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In physics, potential energy is the energy that an object has due to its position in a force field or that a system has due to the configuration of its parts. Common types include the gravitational potential energy of an object that depends on its mass and its distance from the center of mass of another object, the elastic potential energy of an extended spring, and the electric potential energy of a electric charge in an electric field. The unit for energy in the International System of Units (SI) is the joule, which has the symbol ''J''. The term ''potential energy'' was introduced by the 19th century Scottish engineer and physicist William Rankine,〔William John Macquorn Rankine (1853) "On the general law of the transformation of energy," ''Proceedings of the Philosophical Society of Glasgow'', vol. 3, no. 5, pages 276-280; reprinted in: (1) ''Philosophical Magazine'', series 4, vol. 5, no. 30, (pages 106-117 ) (February 1853); and (2) W. J. Millar, ed., ''Miscellaneous Scientific Papers: by W. J. Macquorn Rankine'', ... (London, England: Charles Griffin and Co., 1881), part II, (pages 203-208 ).〕 although it has links to Greek philosopher Aristotle's concept of potentiality. Potential energy is associated with forces that act on a body in a way that depends only on the body's position in space. These forces can be represented by a vector at every point in space forming a vector field of forces, or a force field. If the work of a force field acting on a body that moves from a start to an end position is determined only by these two positions, and does not depend on the trajectory of the body, then there is a function known as ''potential energy'' that can be evaluated at the two positions to determine this work. Furthermore, the force field is determined by this potential energy and is described as derivable from a potential. ==Overview== Potential energy is the stored energy of an object. It is the energy by virtue of an object's position relative to other objects. Potential energy is often associated with restoring forces such as a spring or the force of gravity. The action of stretching the spring or lifting the mass is performed by an external force that works against the force field of the potential. This work is stored in the force field, which is said to be stored as potential energy. If the external force is removed the force field acts on the body to perform the work as it moves the body back to the initial position, reducing the stretch of the spring or causing a body to fall. The more formal definition is that potential energy is the energy difference between the energy of an object in a given position and its energy at a reference position. There are various types of potential energy, each associated with a particular type of force. For example, the work of an elastic force is called elastic potential energy; work of the gravitational force is called gravitational potential energy; work of the Coulomb force is called electric potential energy; work of the strong nuclear force or weak nuclear force acting on the baryon charge is called nuclear potential energy; work of intermolecular forces is called intermolecular potential energy. Chemical potential energy, such as the energy stored in fossil fuels, is the work of the Coulomb force during rearrangement of mutual positions of electrons and nuclei in atoms and molecules. Thermal energy usually has two components: the kinetic energy of random motions of particles and the potential energy of their mutual positions. Forces derivable from a potential are also called conservative forces. The work done by a conservative force is : where is the change in the potential energy associated with the force. The negative sign provides the convention that work done against a force field increases potential energy, while work done by the force field decreases potential energy. Common notations for potential energy are ''U'', ''V'', and ''Ep''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Potential energy」の詳細全文を読む スポンサード リンク
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