Talk:Archimedes' principle

Incompressible vs compressible fluids

The "Explanation" section says: "the difference between the pressure up against the bottom of the cube and the pressure down against the top of the cube is the same at any depth". I think this is strictly true only if the fluid is incompressible. Perhaps the words "incompressible fluid" should be added to the section whereever appropriate. Jwpat7 (talk) 04:27, 4 September 2012 (UTC)

Why are there two spellings of 'Archimedes' Principle' in the index?

One (Archimedes with an I) leads to this page. The other (Archemedes with a third E) leads to the main page on buoyancy. However that page doesn't use that spelling at all, and has a section labeled 'Archimedes' Principle'. It's just bizarre that a typo redirects to a different page to the page that someone was clearly looking for. 86.181.37.146 (talk) 22:20, 23 March 2014 (UTC)

Fixed. Thanks for finding this. —David Eppstein (talk) 22:58, 23 March 2014 (UTC)

Article Rudimentary / Lacks References

This (scientific) article does not cite references, makes frequent errors (often corrected in parentheticals), uses approximations without clarification (the force of gravity varies on earth and Archimedes' principle applies in space) and is generally poor quality.

Examples:

• "Thus, in short, buoyancy = weight of displaced fluid"
• "the weight of 1 kilogram (technically, as a kilogram is unit of mass and not of force, the buoyant force is the weight of 1 kg, which is approximately 9.8 Newtons.)"
• "10 kilograms (98 newtons)"
• "Objects weigh more in air than they do in water."

As it has the tone of an editor who wrote it from first-hand experience, rather than referenced sources, this article needs a (clean?) revisit.

-Geoff (talk) 07:12, 25 September 2012 (UTC)

A wooden cube in a sphere of water in space.

As Archimedes' principle doesn't depend on surface tension (as mentioned in the article), what will happen if a block of wood is shoved gently into a ball of water in space? Will it 'rise' to the surface? 121.245.112.77 (talk) 05:51, 12 November 2012 (UTC)

If you want to add this to the article (as your recent edits suggest) then you need to find a reliable source stating what happens in this case. Without sources, material such as this becomes original research, which is not allowed on Wikipedia. —David Eppstein (talk) 08:14, 12 November 2012 (UTC)

So now any editing will require it to be published somewhere else first? Huh, ? Is not my statement provable from what is already given? What if I publish this on wordpress/blogger first? What about the Ice melting updates I did? Is that not 'Important' to the article? 121.245.65.89 (talk) 09:20, 12 November 2012 (UTC)

Without either gravity or an accelerating inertial frame, Archimedes' principle does not apply, so the ball of water in space example would be irrelevant. Wordpress and blogger are not WP:Reliable sources. Dbfirs 06:21, 31 May 2018 (UTC)

Insufficient Explanation of the Involved Mechanics

The first sentence of the Formula section makes no sense unless you know that it references a submerged cube. A cube is referenced in the next sentence but even then it is not clear that this cube is completely submerged.

The first paragraph of the Formula section is the only reference to explaining the mechanics of the 'why' of Archimedes' Principle. The 'why' is as important as the observation and should be expanded on considerably. It should also appear in the Explanation section, which currently comprises of more observations and no explantion. A full diagram depicting the varying pressures and forces over the surface of a submerged body would be good.--Quitequick (talk) 08:14, 29 October 2013 (UTC)

Agreed. I came to the talk page to make exactly these points. Mnudelman (talk) 00:13, 27 April 2014 (UTC)

Protection

Can a semi protection be issued for this page because of consistent attacks from an ip account. The same ip has been vandalizing the page for a while now and is "upset we are removing their artwork". InfernusIsHiding-Talk 18:07, 24 September 2014 (UTC)

Shouldn't it be Archimedes's principle ?

English grammar only uses the s' suffix for possessive plurals e.g. all the horses' hooves. When a singular name ends in s the possessive suffix is s's e.g. Jones's principle. Rcbutcher (talk) 08:46, 16 September 2015 (UTC)

Yes, that is correct. Even though it may be commonly pronounced "Archimedes", the actual spelling should be Archimedes's. — ★Parsa ☞ talk 17:41, 10 January 2017 (UTC)

Usage of Archimedes' is common and accepted by several reliable sources, including Encyclopaedia Britannica. The claim that English grammar only uses the s' suffix for plurals is inaccurate. · · · Peter (Southwood) ^(talk): 04:46, 21 December 2017 (UTC)

I prefer the form with final S myself, because it’s thoroughly unambiguous. It’s also generally endorsed by MOS:POSS. But the form without is quite common and widely accepted, especially for polysyllabic Greek, Latin, and biblical names. Some authorities recommend spelling according to one’s pronunciation in these cases, saying that if one wouldn’t pronounce the additional sibilant the final S should be omitted; I expect that fewer people would say “Archimedezəz principle” than e.g. “Charlzəz law”.—Odysseus1479 00:33, 31 May 2018 (UTC)

Are these sentences correct?

"Common demonstrations involve measuring the rise in water level when an object floats on the surface in order to calculate the displaced water. This measurement approach fails with a buoyant submerged object because the rise in the water level is directly related to the volume of the object and not the mass (except if the effective density of the object equals exactly the fluid density). Instead, in the case of submerged buoyant objects, the whole volume of fluid directly above the sample should be considered as the displaced volume. Another common point of confusion regarding Archimedes' principle is that it only applies to submerged objects that are buoyant, not sunk objects. In the case of a sunk object the mass of displaced fluid is less than the mass of the object and the difference is associated with the object's potential energy."

That statement "the whole volume of fluid directly above the sample should be considered as the displaced volume" makes no sense. If you submerge a rigid hollow sphere, the water doesn't rise more if the sphere is 10' deep than if it is 5' deep.

The next statement — "In the case of a sunk object the mass of displaced fluid is less than the mass of the object" — is true, but that is why the object still sinks. The previous sentence, "Archimedes' principle ... only applies to submerged objects that are buoyant, not sunk objects" is wrong. The apparent immersed weight of the denser-than-water object is equal to the mass of the object minus the mass of the displaced water, as shown in the Formula section. 50.185.144.27 (talk) 06:30, 5 March 2017 (UTC)

The whole paragraph is unreferenced, and seems to be someone's opinion. Would anyone object if we remove it? Dbfirs 06:48, 31 May 2018 (UTC)

I changed this. The first part is actually correct (I added a reference to make it more clear). The second part makes no sense. The law is not limited to floating objects.Garnhami (talk) 10:36, 31 May 2018 (UTC)

Thanks for removing the second part and for adding the excellent reference. The only thing is that the explanations in your reference are much clearer than the first part of that paragraph. Dbfirs 12:23, 31 May 2018 (UTC)

you are right. The sentence is still a bit strange. Maybe we need to just use the sentences used on that reference because now it is still very confusing.Garnhami (talk) 12:35, 31 May 2018 (UTC)

“ This measurement approach fails with a buoyant submerged object because the rise in the water level is directly related to the volume of the object and not the mass (except if the effective density of the object equals exactly the fluid density).“ Is there a specific passage in support of the statement? 188.149.62.60 (talk) 19:48, 26 May 2020 (UTC)

Displacement

The statement of the principle, whilst very common, is not completely correct.

In general, the idea that a certain volume of fluid must be displaced is not correct. An indefinitely large body (with density less than the fluid) can float in an indefinitely small volume of liquid, provided the body is confined sufficiently closely by the container. Imagine a pencil that almost fills a test tube. Only a small amount of water is needed to make it float. A body floating on water weighs exactly as much as the water whose place it occupies – not displaces. This is because the level of water rises as the body descends into it.

A correct statement of the principle of Archimedes is: any body completely or partially submerged in a fluid at rest is acted upon by an upward, or buoyant, force, the magnitude of which is equal to the weight of a volume of fluid equal to that of the submerged portion of the body.

Based on Chalmers, A.F. (2017) One Hundred Years of Pressure: Hydrostatics from Stevin to Newton. Archimedes, Springer, Cham, Switzerland, vol. 51. --Jonathan Webley (talk) 15:56, 26 July 2018 (UTC)

Potentially misleading wording

In the Explanation section, the article says the following: "If this net force is positive, the object rises; if negative, the object sinks; and if zero, the object is neutrally buoyant—that is, it remains in place without either rising or sinking." In its current wording, this could be taken to mean that whether the object moves upwards, downwards or stays level is determined solely by the net force on it. The issue is that the net force determines the acceleration, rather than the velocity, of the object. While this is unlikely to confuse most people, the wording does seem to line up with a pre-Newtonian understanding of motion, so would it be worth adjusting the wording, for the sake of accuracy? Alex the weeb (talk) 11:07, 16 April 2021 (UTC)

Formula section and examples, etc.

This edit caught my eye, and caused me to look at the examples. Those have been around since this 2011 edit. Am I just especially dense this morning or does the second example about the helium balloon in an automobile undergoing lateral acceleration while going around a curve seem to other editors to be less than helpful in the understanding of the formulas which are the topic of this section? For that matter, I had to look at the prose in the section a couple of times before it started making sense to me. If it's not just me, hopefully some other editor who is better at basic physics and at writing article prose than I will try to improve this section on formulas related to Archimedes' principle.

While I was looking at this, I made a bold edit here, relocating a figure and tweaking the caption. I notice that, though F_a in the image caption appears in the section to which I've moved the image, F_b doesn't appear until a later section. Perhaps some other editor can tie things together better here. Wtmitchell (talk) (earlier Boracay Bill) 11:00, 7 January 2022 (UTC)

Semi-protected edit request on 6 April 2023

It should be "equal to the object's MASS" not weight! 2001:1970:549C:F800:6F6F:F6E0:4360:A95F (talk) 23:43, 6 April 2023 (UTC)

 Not done: It actually is the weight. Consider an object floating on the surface of a fluid - the weight is the force pushing it down into the fluid. As the object is floating, not rising into the air or sinking into the fluid, the buoyant force must exactly equal the downward force generated by the object's weight. If gravity suddenly decreased to near-zero, the object would retain the same mass, but that does not mean the buoyant force would as well (if it did, the object would go flying into the air). Tollens (talk) 04:12, 7 April 2023 (UTC)