Talk:Neutral buoyancy

External forces

Buoyancy is only concerned with the balance of upthrust and downthrust. A submarine increasing its speed or changing its velocity as it turns can still be trimmed for neutral buoyancy, yet the sum of external forces acting on it is clearly not zero. I've therefore reverted yet again the incorrect changes by User:Ghnatiuk, which they have added four times now. See the page history, specifically these diffs: [1], [2], [3], [4]. --RexxS (talk) 17:49, 2 December 2018 (UTC)

Hello, It has taken some time for me to figure out how to communicate and use these pages. I am new to this and did not find it at all user friendly to navigate. I did not intend to disrupt the page or discussion. My apologies.

There is good reason to state in the opening description of neutral buoyancy about the balance of forces in the direction of the applied gravitational force so one understands that gravity plays an important role in this and it is not just all about densities. Without gravity creating a pressure gradient in the medium as a function of distance from the gravitational source, there would be no buoyancy. Being a scuba diver, I understand your bias toward emphasizing density.

I should have been more specific for I had in mind the "upthrust" and "downthrust" when I stated the sum of external forces to be zero (along the gravitational force field lines) and was not considering lateral forces as part of the force balance equation. In that respect you are correct in also considering the possibility of lateral forces for which buoyancy plays no part.

I have been trying to come up with a way to word this to emphasize that neutral buoyancy is due to a balance of forces along the direction of gravity which results from the equal average density condition. Something like this:

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Neutral buoyancy is the condition of a physical body which when immersed in a medium the buoyant force is equal to the gravitational force. This condition is satisfied when the average density of the physical body is equal to the density of the medium.

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The reviewers might think about taking this into consideration before making an final decisions regarding the topic. Buoyancy has to do with balancing forces (not densities) which is a consequence of Newton's first law of motion. Thank you for your time and again my apologies for not figuring out how to use these talk pages earlier.

George Hnatiuk — Preceding unsigned comment added by Ghnatiuk (talk • contribs) 20:07, 2 December 2018 (UTC)

@Ghnatiuk: Please don't put your personal information on Wikipedia pages (unless you want your email mercilessly spammed).

There are no "reviewers"; it's just you and me and whoever else wants to chime in. And there's no "final decision"; each consensus on wording lasts just until it changes.

Also, I was a physicist long before I was a scuba diver, so you may be better off not jumping to any conclusions about my biases.

I do understand that neutral buoyancy results from a balance between down-force and up-force on a body immersed in a fluid – in normal experience, that means weight is balanced by buoyant upthrust. However, in practical terms, we actually trim the either the body's mass (e.g. a submarine) or volume (e.g. a diver) in order to match the forces. We don't directly alter the force on a body to achieve neutral buoyancy; we manipulate its density. It's just as true to say that the matching of forces results from matching the densities as it is to say that matching the densities is a consequence of matching the forces. If anything, I think you'll find the former formulation is easier for the lay reader to grasp, since density is more of a concrete concept than force.

Please understand that the lead (the first part) of the article is written as a simplified overview and is meant to be accessible to a broad range of readership – I believe "density" is more within the experience of more readers than "force".

The article is not devoid of mention of force, as the second sentence currently mentions the force of gravity:

• The buoyancy offsets the force of gravity that would otherwise cause the object to sink ...

In addition, the link to Buoyancy takes the reader to an article that goes into considerable depth on the forces acting on a submersed body, deriving the buoyant force by integrating the stress tensor over the surface of the body which is in contact with the fluid.

Personally. I would prefer an opening sentence along the lines of:

• Neutral buoyancy occurs when a body's average density is equal to the density of the fluid in which it is immersed.

I don't see any point in calling it a "condition", nor does the possibility of a non-physical body seem likely, so that "physical body" is redundant. I would criticise your formulation for the use of "medium", an ambiguous and broad term for most readers, compared with the absolutely precise word "fluid". Although I admit that many readers may not grasp that "fluid" includes gases.

I concede that the lead would benefit from some emphasis on the fact that the forces of upthrust and weight are balanced. Perhaps the second sentence should begin:

• The buoyant force offsets the force of gravity that would otherwise cause the object to sink ...

with the link to the Buoyancy article being made as early as possible.

Hopefully, other editors will join in this discussion and give further opinions. --RexxS (talk) 23:06, 2 December 2018 (UTC)

RexxS, I do not disagree with anything you stated. The use of "condition" and "physical body" were from the original post for I tried to use it's wording as much as possible though I do not like to reference this as a condition either. Fluid is fine instead of medium but many people as you pointed out misconstrue fluid in this situation as not also encompassing gases which is further complicated by the scuba diver example in water. Many will not see the equivalence of say a helium filled balloon "floating" in the atmosphere with a counter weight. Finding wording that is concise yet general is indeed an art form in itself and very difficult. My original posting was indeed cumbersome and wordy. Being technical by training (engineer and mathematician) I sometimes get caught up in trying to be too detailed and want to cover all bases. Fluid instead of medium is fine or maybe saying: Neutral buoyancy occurs when a body's average density is equal to the density of the fluid/gas in which it is immersed. Either way is OK. Instead of "body" maybe a more general term such as "object" would be more appropriate.

I do agree with you on the reference to buoyancy early on is prudent with a hyperlink to the Buoyancy article. Following this by the use of "buoyant force" helps drive home the equivalence of the terms "buoyancy" and "buoyant force".

How about something like this:

Neutral buoyancy occurs when a body's average density is equal to the density of the fluid in which it is immersed resulting in the buoyant force offsetting the force of gravity that would otherwise cause the object to sink ...

OR

Neutral buoyancy occurs when a object's average density is equal to the density of the fluid/gas in which it is immersed resulting in the buoyant force offsetting the force of gravity that would otherwise cause the object to sink ...

Something to that effect to somehow sneak "force" into the first lead in sentence along with the density.

Now let me relate why, in my opinion, this is important. Recently I have come across groups of non-technical individuals that read the first sentence of the wiki neutral buoyancy page and stop there not to read further into the 2nd sentence and beyond to see the connection density has to forces and gravity in the buoyancy phenomena. They feel everything we observe regarding the motional behavior of objects in water and the atmosphere can be explained by density alone without considering the concept of gravity. There are "flat earthers" and "gravity deniers" alike that have used this wiki page to justify their position because it only mentions density in the lead in sentence - no forces needed to explain buoyancy, no gravity etc. I know that is ridiculous and hard to believe but that is the situation hence my motivation to have the lead in modified to include forces. Petty it is I know, but these are very non-technical people and they do not know how to read the pages beyond the first sentence to obtain a more in depth understanding of the connection between buoyancy, gravity and the balance of forces. Until this recently occurred, I never was concerned with the neutral buoyancy page for the second sentence introduced the connection of forces to the neutral buoyancy. Should we be concerned with what gravity deniers think? Probably not but a minor "tweek" of the page could remedy the stupidity that these people employ to use the wiki page to support their world view.

To see what I am getting at, watch 2 minutes of this show I came across today originating out of the UK. Begin listening at time 1:07:30 https://www.youtube.com/watch?v=VoR52F-ygeQ

In light of this, use your best judgement and I will go with it.

Regards, George Hnatiuk — Preceding unsigned comment added by Ghnatiuk (talk • contribs) 02:35, 3 December 2018 (UTC)

@Ghnatiuk: I understand the problem you're describing. Although I'd rather keep sentences brief in the lead, perhaps it would be better to adopt your suggestion. Would you be content with this:

• Neutral buoyancy occurs when a object's average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink ...

I think "balancing" is easier to comprehend than "offset", and the "/" is a construction to avoid. It's probably a good idea to explain that a gas is also a fluid somewhere later in the article - perhaps an example related to a hot-air balloon? --RexxS (talk) 19:22, 3 December 2018 (UTC)

@RexxS: Good afternoon sir,

I like it. That is a good compromise - short and to the point. Thank you for taking my concerns under advisement. There are truly many nut cases out there and for them to deny good physics and in the process use the wiki pages to misconstrue explanations and meanings is reprehensible. Thanks again, George Hnatiuk

PS again my apology for the rough start and initial disruption. I am a newbie to communicating on wiki and it took awhile to figure out the protocol. — Preceding unsigned comment added by 140.186.248.154 (talk) 20:15, 3 December 2018 (UTC)

@Ghnatiuk: I've now amended the opening sentence as agreed, and added a hot-air balloon example to Neutral buoyancy #Uses. Perhaps you would be kind enough to look over the second addition and adjust it if you feel I've not got it right. --RexxS (talk) 15:44, 4 December 2018 (UTC)

@RexxS: The Eagle has landed. Good job. I like it very much. Short and to the point - well written. With cooperation we were able to find just the right set of verbs and adjectives to convey the information. Thank you for working with me on this in spite of the rough beginning. I also like what you did with the hot air balloon - I see no need for modification - leave it as you have written it.

Just one final suggestion. In the section at the bottom where you have common densities. Maybe list the ice with a bit more precision as 0.917g/cm^3 or 0.9168g/cm^3 rather than 0.92 at 0 deg. C seeing how important that substance is here on earth. It would save someone wishing to make a calculation with greater precision from having to search further -- kind of like one stop shopping on this page.

Thanks and possibly we will have a chance to work together again in the future -- have yourself a good upcoming holiday. George Hnatiuk