Talk:Buoyancy

SI units

Changed the example's units from pounds to Newtons to maintain the use of SI on Wikipedia.

It is conventional in English to write "3 pounds of water" when one means a quantity of water that weighs 3 pounds. But does one follow that usage with Newtons? Michael Hardy 21:48, 12 Apr 2005 (UTC)

Newtons are a unit of force and therefore are a unit of weight, I believe. I'm sure it's correct, but whether or not it's commonly accepted is a bit dubious.--Ryan Hardy 03:30, 15 Apr 2005 (UTC)

It is not conventional to refer to Newtons of water, but then, one asks, why does one normally measure out peas or potatoes by the pound or kilogram, which can be considered (in violation of current standards) force? The answer is that one is measuring, or ought to be measuring mass; weight is being used as a surrogate. If a spring scale is used, one is achieving a measure that depends on the local acceleration of gravity, but if a balance is used, one measures mass. The bouyancy discussion is really almost independent of the local acceleration of gravity, unless that somehow varies grossly over the experimental region. That never holds in common experience with buoyancy, although the variations of gravity and centrifugal force do affect the geoid. When you speak of such and so many Newtons of water, you refer to a mass that depends on local gravity. It is probably better to couch everything as much as possible in terms of masses, or of densities and volumes.

Pdn 05:39, 15 Apr 2005 (UTC)

But buoyant force is a force, nonetheless, and cannot be measured in kilograms. And, since you have to use subtraction attain that measure of force, the units of measure cannot be changed during the operation(kg-kg ≠ kg∙m/s²). Algebraically, it would make sense to use the term "weight" in the context of force.

If Newtons are unsuitable, then is the kilogram-force a possible option?--Ryan Hardy 21:40, 15 Apr 2005 (UTC)

Newtons are SI units. A Kilogram a unit of mass. A Kilogram-force is a force that a body of 1 kg mass exerts under gravity and is approximately 10*1=10 newtons. But newtons are a better option as they are the Internationally accepted. Kilograms are also used to measure force assuming the gravitational force is the same everywhere om earth.--Jetru 11:59, August 23, 2005 (UTC)

Negative Buoyancy ?

Is it strictly correct to modify the word buoyancy with negative or neutral? I thought there are only two forces acting vertically on a submarine: buoyancy (upward) and gravity (downward) ? I have heard submariners speak of negative/neutral buoyancy, but I think this is not strictly scientifically correct (much the way non-professionals use the gram/kilogram as a unit of weight rather than mass). Perhaps this distinction should be made for the sake of strict accuracy?Wikkileaker (talk) 19:07, 5 December 2016 (UTC)

Best to post at the bottom of the talk page, as folks often won't notice a post inserted into the middle, and you might not get replies.

Strictly, you're right. A scuba diver is subject to the downward force of gravity and a buoyant upward force which is due to the displacement of the surrounding water. Strictly, the latter force is "buoyancy". Nevertheless, scuba divers, submariners and others tend to describe the net force (buoyancy - gravity) as "positive buoyancy" if the net force is upwards; "negative buoyancy" if the net force is downwards; and "neutral buoyancy" if the net force is zero. That convention is so widespread among those groups – and hence the sources that discuss those activities – that it would be a disservice to our readers if we were to omit those phrases. --RexxS (talk) 20:27, 5 December 2016 (UTC)

This sounds reasonable, but I was wondering if it's worth the bother to insert a sentence making the distinction clear, for sticklers such as myself?  :)Wikkileaker (talk) 21:40, 6 December 2016 (UTC)

Sure, why not? What sentence did you have in mind? --RexxS (talk) 23:32, 6 December 2016 (UTC)

Please let me get back on this...am juggling too many projects just now!Wikkileaker (talk) 20:42, 7 December 2016 (UTC)

Comment on article quality recovered from article

{{This article has numerous errors and hidden assumptions. Additionally, it is much longer than it should be for an encyclopedia article (in my opinion). It should cross-reference important related topics. Notably missing is a link to the equations of motion in a Newtonian fluid from which the hydrostatic relationship is derived with certain assumptions. Surface tension is mentioned as a missing force, but that derives from the boundary condition at a free surface of the fluid. It should probably be rewritten from scratch by an expert. I tried editing it but gave up in frustration, and I do not have time to write a new article to replace it. By the way, I have a Ph.D. in physical oceanography and have worked on ocean and atmospheric physics for more than 40 years. I came to this article with the hope that it would help me in writing a journal article to address problems in the oceanographic literature regarding air-sea buoyancy fluxes. I can see that the confusion extends well beyond oceanography.}

Comment inserted into article by RLapin at https://en.wikipedia.org/w/index.php?title=Buoyancy&type=revision&diff=781129652&oldid=778671834 and transferred here by myself. • • • Peter (Southwood) ^(talk): 08:29, 19 May 2017 (UTC)

RLapin, Your comments are now here for anyone to see and to respond as they see fit. If you are not already aware, Wikipedia is written by people who have the time and inclination but not always the specialist knowledge, so we rely on other Wikipedians to review and correct things. Pointing out problems can help, if they indicate specific problems, as you have done above in a few cases. We now wait for someone with the time and interest, and hopefully some understanding of one or more of the issues mentioned, to make improvements. • • • Peter (Southwood) ^(talk): 08:36, 19 May 2017 (UTC)

Almost any encyclopedia article will contain hidden assumptions and it is always a matter of judgement how much the target audience for the article can be assumed to know. This has long been a problem for this Wikipedia article as it used as a homework reference by high-schools pupils and apparently by PhDs writing journal articles. Since the article attempts to cater for such a wide spectrum, it is hardly surprising that it is much longer than a reader may have expected. It has actually had a sizeable section on dynamic buoyancy removed. Are you saying it should cover dynamic buoyancy, including the effects of drag and viscosity as well? Wouldn't that make it even longer? I personally don't believe the article has any errors, and until someone actually points to a specific issue, I'm inclined to take a report of "numerous errors" rather skeptically. I'm sure it should cross-reference important related topics, but without a hint as to what these "important related topics" are, it's difficult to link them. We do have an article on Newtonian fluids, but it is by no means obvious how that should be linked from this article. I'd be happy to see a proposed re-write from an expert, but – as you make clear – experts are always too busy to write general encyclopedia articles for no reward. --RexxS (talk) 09:37, 19 May 2017 (UTC)

Air-sea buoyancy flux as a subject before our "buoyancy" article would probably benefit best from readings about atmospheric fields. Related we do have Atmospheric sciences, Atmospheric chemistry and Atmospheric physics. That last would lead to Cloud physics which mentions a "buoyant convective upward motion", basicly buoyancy flux although that's only short of describing the full phenomenon of course. So do we have, Convective lift, and Atmospheric convection. There was in the past a paragraph "Buoyancy of air" in the present "Buoyancy", conceptually, not uninteresting [1]. Two main flaws in it were that water is often considered incompressible in mechanics, and following a similar pattern of paradoxes due to the versatility of language, no surface of the atmosphere, by definition, may exist. Now Atmospheric escape#Thermal escape mechanisms could give the start of inspiration for expert writing on boundary fluxes phenomenons. --Askedonty (talk) 21:24, 19 May 2017 (UTC)

Understanding through etymology

Etymology please. — Preceding unsigned comment added by 87.91.248.85 (talk) 08:39, 27 January 2019 (UTC)

Buoyancy comes from "buoyant" which comes from "buoy". The OED says: "15th cent. boye corresponds to Old French boye (Diez), boyee (Palsgrave), modern French bouée , Norman boie (Littré), Spanish boya , Portuguese boia ‘buoy’; Dutch boei , Middle Dutch boeie ‘buoy’, and ‘fetter’; the same word as Old French boie , buie , boe , bue , beue , Provençal boia , Old Spanish boya fetter, chain < Latin boia halter, fetter; applied to a buoy because of its being fettered to a spot. It is not clear whether the English was originally from Old French, or Middle Dutch." Dbfirs 22:33, 27 January 2019 (UTC)

Reverts

I've just reverted two edits by AnonMan64. The change to the lead asserted that lift on an aircraft wing was the same as buoyancy, which is untrue as lift patently depends on the forward motion of the wing and Bernoulli's principle. The second merely repeated the content of sentence following it. --RexxS (talk) 19:52, 3 July 2020 (UTC)