Wikipedia:Reference desk/Archives/Science/2021 December 2
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December 2
[edit]Without buoyancy, are raindrops becomes heavy than normal?
[edit]Without buoyancy , are raindrops becomes heavy than normal? Rizosome (talk) 09:08, 2 December 2021 (UTC)
- No. Buoyancy does not affect the mass (or weight) of anything.--Shantavira|feed me 11:36, 2 December 2021 (UTC)
- It is not uncommon to find statements in popular science texts such as, "A crown weighs less when immersed in water than it weighs in air."[1] But this is not correct when using the scientific definition of weight, which is purely the force due to gravity. It would be correct to say that it feels less heavy. Weight cannot be measured directly. What can be measured is the force of reaction needed to keep a body stationary while it is subject to an action force. That is what a weighing scale does. The action force on a body immersed in a liquid is the force of gravity minus the buoyancy. If the density of the liquid is very small compared to that of the body, it may be ignored – as is usual for a person (with a density about 800 times that of air) stepping on a scale that is not very precise anyway. --Lambiam 12:28, 2 December 2021 (UTC)
- "Weight" is actually inconsistently defined. There have been some people who insist (but it turns out, very few actually use in practice) the "weight = force of gravity" definition, even as it turns out, actual practicing physicists. You've just implied three different definitions of weight (weight as synonym of mass, weight as force of gravity, weight as "force of reaction" (i.e. normal force) on a scale). All three get used in different contexts, often without elaboration as to which the speaker means. We even invented the concept of "mass" to avoid these differences in definition, but it turns out even that has problems; inertial mass and gravitational mass were tantalizingly the same thing every time we measured them, but no one could come up with a way to prove they were the same thing until general relativity. The real issue is that when we try to create precise, unambiguous definitions, we run into the two distinct problems of language and measurement. Language is fundamentally ambiguous; there is no natural human communication system which is capable of perfect precision, and that includes scientific nomenclature. And regardless of how you define something like "weight", the most precise definition suffers from a lack of reasonable physical means to actually measure it, which means that as it becomes more precise, it becomes less useful. For example, if we want to accept that weight is the force of gravity alone, ignoring all other forces, then how can you devise a practical scale to measure that? You can only actually measure the normal force using such a scale, and the normal force is approximately the force of gravity, but never the force of gravity alone. --Jayron32 13:30, 2 December 2021 (UTC)
- From our archives:
- To throw some fuel on this fire - are astronauts on the International Space Station subject to "zero gravity," "microgravity," or "almost the same amount of gravity as someone on the Earth's surface"? I think the answer depends on whether you're discussing the topic with schoolchildren, ...with their teachers, or with spacecraft design engineers. Pilots and astronauts, being very task-saturated during calculation of their G forces, say they get to zero-G here on Earth, presumably due to the buoyant force of phlogistan that ebbs and flows in This New Ocean. Nimur (talk) 17:54, 2 December 2021 (UTC)
- "Weight" is actually inconsistently defined. There have been some people who insist (but it turns out, very few actually use in practice) the "weight = force of gravity" definition, even as it turns out, actual practicing physicists. You've just implied three different definitions of weight (weight as synonym of mass, weight as force of gravity, weight as "force of reaction" (i.e. normal force) on a scale). All three get used in different contexts, often without elaboration as to which the speaker means. We even invented the concept of "mass" to avoid these differences in definition, but it turns out even that has problems; inertial mass and gravitational mass were tantalizingly the same thing every time we measured them, but no one could come up with a way to prove they were the same thing until general relativity. The real issue is that when we try to create precise, unambiguous definitions, we run into the two distinct problems of language and measurement. Language is fundamentally ambiguous; there is no natural human communication system which is capable of perfect precision, and that includes scientific nomenclature. And regardless of how you define something like "weight", the most precise definition suffers from a lack of reasonable physical means to actually measure it, which means that as it becomes more precise, it becomes less useful. For example, if we want to accept that weight is the force of gravity alone, ignoring all other forces, then how can you devise a practical scale to measure that? You can only actually measure the normal force using such a scale, and the normal force is approximately the force of gravity, but never the force of gravity alone. --Jayron32 13:30, 2 December 2021 (UTC)
- The concept of weight can be divided into apparent weight and actual weight, also called true weight. The former takes buoyancy into account. A piece of wood under water or a helium balloon in air even have negative apparent weights. If you immerse a scale in a swimming pool and weigh yourself you'll find the scale measures apparent weight (unless you have a scale with an unusually convoluted mechanism). 85.76.71.10 (talk) 14:57, 2 December 2021 (UTC)
- You can do all kinds of things. It's just refinements on top of refinements on top of refinements, and again, precision and usefulness work at cross purposes here. One more thing worth mentioning is that, one of the other main problems with the re-definition of weight as "the force of gravity" is that such a definition was basically created out of thin air for no real reason, it seems. We already have a perfectly usable term for the force of gravity. It's called "the force of gravity". It works great, there's no reason to appropriate another word and make it a synonym for the force of gravity if you just mean the force of gravity anyways. Weight as a concept is a far older thing than is mass, and it didn't mean the force of gravity, it meant "how heavy is this thing" and you measured how heavy it was by putting it on a scale. It's a perfectly good functional word for that purpose, and we do a disservice to all when we insist that it now means "the force of gravity and nothing else", especially when the term "the force of gravity" already means that. See here, the sense of weight as a measure of heaviness dates to Old English. There was no good reason to insist that it meant something else once we tried to separate the meaning from "mass", which in the sense of "that thing we measure in grams" only dates from 1704. --Jayron32 15:08, 2 December 2021 (UTC)
- It is not uncommon to find statements in popular science texts such as, "A crown weighs less when immersed in water than it weighs in air."[1] But this is not correct when using the scientific definition of weight, which is purely the force due to gravity. It would be correct to say that it feels less heavy. Weight cannot be measured directly. What can be measured is the force of reaction needed to keep a body stationary while it is subject to an action force. That is what a weighing scale does. The action force on a body immersed in a liquid is the force of gravity minus the buoyancy. If the density of the liquid is very small compared to that of the body, it may be ignored – as is usual for a person (with a density about 800 times that of air) stepping on a scale that is not very precise anyway. --Lambiam 12:28, 2 December 2021 (UTC)
- A raindrop feels 0.1% heavier in hydrogen but the mass stays the same. Sagittarian Milky Way (talk) 15:17, 2 December 2021 (UTC)
@Shantavira: If Buoyancy does not affect the mass (or weight) of anything. Then, how ship won't sink in water or ice berg won't sink in water? Rizosome (talk) 01:41, 3 December 2021 (UTC)
- Whether a heavy ship or other body will sink depends on its apparent weight, which is its actual weight (its mass multiplied by the local gravitational acceleration) minus the buoyancy (which its the weight of the displaced water – see Archimedes' principle). For a ship floating in water these two forces have equal magnitude and so they cancel each other: the ship has an apparent weight of 0 N. That the ship is actually still quite heavy becomes apparent when you try to lift it out of the water. That it has considerable mass is apparent when you try to halt the moving ship, merely coasting after its motors stopped. --Lambiam 06:18, 3 December 2021 (UTC)
- And the iceberg floats because ice is less dense than water. TigraanClick here for my talk page ("private" contact) 08:32, 3 December 2021 (UTC)
I still don't understand the original question. What does any of this have to do with raindrops?--Shantavira|feed me 10:43, 3 December 2021 (UTC)
- The original question asked about heaviness, an imprecise term, that can refer to either density, mass, or weight depending on context. Terms like mass and weight are also themselves imprecise terms, and the follow-on discussion was about teasing out those complexities. Without the buoyant force of air, raindrops (and everything else) would drop faster. The OP, however, asked if they would be heavier, which because such a term has multiple meanings, depends on what one means by "heavy". --Jayron32 11:52, 3 December 2021 (UTC)
Due to complexity involved, I considered it my question as open question in physics world : Terms like mass and weight are also themselves imprecise terms, and the follow-on discussion was about teasing out those complexities. Rizosome (talk) 02:03, 4 December 2021 (UTC)
ResolvedWhy is a single paper about fossil turtles cited with dates 2016 sometimes and 2017 other times?
[edit]My question concerns this article. Clearly, from the article information, it was published in 2016, and its title is "A new turtle taxon (Podocnemidoidea, Bothremydidae) reveals the oldest known dispersal event of the crown Pleurodira from Gondwana to Laurasia." Zoobank, for example, cites it with the 2016 date and describes the new species as "Algorachelus peregrinus Pérez-García, 2016."
But several others, including Pérez-García himself in 2020, cite this paper with a 2017 date: "Pérez-García, A. (2017b). A new turtle taxon (Podocnemidoidea, Bothremydidae) reveals the oldest known dispersal event of the crown Pleurodira from Gondwana to Laurasia. Journal of Systematic Palaeontology, 15, 709–731."
Why are both dates used, and which should I use when citing it in Wikipedia articles? HouseOfChange (talk) 18:12, 2 December 2021 (UTC)
- The page says the paper was published online 28 Sep 2016, but if you look at the top right it was printed in volume 15 of the journal, which was for 2017. A paper can be published online almost immediately after it was accepted whereas printing it requires quite a bit of time. I would always cite the printed version with the cover date of the journal issue, in this case 2017. --Wrongfilter (talk) 18:28, 2 December 2021 (UTC)
- ... in case a Malthusian extinction should ever eliminate all digital archives, but the rampaging horde chooses not to burn the vaults full of paper print zoology journals? I wonder, realistically, which archival-format will last longer...
- Wikipedia:Manual of Style links to citation style, which advises: "say where you read it." Unless you actually referenced a print copy of the 2017 publication, you ought to cite the digital copy, and its digital publication date, I think. Without independent verification, can you be sure that the printed publication is really the same article, as opposed to a "pretty similar one" with a "pretty similar title"? Nimur (talk) 20:15, 2 December 2021 (UTC)
- If it's the web site of a respectable journal, if a pdf version of the paper is available, if it includes the full journal reference with volume number, page number or article id and publication year, then in all likelihood that is the definitive version. If it isn't then something is very wrong. In this case you can download the citation, you'll find that it gives 2017. And no, I don't cite anything that I haven't seen. --Wrongfilter (talk) 22:13, 2 December 2021 (UTC)
- This is a thorny issue: have a look here. The data of publication is particularly important for the formal descriptions of new species, because the first published name has priority and because the full name of the species includes the date of publication. For old works, the critical issue is to try to establish when the work was actually sent out to libraries (rather than printed), hence the importance of library stamps on the covers of old journals that establish when that issue arrived. For modern journals published online and then printed it is critical to establish whether online-first versions are the version of record or if they may later be altered in non-trivial ways (i.e. not just a change of page numbering). "Version of record" is better explained here than in the Wikipedia article. Jmchutchinson (talk) 21:46, 2 December 2021 (UTC)