density
American Heritage Dictionary:
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den·si·ty
(dĕn'sĭ-tē) 
n., pl., -ties.
n., pl., -ties.
- The quality or condition of being dense.
- The quantity of something per unit measure, especially per unit length, area, or volume.
- The mass per unit volume of a substance under specified conditions of pressure and temperature.
- Computer Science. The number of units of useful information contained within a linear dimension.
- The number of individuals, such as inhabitants or housing units, per unit of area.
- The degree of optical opacity of a medium or material, as of a photographic negative.
- Thickness of consistency; impenetrability.
- Complexity of structure or content.
- Stupidity; dullness.
Wiley Book of Astronomy:
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density
The ratio between the mass of an object and its volume. In the metric system, density is measured in grams per cubic centimeter (or kilograms per liter).
Densities of Familiar Substances and Objects
| Object/Substance | Density (g/cm3) |
| water | 1.0 |
| iron | 7.89 |
| Sun | 1.41 |
| white dwarf | 2 × 106 |
| neutron star | 7 × 1014 |
| Venus | 5.2 |
| Earth | 5.52 |
| Mars | 3.94 |
| Jupiter | 1.31 |
| Saturn | 0.69 |
| Uranus | 1.29 |
| Neptune | 1.64 |
| Pluto | 2.03 |
Britannica Concise Encyclopedia:
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density
Mass of a unit volume of a material substance. It is calculated by dividing an object's mass by its volume. In the International System of Units, and depending on the units of measurement used, density can be expressed in grams per cubic centimetre (g/cm3) or kilograms per cubic metre (kg/m3). The expression particle density refers to the number of particles per unit volume, not to the density of a single particle. specific gravity.
For more information on density, visit Britannica.com.
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The mass per unit volume of a material. The term is applicable to mixtures and pure substances and to matter in the solid, liquid, gaseous, or plasma state. Density of all matter depends on temperature; the density of a mixture may depend on its composition, and the density of a gas on its pressure. Common units of density are grams per cubic centimeter, and slugs or pounds per cubic foot. The specific gravity of a material is defined as the ratio of its density to the density of some standard material, such as water at a specified temperature, for example, 60°F (15.6°C), or, for gases the basis may be air at standard temperature and pressure. Another related concept is weight density, which is defined as the weight of a unit volume of the material. See also Density measurement; Weight.
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The amount of some quantity per unit volume, notably of mass per unit volume, termed distinctively mass density but more properly volumic mass. Used similarly for amount of substance per unit volume (see amagat unit) and for electromagnetic quantities (see SI unit for examples). Used also per unit area in the form ‘surface density’, e.g. C·m-2 for surface density of charge.
Barron's Marketing Dictionary:
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density
In general: term used as a measure of population in proportion to a geographic area.
Direct marketing: measure of the proportion of customers or prospective customers in a geographic area compared to the total population of the area.
Photography: measure of the relative blackening of photographic images, which consist of silver particles spread in varying densities onto a surface. The particles create images of light, dark, and shadow. See also densitometer.
Barron's Business Dictionary:
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density
Real estate: intensity of land use. For example, if a 10-acre subdivision contains 30 single-family houses, the housing density is 3 dwelling units per acre. If the population density is 4 people per house, the population density per acre is 12.
| Denomination, Demutualization, Demurrer | |
| Density Zoning, Dentaland Vision Insurance, Department |
Barron's Real Estate Dictionary:
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density
The intensity of a land use.
See also land use intensity.
Example: A 10-acre subdivision contains 30 single-family houses.
The density is 3 dwelling units per acre. A portion of land with minimal use of its own can often be included to meet density requirements.
A 100-acre tract is limited to a density of 4 units per acre. Zoning will allow a total of 400 units, despite the fact that 20 acres of the land is a floodplain , and no improvements are allowed on that portion. The 20
acres of floodplain land can be used to meet the density requirements so that 400 units can be built on the remaining 80 acres.
See also land use intensity.
Example: A 10-acre subdivision contains 30 single-family houses.
The density is 3 dwelling units per acre. A portion of land with minimal use of its own can often be included to meet density requirements.
A 100-acre tract is limited to a density of 4 units per acre. Zoning will allow a total of 400 units, despite the fact that 20 acres of the land is a floodplain , and no improvements are allowed on that portion. The 20
acres of floodplain land can be used to meet the density requirements so that 400 units can be built on the remaining 80 acres.
| Demolition, Demography | |
| Density Zoning, Depletion |
Roget's Thesaurus:
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density
noun
- The quality, condition, or degree of being thick: compactness, solidity, thickness. See thick/thin.
Antonyms by Answers.com:
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density
n
Definition: bulk, mass
Antonyms: openness, sparseness, sparsity, thinness
The degree of aggregation; the quantity of any entity distributed over an area per unit of areal measure, e.g., persons per acre, families per acre, or dwelling units per square mile.
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The mass per unit volume of an object; density = mass/volume. A common unit of density is the kilogram per cubic metre.
Columbia Encyclopedia:
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density
density, ratio of the mass of a substance to its volume, expressed, for example, in units of grams per cubic centimeter or pounds per cubic foot. The density of a pure substance varies little from sample to sample and is often considered a characteristic property of the substance. Most substances undergo expansion when heated and therefore have lower densities at higher temperatures. Many substances, especially gases, can be compressed into a smaller volume by increasing the pressure acting on them. For these reasons, the temperature and pressure at which the density of a substance is measured are usually specified. The density of a gas is often converted mathematically to what it would be at a standard temperature and pressure (see STP). Water is unusual in that it expands, and thus decreases in density, as it is cooled below 3.98°C (its temperature of maximum density). Density often is taken as an indication of how "heavy" a substance is. Iron is denser than cork, since a given volume of iron is more massive (and weighs more) than the same volume of cork. It is often said that iron is "heavier" than cork, although a large volume of cork obviously can be more massive and thus be heavier (i.e., weigh more) than a small volume of iron. See specific gravity.
Cosmic Lexicon:
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Density
Mass per unit volume; a measure of how much material is in a given space.
Woodbook Wood Glossary:
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Density
Weight per unit volume. Density of wood is influenced by rate of growth, percentage of late wood and in individual pieces, the proportion of the heartwood.
Word Tutor:
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density
IN BRIEF: Closeness or thickness.
The density of the insulation seemed meager because they were always cold.
LearnThatWord.com is a free vocabulary and spelling program where you only pay for results!
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The relative heaviness of objects, measured in units of mass or weight per units of volume. (See specific gravity.)
Wiley Dictionary of Flavors:
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Density
The measure of the mass per volume of an item. The bulk density describes the density of a powder. The gravity represents the density of a liquid. Specific gravity is the gravity of a liquid divided by the density of water at a given temperature. See Bulk Density, Specific Gravity.
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- a or mass density symbol: ρ; the mass of a substance per unit volume. b or linear density symbol: ρl; the mass of a substance per unit length. c or surface density symbol: ρA or ρS; the mass of a substance per unit area. Compare relative density.
- the distribution of a scalar physical quantity per unit area of space (e.g. radiant energy density) or per unit volume (e.g. charge density).
- the distribution of a vector physical quantity per unit area of space (e.g. electric current density, magnetic flux density).
- optical density. see absorbance.
| densitometer, densimeter, denitrifying bacteria | |
| density functional theory, density-marker bead, dentate |
Saunders Veterinary Dictionary:
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density
1. the ratio of the mass of a substance to its volume.
2. the quality of being compact.
3. the quantity of matter in a given space.
4. the quantity of electricity in a given area, volume or time.
5. the degree of film blackening in an area of a photograph or radiograph.
- population d. — number of animals per unit of area; important in relation to the rate of spread of disease.
- d. sampling — see sampling.
Mosby's Dental Dictionary:
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density
n
The concentration of matter, measured by mass per unit volume.
Random House Word Menu:
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categories related to 'density'
- Principles of Mechanics, Waves, and Measurement - density: mass per unit of volume; distribution per unit of space
- Physical Properties and Changes - density: mass per unit of volume
Wikipedia on Answers.com:
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Density
This article is about mass density. For other uses, see Density (disambiguation).
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho). In some cases (for instance, in the United States oil and gas industry), density is also defined as its weight per unit volume;[1] although, this quantity is more properly called specific weight. Different materials usually have different densities, so density is an important concept regarding buoyancy, purity and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but not the densest materials.[which?]
Less dense fluids float on more dense fluids if they do not mix. This concept can be extended, with some care, to less dense solids floating on more dense fluids. If the average density (including any air below the waterline) of an object is less than water (1,000 kg/m3) it will float in water and if it is more than water's it will sink in water.
In some cases density is expressed as the dimensionless quantities specific gravity (SG) or relative density (RD), in which case it is expressed in multiples of the density of some other standard material, usually water or air/gas. (For example, a specific gravity less than one means that the substance floats in water.)
The mass density of a material varies with temperature and pressure. (The variance is typically small for solids and liquids and much greater for gasses.) Increasing the pressure on an object decreases the volume of the object and therefore increase its density. Increasing the temperature of a substance (with some exceptions) decreases its density by increasing the volume of that substance. In most materials, heating the bottom of a fluid results in convection of the heat from bottom to top of the fluid due to the decrease of the density of the heated fluid. This causes it to rise relative to more dense unheated material.
The reciprocal of the density of a substance is called its specific volume, a representation commonly used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass.
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Contents
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History
In a well-known but probably apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.[2] Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass; but the king did not approve of this. Baffled, Archimedes took a relaxing immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leaped from his bath and went running naked through the streets shouting, "Eureka! Eureka!" (Εύρηκα! Greek "I found it"). As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment.
The story first appeared in written form in Vitruvius' books of architecture, two centuries after it supposedly took place.[3] Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time.[4][5]
Mathematically, density is defined as mass divided by volume:
where ρ is the density, m is the mass, and V is the volume. From this equation, mass density must have units of a unit of mass per unit of volume. As there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre (kg/m3) and the cgs unit of gram per cubic centimetre (g/cm3) are probably the most common used units for density. (The cubic centimeter can be alternately called a millilitre or a cc.) 1,000 kg/m3 equals one g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical and US customary units may be used. See below for a list of some of the most common units of density. Further, density may be expressed in terms of weight density (the weight of the material per unit volume) or as a ratio of the density with the density of a common material such as air or water.
Measurement of density
The density at any point of a homogeneous object equals its total mass divided by its total volume. The mass is normally measured with an appropriate scale or balance; the volume may be measured directly (from the geometry of the object) or by the displacement of a fluid. For determining the density of a liquid or a gas, a hydrometer or dasymeter may be used, respectively. Similarly, hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object.
If the body is not homogeneous, then the density is a function of the position. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ(r) = dm/dV, where dV is an elementary volume at position r. The mass of the body then can be expressed as
The density of granular material can be ambiguous, depending on exactly how its volume is defined, and this may cause confusion in measurement. A common example is sand: if it is gently poured into a container, the density will be low; if the same sand is then compacted, it will occupy less volume and consequently exhibit a greater density. This is because sand, like all powders and granular solids, contains a lot of air space in between individual grains. The density of the material including the air spaces is the bulk density, which differs significantly from the density of an individual grain of sand with no air included.
Changes of density
Main articles: Compressibility and Thermal expansivity
In general, density can be changed by changing either the pressure or the temperature. Increasing the pressure always increases the density of a material. Increasing the temperature generally decreases the density, but there are notable exceptions to this generalization. For example, the density of water increases between its melting point at 0 °C and 4 °C; similar behavior is observed in silicon at low temperatures.
The effect of pressure and temperature on the densities of liquids and solids is small. The compressibility for a typical liquid or solid is 10−6 bar−1 (1 bar = 0.1 MPa) and a typical thermal expansivity is 10−5 K−1. This roughly translates into needing around ten thousand times atmospheric pressure to reduce the volume of a substance by one percent. (Although the pressures needed may be around a thousand times smaller for sandy soil and some clays.) A one percent expansion of volume typically requires a temperature increase on the order of thousands of degrees Celsius.
In contrast, the density of gases is strongly affected by pressure. The density of an ideal gas is
where M is the molar mass, P is the pressure, R is the universal gas constant, and T is the absolute temperature. This means that the density of an ideal gas can be doubled by doubling the pressure, or by halving the absolute temperature.
Density of water (at 1 atm)
See also: Water density
| Temp (°C) | Density (kg/m3) |
|---|---|
| 100 | 958.4 |
| 80 | 971.8 |
| 60 | 983.2 |
| 40 | 992.2 |
| 30 | 995.6502 |
| 25 | 997.0479 |
| 22 | 997.7735 |
| 20 | 998.2071 |
| 15 | 999.1026 |
| 10 | 999.7026 |
| 4 | 999.9720 |
| 0 | 999.8395 |
| −10 | 998.117 |
| −20 | 993.547 |
| −30 | 983.854 |
| The values below 0 °C refer to supercooled water. | |
Density of air (at 1 atm)
Main article: Density of air
| T (°C) | ρ (kg/m3) |
|---|---|
| −25 | 1.423 |
| −20 | 1.395 |
| −15 | 1.368 |
| −10 | 1.342 |
| −5 | 1.316 |
| 0 | 1.293 |
| 5 | 1.269 |
| 10 | 1.247 |
| 15 | 1.225 |
| 20 | 1.204 |
| 25 | 1.184 |
| 30 | 1.164 |
| 35 | 1.146 |
Density of solutions
The density of a solution is the sum of mass (massic) concentrations of the components of that solution.
Mass (massic) concentration of a given component ρi in a solution can be called partial density of that component.
Expressed as a function of the densities of pure components of the mixture and their volume participation, it reads:
Densities of various materials
Further information: Orders of magnitude (density)
| Material | ρ (kg/m3) | Notes |
|---|---|---|
| Interstellar medium | 10−20 | Assuming 90% H, 10% He; variable T |
| Earth's atmosphere | 1.2 | At sea level |
| Aerogel | 1.5 | Lowest achieved densities |
| Styrofoam | 75 | Approx.[6] |
| liquid hydrogen | 70 | |
| Cork | 240 | Approx.[6] |
| Lithium | 535 | At STP |
| Potassium | 860 | At STP[7] |
| Sodium | 970 | At STP |
| Ice | 916.7 | |
| Water (fresh) | 1,000 | At STP |
| Water (salt) | 1,030 | |
| Plastics | 1,175 | Approx.; for polypropylene and PETE/PVC |
| Magnesium | 1,740 | At STP |
| Beryllium | 1,850 | At STP |
| Glycerol | 1,261 | [8] |
| Silicon | 2,330 | At STP |
| Aluminium | 2,700 | At STP |
| Diamond | 3,500 | At STP |
| Titanium | 4,540 | At STP |
| Selenium | 4,800 | At STP |
| The Earth | 5,515.3 | Mean density |
| Vanadium | 6,100 | At STP |
| Antimony | 6,690 | At STP |
| Zinc | 7,000 | At STP |
| Chromium | 7,200 | At STP |
| Manganese | 7,325 | Approx.; at STP |
| Tin | 7,310 | At STP |
| Iron | 7,870 | At STP |
| Niobium | 8,570 | At STP |
| Cadmium | 8,650 | At STP |
| Cobalt | 8,900 | At STP |
| Nickel | 8,900 | At STP |
| Copper | 8,940 | At STP |
| Bismuth | 9,750 | At STP |
| Molybdenum | 10,220 | At STP |
| Silver | 10,500 | At STP |
| Lead | 11,340 | At STP |
| Thorium | 11,700 | At STP |
| Rhodium | 12,410 | At STP |
| The Inner Core of the Earth | 13,000 | Approx.; as listed in Earth |
| Mercury | 13,546 | At STP |
| Tantalum | 16,600 | At STP |
| Uranium | 18,800 | At STP |
| Tungsten | 19,300 | At STP |
| Gold | 19,320 | At STP |
| Plutonium | 19,840 | At STP |
| Platinum | 21,450 | At STP |
| Iridium | 22,420 | At STP |
| Osmium | 22,570 | At STP |
| The core of the Sun | 15,0000 | Approx. |
| White dwarf star | 108 | Approx.[9] |
| Neutron star | 1017 | |
| Atomic nuclei | 2.3×1017 | Does not depend strongly on size of nucleus[10] |
| Black hole | 4×1017 | Mean density inside the Schwarzschild radius of an Earth-mass black hole (theoretical) |
Other common units
The SI unit for density is:
- kilograms per cubic metre (kg/m3)
Litres and metric tons are not part of the SI, but are acceptable for use with it, leading to the following units:
- kilograms per litre (kg/L)
- grams per millilitre (g/mL)
- metric tons per cubic metre (t/m3)
Densities using the following metric units all have exactly the same numerical value, one thousandth of the value in (kg/m3). Liquid water has a density of about 1 kg/dm3, making any of these SI units numerically convenient to use as most solids and liquids have densities between 0.1 and 20 kg/dm3.
- kilograms per cubic decimetre (kg/dm3)
- grams per cubic centimetre (g/cc, gm/cc or g/cm3)
- megagrams per cubic metre (Mg/m3)
In U.S. customary units density can be stated in:
- Avoirdupois ounces per cubic inch (oz/cu in)
- Avoirdupois pounds per cubic inch (lb/cu in)
- pounds per cubic foot (lb/cu ft)
- pounds per cubic yard (lb/cu yd)
- pounds per U.S. liquid gallon (lb/gal)
- pounds per U.S. bushel (lb/bu)
- slugs per cubic foot
In principle there are Imperial units different from the above as the Imperial gallon and bushel differ from the U.S. units, but in practice they are no longer used, though found in older documents. The density of precious metals could conceivably be based on Troy ounces and pounds, a possible cause of confusion.
See also
References
- ^ "Density definition in Oil Gas Glossary". Oilgasglossary.com. http://oilgasglossary.com/density.html. Retrieved 2010-09-14.
- ^ Archimedes, A Gold Thief and Buoyancy – by Larry "Harris" Taylor, Ph.D.
- ^ Vitruvius on Architecture, Book IX, paragraphs 9–12, translated into English and in the original Latin.
- ^ The first Eureka moment, Science 305: 1219, August 2004.
- ^ Fact or Fiction?: Archimedes Coined the Term "Eureka!" in the Bath, Scientific American, December 2006.
- ^ a b "Re: which is more bouyant [sic] styrofoam or cork". Madsci.org. http://www.madsci.org/posts/archives/mar2000/954534602.Ph.r.html. Retrieved 2010-09-14.
- ^ CRC Press Handbook of tables for Applied Engineering Science, 2nd Edition, 1976, Table 1-59
- ^ glycerol composition at physics.nist.gov
- ^ Extreme Stars: White Dwarfs & Neutron Stars, Jennifer Johnson, lecture notes, Astronomy 162, Ohio State University. Accessed on line May 3, 2007.
- ^ Nuclear Size and Density, HyperPhysics, Georgia State University. Accessed on line June 26, 2009.
External links
- Video: Density Experiment with Oil and Alcohol
- Video: Density Experiment with Whiskey and Water
- Glass Density Calculation – Calculation of the density of glass at room temperature and of glass melts at 1000 – 1400°C
- List of Elements of the Periodic Table – Sorted by Density
- Calculation of saturated liquid densities for some components
- field density test
- On-line calculator for densities and partial molar volumes of aqueous solutions of some common electrolytes and their mixtures, at temperatures up to 323.15 K.
- Water – Density and Specific Weight
- Temperature dependence of the density of water – Conversions of density units
- A delicious density experiment
- Water density calculator Water density for a given salinity and temperature.
- Liquid density calculator Select a liquid from the list and calculate density as a function of temperature.
- Gas density calculator Calculate density of a gas for as a function of temperature and pressure.
- Densities of various materials.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
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Density
Dansk (Danish)
n. - kompakthed, tæthed, dumhed, vægtfylde, massefylde, optisk tæthed, lydabsorption
Nederlands (Dutch)
dichtheid, bevolkingsdichtheid, compactheid
Français (French)
n. - (Comput) densité, épaisseur (du brouillard), densité (de la population)
Ελληνική (Greek)
n. - πυκνότητα, (μτφ.) βλακεία, χοντροκεφαλιά
Português (Portuguese)
n. - densidade (f)
Русский (Russian)
плотность, густота
Español (Spanish)
n. - densidad, estupidez, densidad de población, grado de opacidad de una substancia, cantidad de información almacenada
Svenska (Swedish)
n. - densitet, täthet
中文（简体）(Chinese (Simplified))
密度
中文（繁體）(Chinese (Traditional))
n. - 密度
日本語 (Japanese)
n. - 密集, 密度, 比重, 頭の悪さ, 濃度
العربيه (Arabic)
(الاسم) كثافه, سعه, العلاقه بين الوزن والحجم ( في الفيزياء)
עברית (Hebrew)
n. - צפיפות, דחיסות, אטימות של צילום, טיפשות (מדוברת)
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