Wikipedia:Reference desk/Archives/Science/2023 September 7

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September 7

What does 'c.' before a length mean in text?

I've found this sentence here, "The tawa forest is affected by a cloud cap that forms above c. 400 m, causing increased precipitation" but I cannot seem to figure out what this 'c.' means. My first guess was sea level, but I can't find any evidence supporting this. I also thought that it could mean "cubic", but it doesn't seem to make any sense in this sentence. What does the 'c.' stand for?

Source: https://doi.org/10.1080/03014223.2005.9518421 Panamitsu (talk) 00:01, 7 September 2023 (UTC)

"Approximately": it is an abbreviation of "circa" see wikt:c.#English for our dictionary entry. Graeme Bartlett (talk) 00:22, 7 September 2023 (UTC)

"ca." is also used. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:49, 7 September 2023 (UTC)

See MOS:CIRCA – "To indicate "around", "approximately", or "about", the use of the {{circa}} template is preferred over circa, c, c., ca, ca., around, approximately, or approx.:". Martin of Sheffield (talk) 08:58, 7 September 2023 (UTC)

MOS:CIRCA is about dates. And my experience ("in the wild", if you will) with "circa" has also been mostly (nearly entirely, actually) in reference to dates. This usage with a measurement seems decidedly weird to me. I would suggest changing to "approximately" in this case. --User:Khajidha (talk) (contributions) 14:05, 7 September 2023 (UTC)

I agree that c. should (almost) exclusively be used for dates. In my experience, ~ (tilde) is generally used for approximate numbers otherwise. 136.54.106.120 (talk) 18:26, 7 September 2023 (UTC)

Tildes look strange in running prose, as in, "In France, the Communists may expect ~ twenty percent of the vote."^[1]  --Lambiam 02:11, 8 September 2023 (UTC)

If you're going to spell out "twenty" and "percent", then it certainly would look strange to use a symbol for "approximately". 136.54.106.120 (talk) 04:43, 8 September 2023 (UTC)

That's why we have the words "about", "approximately", and "roughly". --User:Khajidha (talk) (contributions) 05:20, 8 September 2023 (UTC)

I'd go with "around" in that specific context, since it suggests (to me anyway) that it varies from one occasion to the next. AndyTheGrump (talk) 05:39, 8 September 2023 (UTC)

You can use "abt" to shorten "about". ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:56, 8 September 2023 (UTC)

But don't do that on Wikipedia articles. Graeme Bartlett (talk) 11:10, 8 September 2023 (UTC)

In the context of wikipedia articles, it's better to spell things out. 14:13, 8 September 2023 (UTC)←Baseball Bugs ^{What's up, Doc?} carrots→

Origin of physics thought experiments

I'm trying to find the original source of a physics thought experiment. That's the one in which two cars, same mass, same speed, collide frontally, compared to a car that collides with an unmovable, indeformable block. Somehow it seems pretty common among students of physics, but does not appear to have a name. Bumptump (talk) 16:51, 7 September 2023 (UTC)

It is an accurate model of a collison between two identical cars, and has been used since 1959 if not before. I'm not quite sure why a bog standard bit of Newtonian physics would have a name. Greglocock (talk) 22:43, 7 September 2023 (UTC)

Per Head-on_collision#Road_transport While it is true (via Galilean relativity) that a head-on crash between two vehicles traveling at 50 mph is equivalent to a moving vehicle running into a stationary one at 100 mph, it is clear from basic Newtonian Physics that if the stationary vehicle is replaced with a solid wall or other stationary near-immovable object such as a bridge abutment, then the equivalent collision is one in which the moving vehicle is only traveling at 50 mph., except for the case of a lighter car colliding with a heavier one. Shantavira|^{feed me} 08:27, 8 September 2023 (UTC)

I hereby dub thee the "car collision conundrum" (c³), exponentially more interesting than that equation with a mere c². Clarityfiend (talk) 02:03, 9 September 2023 (UTC)

The equivalence only holds perfectly if the cars are each other's mirror image, so if one has the steering wheel on the left, the other has it on the right. An observer should be unable to tell if there are two cars or one car and a gigantic mirror showing the mirror image. The equivalence then follows from the preservation of symmetry. We see the same with animals fighting their own mirror images. The animal cannot sense the difference between hitting an immovable mirror and each of its moves being perfectly copied and thereby parried by an opponent.  --Lambiam 07:40, 9 September 2023 (UTC)

A true mirror-image replica of the car you plan to crash is probably available at a high price and a long delivery time, mainly due to the unusual need for reversed items such as brand badge castings, contra-rotating engine parts and all the dashbord instruments including mirrored lettering on the retemodeeps. Philvoids (talk) 16:58, 10 September 2023 (UTC)

Earth's magnetic field functionality over time

On a scale of thousands or millions of years, do the changes in the strength of Earth's magnetic field significantly affect (deteriorate or improve) its protective ability to deflect most of the solar wind? 212.180.235.46 (talk) 21:38, 7 September 2023 (UTC)

Yes — see Geomagnetic excursion and Laschamp event for speculation. More Beryllium-10 would be produced, but our article is lacking info on your timescale of interest. Graeme Bartlett (talk) 22:28, 7 September 2023 (UTC)

Convection cells

What factors determine how many a planet has? Sagittarian Milky Way (talk) 22:48, 7 September 2023 (UTC)

I imagine there is an optimal size. Per Atmospheric circulation they are, fundamentally, a property of the Earth's size, rotation rate, heating and atmospheric depth, all of which change little. Shantavira|^{feed me} 08:16, 8 September 2023 (UTC)

So which directions increase number and which decrease? Does Jupiter have so many cause it's big or has high Coriolis force or is hot inside or cold outside or thick skinned or some combination of that? Sagittarian Milky Way (talk) 12:31, 8 September 2023 (UTC)

I suspect that such convection cells are likely complex and chaotic behavior, likely obeying something akin to the Logistic map in terms of having islands of stability in the midst of otherwise chaotic behavior. --Jayron32 13:29, 8 September 2023 (UTC)

I think that the number of cells is primary determined by ratio of the Coriolis force to the gravity acceleration. So, the fast rotators like Jupiter have many convective cells, while slow rotators like Venus and Titan have only one convective cell. Earth is somewhere in the middle. Ruslik_Zero 20:32, 9 September 2023 (UTC)

The Coriolis force in turn depends on the spin rate of the planet and on the wind speed. When there's more heat to move from the equator to the poles (warm planet) or when less heat can be moved per cubic metre of atmosphere (thin air), the wind will be faster. Oceans may matter too: if there's an ocean with strong north-south currents, more heat can be transported by the oceans, so less will be transported by air. I think there could be planets where, due to continental drift affecting ocean currents, the atmosphere can alternate between multiple numbers of cells over geological timespans.

To find the number of convection cells on a particular planet (other than from observation), you may have to perform a full simulation with a model of ocean and atmosphere. Even then, you may find a bistable situation, where depending on history the circulation may be in either of two states. PiusImpavidus (talk) 10:18, 10 September 2023 (UTC)

Methamphetamine questions

Let me preface this by saying that I'm not asking for step-by-step instructions on how to make meth (I don't even smoke cigarettes any more), but I recently rewatched Breaking Bad (as you all should) and I was curious about a few things. Mainly with regards to accuracy - thought I'd bring it here.

1. How much would a methamphetamine chef *actually* make in the real world, on average?

2. Has there ever actually been an example of a huge secret meth lab that produces the stuff on an industrial scale, as seen with Gus Fring's lab?

3. Producing a 99% pure methamphetamine using the principal method used by Walter as shown in the show (phenylacetone and methylamine reaction) is apparently impossible in the real world - going from what I remember reading on forums and Reddit back in the day where chemists and actual former meth cooks were discussing this, something due to contamination with unwanted/useless isomers. That what is show in the show is pure science fiction. Is that still true? In the show it's kinda implied that Walter has found a way around this and no-one else knows how to do it, but it's never actually explained.

Thanks. Iloveparrots (talk) 23:08, 7 September 2023 (UTC)

Most of these questions are answered or can be inferred from our article History and culture of substituted amphetamines#Illegal synthesis. Mike Turnbull (talk) 11:12, 8 September 2023 (UTC)

A friend has pointed out to me that, according to IMDB (not a Reliable source), the writers intentionally made Walter's portrayed method non-viable so that would-be criminals could not use it. {The poster formerly known as 87.81 230.195} 51.194.81.165 (talk) 18:39, 9 September 2023 (UTC)

Indeed. As a chemist, I absolutely love how the writers danced that fine line between "scientifically accurate depiction of how chemical synthesis is done" and "don't tell would be 'cooks' how to make meth." I honestly feel they did a fantastic job at it, down to little bits that we see in notebooks and the like. Oftentimes, as a chemist, I lose the ability to "suspend disbelief" because a show or movie does something blatantly wrong or impossible, such as in Wonder Woman, when the villains are described as making mustard gas much more potent by "replacing the sulfur atom with a hydrogen atom." They would have been better off just saying the villains had made a chemical weapon "ten times worse than mustard gas" and leaving it at that, without describing the method or change. A hydrogen atom literally cannot go in place of the sulfur and have the molecule stay together and do anything. When I watch Breaking Bad, the depictions are so faithful to real world chemistry and chemical engineering that I don't lose that suspension of disbelief. --OuroborosCobra (talk) 20:27, 9 September 2023 (UTC)

So (I suggest), by most definitions of Science Fiction (something that we SF fans have been debating for 90 years or so), Breaking Bad is not SF because it does not seek to use fictional or projected new science to show how this might change the World, but instead tries to portray the World as it actually is (with illegal Meth manufacture) and merely obfusticates some scientific detail so as not to facilitate real criminality. {The poster formerly known as 87.81.230.195} 51.194.81.165 (talk) 07:59, 10 September 2023 (UTC)

I mentioned "science fiction" because someone on a forum back in the day was saying that Walter's method of cooking meth and attaining a high purity (via that specific method - which is real, as far as I'm aware) was an example of such. TBH, I think the show itself lampshades that a little. There's a scene where Walt is chewing/mocking out one of the villain's henchmen who thinks that he can replicate Walt's formula because he's been watching him cook a few times, and pointing out that he really has no idea what the hell he's doing (compares him to a burger flipper, IIRC). Quoth him: "...if our reduction is not stereospecific, then how can our product be enantiomerically pure?". I was really just wondering if there was any actual method of doing this? I'm not asking for details of how to do it, just curious to get an answer to something that has been bugging me since I rewatched. Iloveparrots (talk) 00:28, 11 September 2023 (UTC)

I don't know what reaction Walter claimed to be using but there are many ways to reduce an imine stereospecifically: see Imine#Imine reductions and Hydrogenation of carbon–nitrogen double bonds. The aim would be to give dextromethamphetamine uncontaminated with the less CNS-active levomethamphetamine: "methamphetamine" usually refers to racemic material. Mike Turnbull (talk) 11:43, 11 September 2023 (UTC)