Wikipedia:Reference desk/Archives/Science/2023 December 12

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December 12

How old is a molecule of water

If you have some water, how old are the molecules, typically? Bubba73 ^{You talkin' to me?} 04:30, 12 December 2023 (UTC)

Same age as the earth, one would think? 67.169.17.27 (talk) 04:31, 12 December 2023 (UTC)

Not necessarily. According to "Origin of water on Earth" it may have been formed on Earth after the Earth's formation, or it may have come from somewhere other than Earth. Mitch Ames (talk) 04:53, 12 December 2023 (UTC)

Ceccarelli, Cecillia; Du, Fujun (June 2022). "We Drink Good 4.5-Billion-Year-Old Water" (PDF). Elements. 18 (3). doi:10.2138/gselements.18.3.155.

Given water is produced by many chemical reactions and destroyed by many chemical reactions, that IP's answer is obviously very wrong. And even if you have a bucket of water that is not being produced or destroyed by other reactions, water is a chemically dynamic environment, not static independent molecules that happen to be near each other. The specific H₂O molecules themselves have a finite lifetime, due to the self-ionization of water and general proton-transfer in the hydrogen bonded network. The former article notes "Random fluctuations in molecular motions occasionally (about once every 10 hours per water molecule) produce an electric field strong enough to break an oxygen–hydrogen bond, resulting in a hydroxide (OH−) and hydronium ion (H3O+); the hydrogen nucleus of the hydronium ion travels along water molecules by the Grotthuss mechanism and a change in the hydrogen bond network in the solvent isolates the two ions, which are stabilized by solvation. Within 1 picosecond, however, a second reorganization of the hydrogen bond network allows rapid proton transfer down the electric potential difference and subsequent recombination of the ions..." (refs and links omitted). So dissociation/association is fast, and happens often. I don't have the actual reaction-rate data at hand, but if one mixes ²H₂O with regular water (mostly ¹H₂O), one quickly gets ²H¹HO, demonstrating that any given water molecule does not retain its specifc two hydrogen atoms and one oxygen atom composition for very long. DMacks (talk) 05:02, 12 December 2023 (UTC)

@DMacks, I love your answer, but I do have one question. How much of this would apply to frozen water, such as permafrost or glaciers? I would personally doubt that self-ionization is much of an issue under those circumstances, so perhaps "older water molecules" could be found there? I'm not sure if quantum tunneling of water would be an issue, though. Of course, since one molecule of light water is physically identical in basically every way to another molecule of light water, the question itself is has no real physical relevance beyond being a fun thought experiment. --OuroborosCobra (talk) 16:31, 19 December 2023 (UTC)

Railroad question

How fast could an EMD E-unit go on one engine (assuming straight, level track, no speed restrictions and a train of typical size and weight for post-Great Depression, pre-World War 2 express trains)? 67.169.17.27 (talk) 04:37, 12 December 2023 (UTC)

It was normal to use multiple locomotives to haul a single express train, but let's assume this train is short enough that a single locomotive can bring it to its normal top speed. Each locomotive had two identical diesel engines. Running on one engine, power is halved. On level track, the engine works mostly against air drag, and power increases with the cube of speed. Half power means that speed is cut by 21%. With diesel-electric transmission, there shouldn't be a significant effect on efficiency.

Half the power also means half the climbing speed and half the acceleration, so the cut in average speed is worse than the cut in top speed. PiusImpavidus (talk) 14:07, 12 December 2023 (UTC)

In 1937 when EMD E-units were entering service they could be compared with the German DRG Class SVT 137 streamlined diesel that had a regular maximum speed of 160 km/h (99 mph) and had reached a world speed record of 205 km/h (127 mph). Philvoids (talk) 14:10, 12 December 2023 (UTC)

That must be the record for regular production trains. The absolute record was already faster and held by an experimental German railcar. PiusImpavidus (talk) 17:09, 13 December 2023 (UTC)

Yes, but there's a qualitative difference between a locomotive designed and used to haul trains, and a self-contained railcar that was not intended to haul anything, and because of its design could not effectively do so even in principle. {The poster formerly known as 87.81.23-0.195} 90.199.215.44 (talk) 01:36, 14 December 2023 (UTC)

You're quite right that the Schienenzeppelin wasn't scalable and therefore a technological dead end. At best, it could be used for research or VIP runs. But you don't need a locomotive to run useful fast trains. The DRG Class SVT 137 was no locomotive, but, like most fast trains, both now and back in the 1930s, a multiple-unit trainset. The experimental three-phase railcar of 1903 (210 km/h (130 mph), also German) was scalable. Its current collection method just wasn't very practical. PiusImpavidus (talk) 14:38, 14 December 2023 (UTC)

From the EA and EB models built 1937–8 to the E9s built 1954–64, the E-units had 5 successively more powerful models of Prime movers (engines), whose maximum power outputs (in pairs) rose from 1,800 to 2,400 hp. The answer will in part depend on which engines are in question, though there are likely other factors, such as the Traction motors used on given models (about which the article is largely silent, but which may not have been altered from model to model) and other equipment variations such as gear ratios, which this site discusses. {The poster formerly known as 87.81.230.195} 90.199.215.44 (talk) 14:21, 12 December 2023 (UTC)

Combining this all gives an estimate for the maximum speed of ³√1⁄2 × (2400/1800) × 160 km/h ≈ 140 km/h, or, using the earlier speed record of 205 km/h, a top speed of about 180 km/h.  --Lambiam 19:08, 12 December 2023 (UTC)

A pre-WW2 express train (as specified in the question) would have had one of the earlier models of the E-unit, but yes, a top speed of about 140 km/h (87 mph) sounds about right. Considering that the Pioneer Zephyr (of the same period) on its famous run in 1934 reached a top speed of 112.5 mph (181.1 km/h), although it was mostly noted for its high average speed (1,015.4 miles (1,634.1 km) from Denver to Chicago in 13:04:58 hours, giving an average of 77.61 mph (124.90 km/h)). PiusImpavidus (talk) 17:09, 13 December 2023 (UTC)

Thanks! I was guessing about 80-90, so that's pretty much what I figured! 2601:646:8080:FC40:3503:6143:E40E:14BD (talk) 04:05, 16 December 2023 (UTC)

UK metric system

Why the metric system did not spread to the United Kingdom as quickly as the other France's neighboring countries? So, why UK does not have long history of metrication? --40bus (talk) 20:19, 12 December 2023 (UTC)

Please, see Metrication in the United Kingdom. Ruslik_Zero 20:37, 12 December 2023 (UTC)

Very simply and briefly: Napoleon Bonaparte. A large part of western Europe came under the control (directly or indirectly) of France during Napoleon's reign and accepted what they were told. The British were at war with France during this period and were unlikely to adopt anything which had a whiff of Napoleon or France about it. Indeed I can recall the phrase "Napoleonic or Christian units" being used humorously in model engineering circles (c. 1990) to refer to metric or imperial. Martin of Sheffield (talk) 22:48, 12 December 2023 (UTC)

"[They] accepted what they were told" sounds as if they had a choice.  --Lambiam 07:58, 13 December 2023 (UTC)

Similar to comedian Larry Miller, talking about a pub crawl: "We decided to leave, right after we were thrown out." ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:29, 16 December 2023 (UTC)

There was a choice. When Napoleon had left, the Dutch chose to revert to their old units, but very soon thereafter returned to metric, because it was simply better.

Thing is, the UK had been one country for a while, under one king, and had been able to standardise its units all over the island already a long time before. The continent didn't have any such central rule, so there were borders everywhere where the units changed, but nobody had the power to select one standard over another. Until Napoleon. PiusImpavidus (talk) 17:17, 13 December 2023 (UTC)

So, if I understand this correctly, the Dutch explicitly rejected what they had been told as soon as they had a choice, and later accepted the new standard, not because they had been told to, but because they deemed it better, perhaps more for mercantile reasons than for any other reason.  --Lambiam 15:20, 14 December 2023 (UTC)

Yes, the metric system was introduced in the Netherlands in 1795 (not really imposed; the Dutch had their own revolutionary government, at that point still somewhat independent of the French), abolished in 1814 because it was French and everything French was bad, and reintroduced as the only legal system in 1820. The French names of the units were still bad, so the traditional Dutch names were used, but now defined as the metric units. PiusImpavidus (talk) 16:38, 14 December 2023 (UTC)

Yes, the Système International has its roots in the French Revolution, of which we Britons did not approve (to put it mildly). We also failed to adopt decimal time and the French Republican calendar, and it took us until 1971 to decimalise our currency of pounds, shillings and pence. Give us time, we'll get there eventually. Alansplodge (talk) 17:23, 13 December 2023 (UTC)

"Give us time" - yes. We started to decimalise the currency in 1849 with the introduction of the florin. 122 years seems about right. It always seemed a bit odd as a lad that we had the two bob bit and the half crown, so similar in value and size. Martin of Sheffield (talk) 17:47, 13 December 2023 (UTC)

"Better" is not necessarily a fact. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:22, 13 December 2023 (UTC)

Not only the pounds, inches and feet changed every 30 km, even the number of inches in a foot was variable, and the variations were well over 10%. And 11 (as in, 11 inches per foot) isn't a very convenient conversion factor. So many people (including the king) considered the metric system better. PiusImpavidus (talk) 16:17, 14 December 2023 (UTC)

That must be why they still use miles and miles-per-hour. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:47, 14 December 2023 (UTC)

I believe PiusImpavidus was talking about the Netherlands. In the UK, there were some variations in units used locally or in different trades, but the system was unified by the Weights and Measures Act 1825 and fine-tuned by several Weights and Measures Acts in the following decades. I think our lingering use of a few Imperial measures such as mph is due to a lack of courage by politicians, nobody wants to be the subject of the outcry which would invariably follow. Maybe George Orwell had a hand in this; in Nineteen Eighty-Four, enforced metrication (specifically of beer measures) is equated with totalitarian rule. Alansplodge (talk) 11:11, 15 December 2023 (UTC)

He had a point! ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:23, 16 December 2023 (UTC)

PiusImpavidus said: "Thing is, the UK had been one country for a while, under one king, and had been able to standardise its units all over the island already a long time before." Hmm. Read the Second Report of the Commissioners for Weights and Measures (1820), published five years after the battle of Waterloo, and reconsider. For example, there are 12 definitions of the hundredweight, around 20 English and 16 Scottish definitions of the pound (mass), and over two pages of bushels. Even the Scottish inch and foot are different to tthe English ones. So, no, not really. MinorProphet (talk) 00:41, 14 December 2023 (UTC)

A lot of local, special purpose units of volume and mass, but at least the avoirdupois (or was it troy?) pounds and ounces appear to have been an official standard all over the UK, along with inches and most derived units of length. The difference between English and Scottish inches was too small to matter for most practical purposes and presumably the result of a copying error. It looks like a better situation than on the continent before metrication. PiusImpavidus (talk) 16:07, 14 December 2023 (UTC)

How much of British trade was with Europe vs how much was with their own empire (which would have used British units)? If 80% of imports and exports was in the same units as domestic trade, why would they bother changing? --User:Khajidha (talk) (contributions) 14:03, 14 December 2023 (UTC)

The history of weights and measures is a subject which only the certifiably insane should tackle. If you really want to boggle your mind, investigate History of measurement systems in India and Indian units of measurement (the greater part of the Empire), and consider that the Troy pound was the standard legal weight in Britain and its colonies (along with the yard and gallon) from 1826 to 1856, although the prototype pound was destroyed in the disastrous fire in the Houses of Parliament in 1834. For British trade in the 19th century, see Pax Britannica for starters. MinorProphet (talk) 15:05, 14 December 2023 (UTC)

It's not just the UK in Europe who have been dragging their Metric feet (excuse the pun), see Metrication in Sweden:

Giving the measurements [for timber] in inches was still common in the late 20th century, about 100 years after the metric system was implemented. Alansplodge (talk) 17:32, 15 December 2023 (UTC)

It's still common - at least Down Here - for newborn babies' weights and heights (?lengths) to be given in pounds/ounces, and inches, even though none of the mothers giving birth nowadays have ever lived under the Imperial system. -- Jack of Oz ^{[pleasantries]} 20:23, 15 December 2023 (UTC)

I believe that Australian hospitals stopped giving babies' weights in pounds and ounces some years ago, but grandmothers have maintained the tradition. HiLo48 (talk) 04:48, 16 December 2023 (UTC)

Here in the UK I have in front of me a 454g jar of honey, and a 907g tin of golden syrup. I am shocked, shocked I say, at any suggestion that Britain is not fully metrificated! -- Verbarson  ^talk_edits 21:07, 15 December 2023 (UTC)

Suspiciously specific, as in 1 and 2 pound jars, yes? :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:23, 16 December 2023 (UTC)

Couldn't say. There are no imperial measurements marked on either container, so I can maintain my plausible shockability. -- Verbarson  ^talk_edits 10:17, 16 December 2023 (UTC)

Don't forget the estimated sign ℮, meaning that the containers' contents will be 440–468 g (15+1⁄2 oz – 1 lb 1⁄2 oz) and 892–922 g (1 lb 15+7⁄16 oz – 2 lb 1⁄2 oz) respectively (or thereabouts). Bazza (talk) 10:38, 16 December 2023 (UTC)

Ah yes, European short measure pint beer bottles (500ml vs 1pt), European short measure loose foodstuffs (100g vs 4oz) and to cap it all we don't even get full measure with the ℮-cheat. Bah-humbug! :-) Martin of Sheffield (talk) 10:56, 16 December 2023 (UTC)

Anyone who describes 500 ml as "a pint" on their container is obviously wrong, but I would imagine manufacturers don't do that. This is why Imperial measures have survived - they are convenient. The half crown was discontinued from 1851 but was brought back by popular demand in 1874. In my supermarket you can ask for "a quarter" of something and get it (a notice tells you its equivalent in grammes and the appropriate quantity is weighed out on the metric scale). 2A02:C7B:103:7100:D984:512D:2947:50AE (talk) 12:12, 16 December 2023 (UTC)

Just waiting for JackofOz to enlighten us about Adelaide pints. Bazza (talk) 13:24, 16 December 2023 (UTC)

I'm afraid the plethora of Aussie beer glass naming conventions is as much a mystery to me as anyone else. I couldn't even tell you how it's done in my own state of Victoria. My pub days are a distant memory (they date from my post-teenage years in Queensland, and then I spent 25+ years in Canberra before moving south). -- Jack of Oz ^{[pleasantries]} 20:43, 16 December 2023 (UTC)

I think most of Europe uses the inch for TV screens. In the 80s of last century you could still ask for butter by the demi-livre in France. You'd get 250 grammes, which isn't far out. DuncanHill (talk) 21:17, 16 December 2023 (UTC)

Since they introduced the horsepower, you know... and look at this one! Could be used without a cord (do not know about the network it doesn't apply much to TV screens) -- Grand-Pressigny, farmers collecting them used to call them "livre de beurre" at least the same kind of nearness is to be found in relationship with capacity, so: the Demiard --Askedonty (talk) 19:50, 18 December 2023 (UTC)