Talk:Relative density/Archive 1

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Archived Discussion Page for Relative density

General Discussion

there are differences between mass and weight. why the dictionary still make such confuse in its relative density page? -unsigned comment, 2004

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,

${\frac {0.292{\mbox{ lb/in}}^{3}}{0.03612149{\mbox{ lb/in}}^{3}}}=8.08$

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 :)

It that the prices of cake & bread per loaf/cake, per slice, per mass, per volume, per food energy content, per content of vitamines & minerals weighted according to recommended daily intake, per tastiness, ... ? JIMp _talk·cont 04:37, 13 June 2008 (UTC)

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

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.

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)

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)

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)

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)

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 (This cmnt Was added by User:12.226.98.83) --Bduke 07:15, 16 January 2007 (UTC)

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