Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains. Volume is often quantified numerically using the SI derived unit, the cubic metre. The volume of a container is generally understood to be the capacity of the container; i.e., the amount of fluid (gas or liquid) that the container could hold, rather than the amount of space the container itself displaces. Three dimensional mathematical shapes are also assigned volumes. Volumes of some simple shapes, such as regular, straight-edged, and circular shapes can be easily calculated using arithmetic formulas. Volumes of complicated shapes can be calculated with integral calculus if a formula exists for the shape's boundary. One-dimensional figures (such as lines) and two-dimensional shapes (such as squares) are assigned zero volume in the three-dimensional space. The volume of a solid (whether regularly or irregularly shaped) can be determined by fluid displacement. Displacement of liquid can also be used to determine the volume of a gas. The combined volume of two substances is usually greater than the volume of just one of the substances. However, sometimes one substance dissolves in the other and in such cases the combined volume is not additive. In ''differential geometry'', volume is expressed by means of the volume form, and is an important global Riemannian invariant. In ''thermodynamics'', volume is a fundamental parameter, and is a conjugate variable to pressure.

Units

Any unit of length gives a corresponding unit of volume: the volume of a cube whose sides have the given length. For example, a cubic centimetre (cm³) is the volume of a cube whose sides are one centimetre (1 cm) in length. In the International System of Units (SI), the standard unit of volume is the cubic metre (m³). The metric system also includes the litre (L) as a unit of volume, where one litre is the volume of a 10-centimetre cube. Thus :1 litre = (10 cm)³ = 1000 cubic centimetres = 0.001 cubic metres, so :1 cubic metre = 1000 litres. Small amounts of liquid are often measured in millilitres, where :1 millilitre = 0.001 litres = 1 cubic centimetre. In the same way, large amounts can be measured in megalitres, where :1 million litres = 1000 cubic metres = 1 megalitre. Various other traditional units of volume are also in use, including the cubic inch, the cubic foot, the cubic yard, the cubic mile, the teaspoon, the tablespoon, the fluid ounce, the fluid dram, the gill, the pint, the quart, the gallon, the minim, the barrel, the cord, the peck, the bushel, the hogshead, the acre-foot and the board foot.


Related terms

''Capacity'' is defined by the Oxford English Dictionary as "the measure applied to the content of a vessel, and to liquids, grain, or the like, which take the shape of that which holds them". (The word ''capacity'' has other unrelated meanings, as in e.g. capacity management.) Capacity is not identical in meaning to volume, though closely related; the capacity of a container is always the volume in its interior. Units of capacity are the SI litre and its derived units, and Imperial units such as gill, pint, gallon, and others. Units of volume are the cubes of units of length. In SI the units of volume and capacity are closely related: one litre is exactly 1 cubic decimetre, the capacity of a cube with a 10 cm side. In other systems the conversion is not trivial; the capacity of a vehicle's fuel tank is rarely stated in cubic feet, for example, but in gallons (an imperial gallon fills a volume with 0.1605 cu ft). The ''density'' of an object is defined as the ratio of the mass to the volume. The inverse of density is ''specific volume'' which is defined as volume divided by mass. Specific volume is a concept important in thermodynamics where the volume of a working fluid is often an important parameter of a system being studied. The volumetric flow rate in fluid dynamics is the volume of fluid which passes through a given surface per unit time (for example cubic meters per second ³ s⁻¹.


Volume in calculus

In calculus, a branch of mathematics, the volume of a region ''D'' in R³ is given by a triple integral of the constant function $f(x,y,z)=1$ over the region and is usually written as: :$\backslash iiint\backslash limits\_D\; 1\; \backslash ,dx\backslash ,dy\backslash ,dz.$ In cylindrical coordinates, the volume integral is :$\backslash iiint\backslash limits\_D\; r\backslash ,dr\backslash ,d\backslash theta\backslash ,dz,$ In spherical coordinates (using the convention for angles with $\backslash theta$ as the azimuth and $\backslash varphi$ measured from the polar axis; see more on conventions), the volume integral is :$\backslash iiint\backslash limits\_D\; \backslash rho^2\; \backslash sin\backslash varphi\; \backslash ,d\backslash rho\; \backslash ,d\backslash theta\backslash ,\; d\backslash varphi\; .$


Volume formulas



Volume ratios for a cone, sphere and cylinder of the same radius and height

The above formulas can be used to show that the volumes of a cone, sphere and cylinder of the same radius and height are in the ratio 1 : 2 : 3, as follows. Let the radius be ''r'' and the height be ''h'' (which is 2''r'' for the sphere), then the volume of the cone is :$\backslash frac\; \backslash pi\; r^2\; h\; =\; \backslash frac\; \backslash pi\; r^2\; \backslash left(2r\backslash right)\; =\; \backslash left(\backslash frac\; \backslash pi\; r^3\backslash right)\; \backslash times\; 1,$ the volume of the sphere is :$\backslash frac\; \backslash pi\; r^3\; =\; \backslash left(\backslash frac\; \backslash pi\; r^3\backslash right)\; \backslash times\; 2,$ while the volume of the cylinder is :$\backslash pi\; r^2\; h\; =\; \backslash pi\; r^2\; (2r)\; =\; \backslash left(\backslash frac\; \backslash pi\; r^3\backslash right)\; \backslash times\; 3.$ The discovery of the 2 : 3 ratio of the volumes of the sphere and cylinder is credited to Archimedes.


Volume formula derivations




Sphere

The volume of a sphere is the integral of an infinite number of infinitesimally small circular disks of thickness ''dx''. The calculation for the volume of a sphere with center 0 and radius ''r'' is as follows. The surface area of the circular disk is $\backslash pi\; r^2$. The radius of the circular disks, defined such that the x-axis cuts perpendicularly through them, is : $y\; =\; \backslash sqrt$ or : $z\; =\; \backslash sqrt$ where y or z can be taken to represent the radius of a disk at a particular x value. Using y as the disk radius, the volume of the sphere can be calculated as : $\backslash int\_^r\; \backslash pi\; y^2\; \backslash ,dx\; =\; \backslash int\_^r\; \backslash pi\backslash left(r^2\; -\; x^2\backslash right)\; \backslash ,dx.$ Now : $\backslash int\_^r\; \backslash pi\; r^2\backslash ,dx\; -\; \backslash int\_^r\; \backslash pi\; x^2\backslash ,dx\; =\; \backslash pi\; \backslash left(r^3\; +\; r^3\backslash right)\; -\; \backslash frac\backslash left(r^3\; +\; r^3\backslash right)\; =\; 2\backslash pi\; r^3\; -\; \backslash frac.$ Combining yields $V\; =\; \backslash frac\backslash pi\; r^3.$ This formula can be derived more quickly using the formula for the sphere's surface area, which is $4\backslash pi\; r^2$. The volume of the sphere consists of layers of infinitesimally thin spherical shells, and the sphere volume is equal to : $\backslash int\_0^r\; 4\backslash pi\; r^2\; \backslash ,dr\; =\; \backslash frac\backslash pi\; r^3.$


Cone

The cone is a type of pyramidal shape. The fundamental equation for pyramids, one-third times base times altitude, applies to cones as well. However, using calculus, the volume of a cone is the integral of an infinite number of infinitesimally thin circular disks of thickness ''dx''. The calculation for the volume of a cone of height ''h'', whose base is centered at (0, 0, 0) with radius ''r'', is as follows. The radius of each circular disk is ''r'' if ''x'' = 0 and 0 if ''x'' = ''h'', and varying linearly in between—that is, : $r\; \backslash frac.$ The surface area of the circular disk is then : $\backslash pi\; \backslash left(r\backslash frac\backslash right)^2\; =\; \backslash pi\; r^2\backslash frac.$ The volume of the cone can then be calculated as : $\backslash int\_0^h\; \backslash pi\; r^2\backslash frac\; dx,$ and after extraction of the constants : $\backslash frac\; \backslash int\_0^h\; (h\; -\; x)^2\; dx$ Integrating gives us : $\backslash frac\backslash left(\backslash frac\backslash right)\; =\; \backslash frac\backslash pi\; r^2\; h.$


Polyhedron




Volume in differential geometry

In differential geometry, a branch of mathematics, a volume form on a differentiable manifold is a differential form of top degree (i.e., whose degree is equal to the dimension of the manifold) that is nowhere equal to zero. A manifold has a volume form if and only if it is orientable. An orientable manifold has infinitely many volume forms, since multiplying a volume form by a non-vanishing function yields another volume form. On non-orientable manifolds, one may instead define the weaker notion of a density. Integrating the volume form gives the volume of the manifold according to that form. An oriented pseudo-Riemannian manifold has a natural volume form. In local coordinates, it can be expressed as :$\backslash omega\; =\; \backslash sqrt\; \backslash ,\; dx^1\; \backslash wedge\; \backslash dots\; \backslash wedge\; dx^n\; ,$ where the $dx^i$ are 1-forms that form a positively oriented basis for the cotangent bundle of the manifold, and $g$ is the determinant of the matrix representation of the metric tensor on the manifold in terms of the same basis.


Volume in thermodynamics

In thermodynamics, the volume of a system is an important extensive parameter for describing its thermodynamic state. The specific volume, an intensive property, is the system's volume per unit of mass. Volume is a function of state and is interdependent with other thermodynamic properties such as pressure and temperature. For example, volume is related to the pressure and temperature of an ideal gas by the ideal gas law.


Volume computation

The task of numerically computing the volume of objects is studied in the field of computational geometry in computer science, investigating efficient algorithms to perform this computation, approximately or exactly, for various types of objects. For instance, the convex volume approximation technique shows how to approximate the volume of any convex body using a membership oracle.


See also



References



External links

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