Talk:Density

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Add to table: High density liquids at room temperature[edit]

Methylene Iodide is unique in that it is a dense (3.325 g·cm−3) room temperature liquid and also an organic compound. It is useful in chemistry laboratories as a methylenating agent and for rare metal / diamond testing & refining.

There is also Clerici solution (thallium formate plus thallium malonate in water). It is liquid at room temperature, with a density of 4.25 g/cm3, however this increases to 5 when warmed. It, along with methylene iodide, are useful for prospecting as they tend to cause precious metals to sink away from ore particles. With Clerici solution, the opposite occurs and diamonds float on it's surface. Another key to their usefulness in this application is that they do not form alloys or react with the items being refined, as gallium might.

Gallium's solid density is 5.91 g·cm−3 but it's melting point is just 29.76 Celsius (where it's density becomes 6.095 g·cm−3).

Various gallium alloys exist that are liquid at room temperature and below, e.g. Galinstan. Melting point, -19 Celsius. Density, 6.44 g/cm3 at STP. This has possible applications as a coolant and it, with gallium it's self, are of interest to electronics and semiconductor manufacturers.

Bromine is another example, at 3.1028 g·cm−3 and boiling at 58.8 °C.

I believe these would make interesting additions to the table as they all have useful properties based on them being dense liquids at, or near, room temperature. A check of google for 'densest liquid' quickly highlights the number of people asking the same thing; with the sole response commonly being 'mercury'. Those examples sweep a good selection of different forms (e.g. none metallic element, metal, metal alloy, organic compound, solution).

No title[edit]

"...but not the densest materials." What are the densest materials ? What is denser than osmium ? — Preceding unsigned comment added by 165.222.184.132 (talk) 12:14, 13 October 2011 (UTC)

Not sure where to ask this, so I'll just put it here. On the table for #Densities_of_various_materials, could this be cleaned up, so it can be properly sorted by density? i.e. Removing intangible things or putting them in a separate table. Such as the Sun, core of the Earth, black hole, etc.. Thanks.209.150.195.106 (talk) 22:59, 10 November 2011 (UTC)

I was thinking the same thing. Working on that now! Dudecon (talk) 23:50, 13 February 2012 (UTC)
What a terrible idea!!! You messed up the whole table. Now it's very difficult to read and compare. It's called SCIENTIFIC notation for a reason!

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Gravity is a special case of Density with two objects or more[edit]

may be, Gravity is a special case of Density the electron does not spin fast enough to merge with the nuclei of the atom, i.e. lower mass/vacuum energy momentum torque of electron to that of the nuclei of the atom, may be because of the electron's smaller mass radius in comparison to the atom's larger radius. when moving to a higher vacuum energy density (may be because larger mass of the nuclei accumulate larger vacuum energy vector near or on it's surface with it's own torque momentum with vacuum energy)near the nuclei of the atom: electron loses photon because it must spin faster (higher torque momentum of the electron's matter surface resistance vector and the vacuum energy vector which leads to a higher spin of the electron),noting: lower energy vacuum space energy with higher energy matter of the electron and/or the nuclei of the atom. density= matter/vacuum energy--99.109.130.141 (talk) 03:54, 7 October 2010 (UTC)--e:Y,?:G 03:55, 7 October 2010 (UTC) I have initiated this discussion about Density because I have not read an article (or I could not find one) where the topic is: Density of matter in vacuum or Density of matter with respect to vacuum energy, which is very important to physics.--e:Y,?:G 04:15, 7 October 2010 (UTC) —Preceding unsigned comment added by E:Y,?:G (talkcontribs) in other words, could it be that: if and where matter is inside vacuum i.e. vacuum energy and at vacuum large enough in volume, density = matter/vacuum energy is higher,denser energy medium i.e. matter/lower,lesser energy medium i.e. vacuum energy

then

the lower, lesser energy medium i.e. vacuum energy would want to "dilute" the higher, denser energy medium i.e. matter; therefore, the inward force exerted by lower, lesser energy medium i.e. vacuum energy onto the higher, denser matter.--e:Y,?:G 04:47, 7 October 2010 (UTC) —Preceding unsigned comment added by E:Y,?:G (talkcontribs)

Density of a black hole[edit]

I it may be a stupid question but isn't the density of a black hole infinite? I mean isn't that kind of how a black hole is defined, as a point in space with no extent, a specific mass and infinite density. and that is why light can't escape.

No. The "singularity" at the center of a black hole might be a point in space with no extent, but there's no way to tell, because if you're closer than a specific distance from the center, even light (or radio signals) pointed straight away from it can't get away. This distance, called the Schwarzschild_radius, defines the sphere surrounding the singularity, called the "event horizon", from within which light cannot escape.
Interestingly, all black holes rotate, and the rotation deforms the black hole's event horizon. I don't know if this alters the enclosed volume or not... a better physicist than I will have to answer that one. Dudecon (talk) 04:46, 2 August 2014 (UTC)
You can take the mass of a black hole, and divide by the volume of this sphere, to get a value with units of density. If you take a black-hole and double its mass by throwing in more matter, its radius will also double -- so interestingly, the more massive a black hole is, the less dense it is.
Example: If you took the Earth (6×1024kg) and compressed it to a "point in space with no extent", the closest you could get to that "point" and still radio out would be 9mm. That's a peanut-sized volume 3cm3 in size, for a "density" of 2×1030kg/m3.
On the other hand, the super-massive-black-hole at the center of the Milky Way Galaxy is around (9×1036kg), one and a half trillion times more massive. Its radius (13.5 million km) is larger by the same factor, for a "density" of 9×105kg/m3. That's still denser than "the core of the Sun", but way lower than an Earth-mass black hole. (User not logged in) 03:32, 8 March 2013 (PST)
....
You know, given that a black hole's density drops as its mass increases, it's incorrect and misleading that the article lists black holes as having the single, inconceivably-huge density of 2×1030kg/m3. An Earth-mass black hole is impossible primarily because there's no known force capable of compressing material to such a density. Given that they're impossible, perhaps their density doesn't belong in the article.
The least massive black holes that actually exist are several times the mass of the Sun, and this (higher) mass corresponds to a (lower) density, comparable to the density at the core of a neutron star, (1×1018kg/m3 according to this article), making that pretty much the highest density possible. From that point on, the more mass you pour into the black hole, the less dense it gets. — Preceding unsigned comment added by 76.77.184.22 (talk) 09:25, 6 April 2013 (UTC) I changed the table so now it gives densities for stellar-mass and supermassive black-holes (which exist), rather than Earth-mass black holes (which don't).
Perfect. I like the way the article deals with black holes now. Specific example masses with specific densities. Well done! Dudecon (talk) 04:46, 2 August 2014 (UTC)


If it doesn't have infinite density, then some amount of radiation can escape and then it's not a black body.Rphb (talk) 21:17, 23 June 2012 (UTC)

All that is required for a black hole is a gravitational gradient with an escape velocity which exceeds the speed of light. A body doesn't have to be anywhere near infinite density to achieve this. Singularities have never been observed, and may very well not exist. Dudecon (talk) 04:46, 2 August 2014 (UTC)

Density of nonideal solutions[edit]

Measurements of densities of solutions/mixtures can be used to determine activity coefficients. This statement has been labeled as unsourced.--193.231.20.25 (talk) 10:11, 14 January 2014 (UTC)

There is no real need to be sourced.--193.231.20.25 (talk) 13:30, 15 May 2014 (UTC)

I see no equations or qualitative relationships given (the term "activity" doesn't even appear in this article), nor is there anything in activity coefficient explaining specifically how that parameter directly mathematically affects density. DMacks (talk) 22:48, 15 May 2014 (UTC)
The activity coefficient has some formula linking excess volume and enthalpy to activity coefficient. It is known that these excess quantities are equal to the volume and enthalpy of mixing having non-zero values in non-ideal solutions where also the activity coefficient differs from unity. Of course some equations must be inserted to provide context for the statement discussed here.--188.26.22.131 (talk) 10:03, 19 May 2014 (UTC)
In this relation which express density as a function of the densities of pure components of the mixture and their volume participation in mixtures with no interaction between the components:
\rho = \sum_i  \rho_i \frac{V_i}{V}.\,
necessary substitutions could be made.--188.26.22.131 (talk) 10:15, 19 May 2014 (UTC)
like V= \sum_i V_i + \sum_i V_i^{E}--193.231.20.25 (talk) 11:26, 20 May 2014 (UTC)

What is the relationship between Denstiy and Scratch resistance?[edit]

What is the relationship between Denstiy and Scratch resistance? — Preceding unsigned comment added by 193.194.132.70 (talk) 12:04, 1 August 2014 (UTC)

Scratch resistance has more to do with hardness and elasticity than with density. There is probably some correlation between low density and low hardness, but high density is no guarantee of hardness or scratch resistance. For instance, Gold is very dense, but scratches easily because it is soft and inelastic. Tungsten Carbide is dense, but also very hard and is highly resistant to scratching. Rubber is not hard, but very elastic, and because nearly all of the deformation is non-permanent, it is hard to scratch. Dudecon (talk) 04:31, 2 August 2014 (UTC)

Semi-protected edit request on 4 January 2015[edit]

Correct the units in the table "Densities of various materials covering a range of values". It is support g/cm^3, not kg/m^3. Maxralf (talk) 16:59, 4 January 2015 (UTC)

X mark.svg Not done as the existing units are correct - e.g. water weighs 1,000kg (1 Tonne) per cubic metre, it does not weigh 1,000g (1 kg) per CC. - Arjayay (talk) 17:19, 4 January 2015 (UTC)

Edit Request: "Common Units" Should Show Actual Density Terms[edit]

The subsection for U.S. Customary Units under the Common Units heading makes conflicting statements. It includes both lb/ft^3 and slugs/ft^3 as possible density units. This is physically incorrect, as noted in another section, as lb/ft^3 is a term for unit weight. Slugs/ft^3 is the only correct term in the set.

If the common usage of lb/ft^3 in place of density is to be noted, that should be NOTED in the units section so that a person does not conclude that weight/volume is the proper way to calculate density, as we know that mass/volume is the definition of density.

Please make this edit. Thank you. — Preceding unsigned comment added by 129.252.33.12 (talk) 21:42, 25 January 2015 (UTC)

The mass versus weight confusion is common for the unit of "pound". Our Pound (mass) article seems pretty explicit that "lb" is a standard unit of mass (correlates with kilogram), whereas the Pound (force) defines based on it (the force of the mass at earth's gravity); the force sense is not the fundamental unit. Note that the first time the term is used as a US unit, it's called (and linked) explicitly as "Avoirdupois pound", which is by definition specifically the mass-unit not the force-unit. DMacks (talk) 04:06, 26 January 2015 (UTC)

Semi-protected edit request on 10 February 2015[edit]

The table of approximate material densities needs to be corrected. The density units in the header are in kg/m^3 so that air is shown correctly at 1.2kg/m^3. What is then incorrect is to show water as 1kg/m^3 and I suspect a lot more of the solid materials in the table also need to be increased by 1000. These figures have probably been taken from another table with units of g/cm^3. For instance Gold is shown as 7.? whereas I'd expect a cubic metre of gold to be many tonnes - probably 7000 kg or so and water, not 1.0 but 1000 as it shows in an earlier table. 86.190.18.53 (talk) 17:58, 10 February 2015 (UTC)

X mark.svg Not done I cannot see a "Table of approximate material densities" but assuming you mean the "Various materials" table, Water does not say 1kg/m³, it says 1,000kg/m³ that is a comma not a stop. As for the Gold figure, I can only see 19,320 not 7.? - Arjayay (talk) 18:14, 10 February 2015 (UTC)

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