? It's probably used very rarely when talking about radio specifically, but when somebody says "We get most of our information on the universe in the form of light", I would naturally understand radio as part of that (but not gravitational waves or neutrinos). But I admit this is a personal impression and I'm not going to look for references. --Wrongfilter (talk) 14:41, 21 July 2023 (UTC)

I believe Jayron32 means FACILE adj. too simple to deal with the difficulties of a real situation, arrived at without due care or effort; lacking depth. I am unlikely to tell my grandmother that her cellphone works by sending light beams, nor should she expect to be lectured to by her grandchild that any doubt on this matter is merely due to her unimportant arbitrary, unreal and incorrect biological shallowness. Wrongfilter and Zamivop's comments correctly and appropriately remind us that in the vernacular English understood by the majority of general readers, and by all English speakers before Maxwell's demonstration in 1865 of the electromagnetic field, the word "light" means principally visible light. I think we can all distinguish between RADAR and LIDAR. Philvoids (talk) 21:03, 21 July 2023 (UTC)

I took upon myself to replace the image given here with the actual graph. The old graph accurately depicted that the maximum-emission wavelength changed with temperature, but (wrongly) implied that for a given wavelength, an increase of temperature could decrease the emission. That is not true - for all wavelengths, spectral emissivity increases with temperature. Tigraan^{Click here for my talk page ("private" contact)} 08:44, 21 July 2023 (UTC)

On the original question it should be pointed out that fluorescence and phosphorescence are line emissions, light is emitted only at certain wavelengths/frequencies given by electronic transitions in atoms or molecules. Thermal emission on the other hand is continuous emission, i.e. light is emitted at any wavelength (in any real situation probably better described as quasi-continuous). These are rather different processes. --Wrongfilter (talk) 10:03, 21 July 2023 (UTC)

July 21

In two bottles of different volume, both emptied up to a vacuum, is the pressure on the seal of each the same?

In two bottles of different volume, both emptied up to a vacuum, is the pressure on the seal of each the same? Bumptump (talk) 01:00, 21 July 2023 (UTC)

I'd think so. Thought experiment: what causes the presssure? What mechanism would increase or decrease said pressure based upon the contents (or absence thereof) of the bottles? --jpgordon^{𝄢𝄆𝄐𝄇} 01:34, 21 July 2023 (UTC)

Assuming they're sitting next to each other, presumably each would experience the same air pressure. Are you thinking that the larger bottle would have more "suction" than the smaller one? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:15, 21 July 2023 (UTC)

I assume "emptied up to a vacuum" means that the sealed bottles each contain vacuum, and you're asking about the pressure exerted by the surrounding atmosphere. Then there are a couple of things to consider. First, since the atmosphere has weight, the atmospheric pressure varies according to altitude, so if one of the bottles is placed higher, then the pressure on it will be reduced. And second, it's not clear whether the original poster was asking about "pressure" in its proper technical sense (referring to the amount of force per unit area), or in the informal English sense where it just means a force that presses. If the pressure in the technical sense is the same on both bottles (the air is at the same altitude and temperature), then the force on the larger seal will be larger in proportion to its area.

In any case, the volume of the bottles is irrelevant. --142.112.221.64 (talk) 05:19, 21 July 2023 (UTC)

Why does electrocution stop after a few seconds in a bug zapper?

I have observed that when an insect is electrocuted in a bug zapper, there are typically a few sparks or flashes of light. Sometimes the insect will catch on flame in a tiny fire, and the body will burn for a few seconds before stopping burning. The lights and flames stop after a few seconds, but the insect body often, instead of falling, remains in position still connecting two wires.

Given that the body is still in position connecting two wires, why is it that after a few seconds, sparks or flashes of light stop appearing, and any fire is extinguished? Does that mean that electricity is no longer flowing through the insect's body, and if so, why does the electricity stop flowing if the body is still connecting the two wires?

—SeekingAnswers (reply) 05:48, 21 July 2023 (UTC)

Maybe once their little carcasses are dried up, they can't conduct electricity? Abductive (reasoning) 06:55, 21 July 2023 (UTC)

That is very likely the main cause - the corpse becomes non-conductive because it dries and burns up.

Another possibility (which, again, is less likely in my semi-informed opinion) is that the bug zapper needs time to recharge. A bug zapper is a discharge circuit where a capacitor is slowly charged when the circuit is open and then quickly discharged when the circuit is closed (by the poor insect). The charge time can be a couple of seconds while the discharge is much quicker (millisecond or lower) - but it’s hard to tell without a spec sheet of the electrical circuit, which I did not find in a quick online search.

Yes, discharge circuit is a redlink. Wikipedia does not have an article about everything, apparently. We have articles about Capacitor discharge ignition, cattle prod, bug zapper etc. but none of those give an electrical diagram. Tigraan^{Click here for my talk page ("private" contact)} 09:24, 21 July 2023 (UTC)

I can't see how it could be the latter explanation, because all the bug zappers I've ever seen have virtually instantaneous "recovery" times, being able to zap multiple different insects seemingly simultaneously, and the dead insects often remain stuck between wires indefinitely without ever falling or reigniting even hours or days later.

So, a couple of additional questions arising from the first explanation: First, how exactly does electrocution cause drying: is it that electrocution generates heat, which causes the water to evaporate away into the air? And second, does that mean that organic tissue is nonconductive without water?

—SeekingAnswers (reply) 16:20, 21 July 2023 (UTC)

2023 Annular Eclipse...

... Of the sun due to take place in Oct. Of 2023. Just got this from a few news outlets. Some even have a map of the US, showing the path of the eclipse, and the time it'll take place. Is there info. On it here? Can this be used as a source? Thanks. 😺😺😺😺😘🥰 Nuclear Sergeant (talk) 11:45, 21 July 2023 (UTC)

See Solar eclipse of October 14, 2023.

• Did you know: we have almost half a million articles tagged with "citation needed" somewhere in the text? I mean, if you're keen to find a source and have it used in an article, those are some of the ones that need sources. Solar eclipse, for instance, is tagged in two places.  Card Zero  (talk) 11:50, 21 July 2023 (UTC)

Chokeberries

What may cause the tobacco-like smell of chokeberries and juice made of them? Are there, perhaps, some chemical compounds of same type in both the berries and tobacco plants? --2001:999:404:7509:5AE3:4A4:DD10:8B49 (talk) 13:15, 21 July 2023 (UTC)

Aronia#Polyphenols has some info. Abductive (reasoning) 00:00, 22 July 2023 (UTC)

Paired samples

 Note: For those interested (since there seems to be some slack there) – feel free to comment ideally within that thread. Best, Hildeoc (talk) 13:44, 21 July 2023 (UTC)

July 23

Draining water from a sink without swirling

Could we create a sink so solid and precisely crafted, up to fractions of mm, that water sinks straight down, without swirling? Or would that be like stacking 20 M&M's on top of each other? Bumptump (talk) 18:19, 23 July 2023 (UTC)

The construction of the sink is irrelevant. There will always be eddies that will produce a vortex. Shantavira|^{feed me} 18:26, 23 July 2023 (UTC)

So, even on a non-rotating Earth, not to speak of on a flat Earth, we'll get a vortex? --Bumptump (talk) 22:01, 23 July 2023 (UTC)