Density (disambiguation)
Encyclopedia
Density and dense usually refer to a measure of how much of some entity is within a fixed amount of space. Types of density include:
In physics, density of mass
:
In physics, densities of entities other than mass:
In mathematics:
In other scientific fields:
Density can also refer to:
In physics, density of mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
:
- DensityDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, mass per volume - Area density or surface density, mass over a (two-dimensional) area
- Linear densityLinear densityLinear density, linear mass density or linear mass is a measure of mass per unit of length, and it is a characteristic of strings or other one-dimensional objects. The SI unit of linear density is the kilogram per metre...
, mass over a (one-dimensional) line - Bulk densityBulk densityBulk density is a property of powders, granules and other "divided" solids, especially used in reference to mineral components , chemical substances, ingredients, foodstuff or any other masses of corpuscular or particulate matter. It is defined as the mass of many particles of the material...
, mass of many particles of a particulate solid or a powder divided by the total volume they occupy - Particle densityParticle densityThe particle density or true density of a particulate solid or powder, is the density of the particles that make up the powder, in contrast to the bulk density, which measures the average density of a large volume of the powder in a specific medium .The particle density is a relatively well-defined...
or true density, density of the particles that make up a particulate solid or a powder - Relative densityRelative densityRelative density, or specific gravity, is the ratio of the density of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water...
or specific gravitySpecific gravitySpecific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
, a measure of density in comparison to the density of something else- Vapour densityVapour densityVapour density is the density of a vapour in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen....
, a relative density used for gases
- Vapour density
- Planck density, Planck mass per Planck length
In physics, densities of entities other than mass:
- Number densityNumber densityIn physics, astronomy, and chemistry, number density is an intensive quantity used to describe the degree of concentration of countable objects in the three-dimensional physical space...
, number of particles per unit volume, area, or length - Current densityCurrent densityCurrent density is a measure of the density of flow of a conserved charge. Usually the charge is the electric charge, in which case the associated current density is the electric current per unit area of cross section, but the term current density can also be applied to other conserved...
, the ratio of electric current to area - Charge densityCharge densityThe linear, surface, or volume charge density is the amount of electric charge in a line, surface, or volume, respectively. It is measured in coulombs per meter , square meter , or cubic meter , respectively, and represented by the lowercase Greek letter Rho . Since there are positive as well as...
, the electric charge per volume - Energy densityEnergy densityEnergy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
, potential energy per unit volume or mass, depending on context - Force densityForce densityIn fluid mechanics, the force density is the negative gradient of pressure. It has the physical dimensions of force per unit volume. Force density is a vector field representing the flux density of the hydrostatic force within the bulk of a fluid...
, force per unit volume - Optical density, the absorbance of an element
In mathematics:
- Dense setDense setIn topology and related areas of mathematics, a subset A of a topological space X is called dense if any point x in X belongs to A or is a limit point of A...
and nowhere dense setNowhere dense setIn mathematics, a nowhere dense set in a topological space is a set whose closure has empty interior. The order of operations is important. For example, the set of rational numbers, as a subset of R has the property that the closure of the interior is empty, but it is not nowhere dense; in fact it...
in topology - DensityDense setIn topology and related areas of mathematics, a subset A of a topological space X is called dense if any point x in X belongs to A or is a limit point of A...
of a topological space - Schnirelmann densitySchnirelmann densityIn additive number theory, the Schnirelmann density of a sequence of numbers is a way to measure how "dense" the sequence is. It is named after Russian mathematician L.G...
in number theory - Natural densityNatural densityIn number theory, asymptotic density is one of the possibilities to measure how large a subset of the set of natural numbers is....
(also called asymptotic density) in number theory - Lebesgue's density theoremLebesgue's density theoremIn mathematics, Lebesgue's density theorem states that for any Lebesgue measurable set A, the "density" of A is 1 at almost every point in A...
in measure theory - Probability density functionProbability density functionIn probability theory, a probability density function , or density of a continuous random variable is a function that describes the relative likelihood for this random variable to occur at a given point. The probability for the random variable to fall within a particular region is given by the...
, a function which maps probabilities across the real line and whose integral is 1- Density estimationDensity estimationIn probability and statistics,density estimation is the construction of an estimate, based on observed data, of an unobservable underlying probability density function...
is the construction of an estimate of a probability density function - Kernel density estimationKernel density estimationIn statistics, kernel density estimation is a non-parametric way of estimating the probability density function of a random variable. Kernel density estimation is a fundamental data smoothing problem where inferences about the population are made, based on a finite data sample...
, used in statistics to estimate a probability density function of a random variable
- Density estimation
- Tensor densityTensor densityIn differential geometry, a tensor density or relative tensor is a generalization of the tensor concept. A tensor density transforms as a tensor when passing from one coordinate system to another , except that it is additionally multiplied or weighted by a power of the Jacobian determinant of the...
in differential geometry - DensityDense graphIn mathematics, a dense graph is a graph in which the number of edges is close to the maximal number of edges. The opposite, a graph with only a few edges, is a sparse graph...
in graph theory, the fraction of possible edges that exist in a graph - Dense-in-itselfDense-in-itselfIn mathematics, a subset A of a topological space is said to be dense-in-itself if A contains no isolated points.Every dense-in-itself closed set is perfect. Conversely, every perfect set is dense-in-itself....
, in geometry, is a set that contains no isolated points - Dense orderDense orderIn mathematics, a partial order ≤ on a set X is said to be dense if, for all x and y in X for which x In mathematics, a partial order ≤ on a set X is said to be dense if, for all x and y in X for which x...
in order theory - DenseForcing (mathematics)In the mathematical discipline of set theory, forcing is a technique invented by Paul Cohen for proving consistency and independence results. It was first used, in 1963, to prove the independence of the axiom of choice and the continuum hypothesis from Zermelo–Fraenkel set theory...
can used to refer to a coinitialCofinal (mathematics)In mathematics, let A be a set and let ≤ be a binary relation on A. Then a subset B of A is said to be cofinal if it satisfies the following condition:This definition is most commonly applied when A is a partially ordered set or directed set under the relation ≤. Also, the notion of cofinal...
subset in the theory of forcingForcing (mathematics)In the mathematical discipline of set theory, forcing is a technique invented by Paul Cohen for proving consistency and independence results. It was first used, in 1963, to prove the independence of the axiom of choice and the continuum hypothesis from Zermelo–Fraenkel set theory...
. - Density of a polytopePolytope densityIn geometry, polytope density represents the number of windings of a polytope, particularly a uniform or regular polytope, around its center. It can be visually determined by counting the minimum number of facet crossings of a ray from the center to infinity...
in geometry - Density on a manifoldDensity on a manifoldIn mathematics, and specifically differential geometry, a density is a spatially varying quantity on a differentiable manifold which can be integrated in an intrinsic manner. Abstractly, a density is a section of a certain trivial line bundle, called the density bundle...
- Dense submoduleDense submoduleIn abstract algebra, specifically in module theory, a dense submodule of a module is a refinement of the notion of an essential submodule. If N is a dense submodule of M, it may also be said it may alternatively be said that "N ⊆ M is a rational extension". Dense submodules are connected...
in abstract algebra
In other scientific fields:
- Population densityPopulation densityPopulation density is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, and particularly to humans...
, population per unit area - Memory storage density, bits (how computers store information) over an amount of area or volume
Density can also refer to:
- Plane (esotericism)Plane (esotericism)In esoteric cosmology, a plane, other than the physical plane is conceived as a subtle state of consciousness that transcends the known physical universe....
(spiritual density), states of being for various planes of existence - StupidityStupidityStupidity is a lack of intelligence, understanding, reason, wit, or sense. It may be innate, assumed, or reactive - 'being "stupid with grief" as a defence against trauma', a state marked with 'grief and despair...making even simple daily tasks a hardship'....
, a stupid person is sometimes referred to as being "dense"