Talk:Relative density

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Contents 1 Early talk that was placed above previous headers 2 Fahrenheit 3 this page had been vandalised 4 Cleanup 5 User comment in article 6 Removed... 7 Someone needs to sanity-check the figures in the article 8 Major copy edit proposed 9 Biogas 10 Kidneys 11 sink'n' float 12 Move? 13 Inconsistent article 14 Water density 15 Overhaul of the page

[edit] Early talk that was placed above previous headers

there are differences between mass and weight. why the dictionary still make such confuse in its relative density page?

I don't see where this article confuses mass with weight. What portion of the text are you referring to? --Diberri | Talk 18:28, Aug 6, 2004 (UTC)

Yes, it does confuse the two. One need only search the page for the words "weight" and "mass" to see it.

Not only that, the method for measuring it at the end is incorrect. Subtracting the two measurements does not give the weight of the displaced water. It gives the weight of the dry sample. However if it is intended that inserting the sample will cause overflow of some water (not clear from the description) it gives the sample dry weight minus that volume of water.

This page needs some help.(by User:148.63.121.89)

Remember, be bold in editing articles. If you can improve this or any article... just do it. No need to discuss the page's problems here first. If you make changes and others disagree, we'll discuss it here. ike9898 22:20, Mar 25, 2005 (UTC)

Lots of pages can use some help. But if you want to claim confusion, you need to specify it.

One of the biggest problems with the whole concept involved in this article is that using "specific gravity" or "relative density" is a stupid idea in the first place. Just talk about density, and use units of density. That's not so damn hard to do, is it? Are you really so lazy that you can't be bothered to use the units? Usint the units sure avoids a whole lot of confusion about what the temperature is of the water to which it is being compared, and whether or not that is the same temperature at which the other quantity's "specific gravity" is being measured.

Like Ike9898 says, if you think it needs fixing, jump in and fix it. That's the easiest way to do it. But in any case, it might help to keep in mind a couple of other things:

1. The word "weight" is an ambiguous word, one with several different meanings. It's best to avoid it in a technical context.
2. If you are dividing out ratios, it doesn't make one bit of difference whether you are comparing the mass of the object being measured to the mass of the displaced water, or if you are comparing the force which that object exerts due to gravity at the location at which it is being measured, and the force due to gravity of the water it displaces, which had been in the very same location and was affected by the very same gravitational field. The ratio is exacty the same, either way.

With that last part, especially, in mind, please be specific about how it is going to make any difference whatsoever, if you want to claim any "confusion" on anybody's part.

Gene Nygaard 22:52, 25 Mar 2005 (UTC)

this DOES NOT ANSWER MY QUESTION??//////// WHY RELATIVE DENSITY HAS NO UNITS [unsigned by User:209.94.195.209 14:27 UTC 9 November 2005]

Please sign your posts by using four tildes ~~~~ even if you are not a logged-in user.

It doesn't have units because it is "relative" to the density of something else. For example, suppose you have a piece of iron with a density of 0.292 lb/in³, and you compare it to the density of water at 32 °F, which is 0.03612149 lb/in³. When you divide them out,

As you can see, the units will cancel out. That's why there are no units. You will also get the very same number without units if you give both densities in units of Mg/m³, for example. Gene Nygaard 15:07, 9 November 2005 (UTC)

That's correct reasoning but requires (some) knowledge of algebra. The non-mathematical and just as valid reason is that the relative density is density of something relative to something else. The relative price of cake to bread is 5. Not 5 dollars, not 5 pennies, not 5 dinari, just 5. It's 5 times the price, whatever the unit. And the relative density of aluminium to water is 2.7 - no matter what units you use. Paul Beardsell 04:21, 18 November 2006 (UTC)

Sir, I dispute your assertion that cake is five times more expensive than bread. You have provided no evidence to support this claim, and I find it misleading and inacurrate.

(teehee, just kidding :)

[edit] Fahrenheit

Why on earth does this include Fahrenheit, surely only celsius or Kelvin should be used? Owwmykneecap 00:28, 12 June 2006 (UTC)

it is really confusing.. who discovered it :I do not know and you can not find it on the internet

[edit] this page had been vandalised

see message <dia6f25ijgq5ovhff0hv0fbu5prk89v4m4@4ax.com> in newsgroup alt.punk I thought I'd revert it, but then changed my mind. This whole article doesn't make any sense anyway, and the vandalised table wouldn't belong in it even if it did.

[edit] Cleanup

I've added a cleanup sticker - because too many editors are signing their contributions and the article as a whole is becoming disjoint. It needs:

1. Signatures in this discussion page - not the main article
2. Clean-up of the current version
3. Any future comments on the article to be discussed here - and not in the article itself.
4. The consensus of any discussion to be applied to the main article.

Thanks Ian Cairns 23:09, 17 October 2006 (UTC)

[edit] User comment in article

The following user comment was removed from the article:

"EDIT: Comparison to water would give 0.001227 and is not appropriate. Specific gravity of biogas should be related to density of air at standard conditions (approximately 1.29 kg/m³ at 0 degrees Celsius and pressure of 1 atmosphere absolute). Hence for Biogas with density quoted above specific gravity would be 0.95. Specific gravity of gases is also sometime defined as ratio of molecular weight of gas to molecular weight of air.[A.F.Gawin]10:50, 16 October 2006 (UTC)87.101.240.7"

Khatru2 05:30, 20 October 2006 (UTC)

[edit] Removed...

This Table of temp vs density presented here is not accurate maximum density of water occurs at 4C (3.98C to be accurate) and is 1000kg/m3. the density then decreases with temperature to about 997.07 kg/m3 at 25C. Actually reference a CRC Handbook at a university or book store. Ice at 0C is 999.87 kg/m3.

I removed this since it doesn't fit with the rest of the article. Comments? --M1ss1ontomars2k4 ^{(T | C | @)} 06:33, 31 October 2006 (UTC)

[edit] Someone needs to sanity-check the figures in the article

I just noticed this in a google search for how to vandalize wikipedia:

http://www.gatago.com/alt/punk/27435323.html

Note the diff at the bottom of that page. -- Jim Douglas ^(talk) _(contribs) 20:45, 8 November 2006 (UTC)

That diff is back in August and was on the table of calculated values from a formula in the CRC Handbook. These were replaced more recently by experimental values so I think the vandalism has been reversed. However I do not have the book the values came from. Can someone check it? --Bduke 22:45, 9 November 2006 (UTC)

[edit] Major copy edit proposed

The problem with this article is that it goes in depth into related issues and this is not required. The density of water is not an issue to be discussed in any detail here. I am proposing a major re-write which will say everything there is to be said about relative density directly, with links to air and water and density and other articles too. Therefore, the article will be MUCH SHORTER. Paul Beardsell 04:15, 18 November 2006 (UTC)

I agree with many of your points. However, I think the article should be re-named "Specific gravity" and re-written. The vast majority of readers having any knowledge whatsoever of chemistry, engineering or physics are much, much more familiar with the term "specific gravity" ... so why get involved in arcane terminology like "relative density" ... and why introduce those who have no knowledge of chemistry, engineering or physics to an arcane term that is not commonly used? - mbeychok 06:12, 18 January 2007 (UTC)

[edit] Biogas

The information about 'Biogas' was neither relevant nor correct. While it is important to discuss the specific gravity of water (as it's 1000 kg/m^3/1 g/cm^3 approximate value makes it a useful substance for comparison in calculations and for demostration of the basic concepts of specific gravity), no more information is needed about methane than its density (found more reliably under methane, and as 'Biogas' is a general term for a varying mixture of hydrocarbons, i have decided to delete all that shizzle nizzle.

Love, Tim (Above moved from top. Was added by User:12.226.98.83) --Bduke 07:15, 16 January 2007 (UTC)

[edit] Kidneys

I suggest that the material relating to the kidney be moved to Kidney or to Kidney function or, if we must, to Specific gravity (kidney). The kidney is a machine (a living machine, an organ) and an important one but there are numerous machines (and organs) for which the specific gravity of a solution or suchlike is important. This article should say what RD / SG is and describe that BUT discussion of machine / organ function and medical treatment details / engineering maintenance instructions should be moved to the page about the organ / machine. Material should not be duplicated at WP - it should be linked to. Move imminent. What say you? Paul Beardsell 23:33, 19 January 2007 (UTC)

Move to a subsection of Kidney function. This is so random an inclusion in this article it is laughable! SauliH 00:00, 20 January 2007 (UTC)

I've cut the material. I'll put it here in case anyone wants to rescue it for inclusion in a more appropriate article. Paul Beardsell 21:22, 22 January 2007 (UTC)

Actually, in the clinic, when we say "specific gravity", we are referring to specific gravity as it relates to kidney function and not "specific gravity" in a general sense. So, it's really not all that surprising (or laughable for that matter) that an editor included the renal discussion in this article, as anyone with a medical background will likely arrive at this article when searching for information on urinary specific gravity. Given that, I'd suggest moving the text in question to Specific gravity (kidney) and highly suggest linking to it from this article or from a disambiguation page. The article on Kidney function covers general issues of kidney physiology and would not be appropriate for a clinical concept like specific gravity. Jay†Litman 17:48, 1 February 2007 (UTC)

I went ahead and moved the text to Specific gravity (kidney). There are also several articles on WP that link readers to specific gravity for further information on urinary specific gravity. I'll try to fix as many as I can. Jay†Litman 14:55, 2 February 2007 (UTC)

[edit] sink'n' float

relative densities are not about liquids (only). I will be removing the para that goes on about sinking and floating "in the reference [substance]" as if the reference could only be a liquid, as if the other substance is not itself another liquid, as if the the other substance would not dissolve! Too clever. Paul Beardsell 07:08, 29 January 2007 (UTC)

Actually, the concept of "sinking and floating" also applies to the relative density of gases, as gases with a realtive density greater than 1.0 will "sink" below the reference gas. For example, if you have a mixture of nitrogen and carbon dioxide at room temperature, the carbon dioxide will "sink" to the bottom of the mixture. I'm not sure that removing the section will necessarily help, but I would suggest substituing the word "float" with "rise." I think "float" is little less descriptive, and possibly misleading for some people. Jay†Litman 15:09, 2 February 2007 (UTC)

You miss the point. Relative density is not only to do with fluids (which, by the way, includes both gases and liquids) but also with solids. Paul Beardsell 21:36, 2 February 2007 (UTC)

You're right. I don't see your point. I'm well aware that relative density applies to more phases than just liquid, as should be evident from my response above, but I still don't see why the paragraph on "sinking and floating in a reference substance" should be removed. I would rather see it revised. Perhaps an extra sentance or two expanding on relative density as it relates to different phases. Jay†Litman 22:33, 2 February 2007 (UTC)

Sinking and floating depends upon gravity as well as relative density. In space relative density survives but there is no buoyancy. What you want to write about is well covered at the buoyancy article. That's the place for it. Paul Beardsell 05:41, 8 February 2007 (UTC)

Also: Light salt "sinks" past heavy stones. This sinking and floating is a nonsense and should not be here. Paul Beardsell 05:42, 8 February 2007 (UTC)

Leave as is. It demonstrates a simple concept that most readers will be familiar with; but yes, you need gravity for it to be true, but I really don't think anyone will care since this concept really only is used on Earth. The same "float" "sink" concept applies for solids ... how do you think Plate tectonics works? The term "float" is not a toy concept term ... continents (or crust) really do float on asthenosphere, and none of these solids! +mwtoews 09:36, 8 February 2007 (UTC)

No. I'm removing. It's buoyancy. Paul Beardsell 10:25, 8 February 2007 (UTC)

You really didn't explain why you don't like it, and I'll argue that your "improvement" is in the wrong direction, as there was nothing inaccurate about "sink" and "float" (where there is gravity), and most readers can understand that concept better. Certainly yes, buoyancy is the force coupled with gravity that allows things to actually float, but now you've lost John Q Public as he is trying to figure out his alcohol content in his home-brew! Your initial argument about liquids is stale in this discussion since clearly the "float"/"sink" concept works for solids and fluids; so please elaborate why you made this change. +mwtoews 17:48, 8 February 2007 (UTC)

I did explain why, and well enough. But that is not to say that more explanation is not possible. I note however that you do not address arguments I have already made above. But here goes: (i) What is happening, by bringing in "sink and float" here, is conflation of two separate albeit related concepts as if they were equivalent. This, it goes without saying, is bad. (ii) This is happening in the introductory paras of the article - the last place for it! (iii) Sink and float does NOT work well for solids, see salt'n'rock arg above for just one example. (iv) Sink'n'float requires gravitation (or other acceleration) but this is not mentioned in this article. (v) What is being described is buoyancy but this is not referenced. (vi) The home brew will dissolve in the reference substance and never float nor sink. I could go on and on. If you want to mention sink and float then please do so, later in the article, not in the intro, and clearly referening buoyancy. Thanks. Paul Beardsell 20:43, 8 February 2007 (UTC)

OK, thanks for specifying your exact reasons. I agree that it is a separate/related concept, so should not appear in the intro para, and we'll leave your edits as is. I may add it later (time-wise and article-wise), as an example behaviour, and spell out the conditions in which the related concept holds true. The only reason why I consider this detail important is in the interpretation of the numeric value of relative density, for d < 1, d > 1 and d = 1. (In general, this article needs a bit of work.) Also, in the home brew example above, I was referring to one of these; dissolving does not apply here—its just a relative measure of sinking-ness or floating-ness to determine alcohol content. +mwtoews 21:12, 8 February 2007 (UTC)

Yes, this article needs work. I certainly was not advocating the return to some previous version. As happens so often at WP this article is improved by to and fro argumentdiscussion that happens on the talk pages. Paul Beardsell 03:24, 9 February 2007 (UTC)

[edit] Move?

I think this page ought to be moved to Specific Gravity. The term relative density has meanings other than Specific Gravity - i.e. the denominator is not always the density of water. SG, however, is always relative to water. Toiyabe 19:07, 13 March 2006 (UTC)

I agree wholeheartedly. The vast majority of readers having any knowledge whatsoever of chemistry, engineering or physics are much, much more familiar with the term "specific gravity" ... so why get involved in arcane terminology like "relative density" ... and why introduce those who have no knowledge of chemistry, engineering or physics to an arcane term that is not commonly used? - mbeychok 06:07, 18 January 2007 (UTC)

Coming from a gemology perspective, I would much prefer readers linking from gemology articles land on an article about SG not 'relative density'. SG is an article very much in need of writing, as it is used in various fields of study - relative density doesn't cut it. Can someone who knows the subject area take care of this please? SauliH 07:58, 19 January 2007 (UTC)

I've written a short description of SG. SG is specific in that it intrinsically refers to the standard substance as water. To speak of just relative density, leaves the question of which standard substance used unanswered. The article on Relative density also seems to cover topics which to me seem better explained and covered elsewhere. Pae_nor Oslo, Norway, 18:48, 14 February 2007

The content from specific gravity has been merged into this article, and some distinctions have been made to try and point out the subtle differences between the terms. That is that SG has a reference density as water, while relative density is more general. Please feel free to expand on this. +mwtoews 20:59, 14 February 2007 (UTC)

[edit] Inconsistent article

This article is in need of some cleanup. The article is inconsistent, inaccurate and somewhat verbose. E.g it states that relative density is both similar and the same as Specific gravity. Also, it is inaccurate to state that "quantify the buoyancy between two materials": Bouyancy is, simply stated, an upward force as experienced by an object wholy or partly immersed in a surrounding fluid (gas or liquid), i.e substances incapable of sustaining shear forces. Calculation of SG can be done irrespective of units used, as long as the units used are consistent, i.e. don't divide slugs/ft3 with kg/m3... When it comes to Specific gravity (SG) i still feel that the article I wrote is more accurate w.r.t SG and should not be redirected. Pae_nor 09:52, 15 February 2007 (UTC)

Yes, I'll agree that the article needs a good revision, and some of the content is questionable and needs references. However, splitting this article into Relative density and Specific gravity articles is not desirable, as these are very similar, as the only difference that I am aware of is:

Am I missing something? (Also, I'm unsure of what a more proper notation for relative density should be ... ideas?) +mwtoews 18:05, 15 February 2007 (UTC)

[edit] Water density

since density of water is (approximately) - I am no physics expert but I had been taught that the metric system was designed around the physical characteristics of wtaer - meaning the density of water would be precisely as stated and not approximate. Am I wrong? SauliH 18:29, 27 February 2007 (UTC)

The metric system was only sort-of based on 1kg=1L of water, and for many calculations, this assumption works just fine. However, as it turns out the density of water is not constant, as it is temperature dependent (everything is—not just water). That's why lakes stratify in the winter (4°C at the bottom, since it is densest). The metric system is now based on the wavelength by an atom of cesium-133 and the such.+mwtoews 01:23, 28 February 2007 (UTC)

Ok. You learn something ne... Cheers!SauliH 01:49, 28 February 2007 (UTC)

[edit] Overhaul of the page

I did a recent semi-overhaul of the page. But I'm not an expert, I'm just an engineering college graduate who got A's in his physics classes and math classes. I know the power of using natural units and I appreciate using unitless dimensions. Hence the large section for the unitless properties of RD. Also, my physics proff. wanted us to demonstrate the hydrometer problem shown. I figured it was important enough to be encyclopedic. I've got a second proof, showing that a hyperbolic cross sectional area would create a linear relationship between displacement and change in RD, but decided it was not encyclopedic enough to warrant placing it on here. Since it required the use of calculus, I doubt most readers would understand it as well. (Also, I'm not quite an expert, as I've said before.)

If anyone has grammar issues, spelling issues, etc... change up the page. I'm not a grammar expert, and I don't know how to program this math code for beans. If anyone thinks the math isn't important enough to warrant placing here, let me know and I'll just put it on my talk page. I don't have any source for the proof I listed concerning the hydrometers, but I did cite other wiki pages which had sources and used basic algebra for my proof. Let me know if you think this info is usefull or not. --Markozeta 01:35, 13 March 2007 (UTC)