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:This article is about the scientific concept. Energy use by humans is discussed in other articles .Energy, generally and qualitatively speaking, is the property (or the quantity of the property) of doing things or supplying power. The expressions energy and power have different meaning in different scientific and non-scientific fields. Physics aims to explain quantitatively this property and gives a definition that makes it possible to consider energy as a description of the whole state and the different ways jobs are done are unified in this treatment.
Energy is a fundamental quantity that every physical system possesses; it allows us to predict how much work the system could be made to do, or how much heat it can exchange. In the past, energy was discussed in terms of easily observable effects it has on the properties of objects or changes in state of various systems. Basically, if something changes, some sort of energy was involved in that change. As it was realized that energy could be stored in objects, the concept of energy came to embrace the idea of the potential for change as well as change itself. Such effects (both potential and realized) come in many different forms; examples are the electrical energy stored in a battery, the chemical energy stored in a piece of food, the thermal energy of a hot water heater, or the kinetic energy of a moving train. To simply say energy is "change or the potential for change", however, misses many important examples of energy as it exists in the physical world. Energy can be used not only to produce observable change, it also is used to prevent change in which case unaided observation of this kind of energy can be difficult. For example, looking at a statue holding a 50 pound weight, the presence of energy needed to do so may not be observable. However, if you are holding up the fifty pound weight instead of the statue the need for energy to accomplish this becomes apparent. You can feel the gravitational force on you both when you are moving the weight up and when you are not moving it. Energy can be readily transformed from one form into another; for instance, using a battery to power an electrical heater converts electrical energy into thermal energy. In the previous example of holding the fifty pount weight, the work you perform to rise the weight is observed as kinetic energy of motion which is converted to potential energy and added to the weight's potential energy as you continue to hold the weight up against the pull of gravity. Letting go of the weight once again transforms this stored potential energy back into kinetic energy as the weight falls under the force of gravity. The law of conservation of energy states that in these conversions the total amount of energy always remains the same. The concept of energy is a powerful tool in physics and, to assure its continued validity, scientists have defined several additional forms of energy that are not easily measured by the unaided observer.
1 Units
1.1 SI and related units
The SI unit for both energy and work is the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat . In slightly more fundamental terms, 1 joule is equal to 1 newton- metreFor other uses of "metre" and "meter", see Metre (disambiguation). The metre is the basic unit of length in the International System of Units (SI: Systeme International d'Unites). It is defined as the length of the path travelled by light in absolute vacu and, in terms of SI base unitThe SI system of units defines seven SI base units fundamental physical units defined by an operational definition. All other physical units can be derived from these base units: these are known as SI derived units. Derivation is by dimensional analysis.s, 1 J is equal to 1 kgThe kilogram (symbol: kg is the SI base unit of mass. A gram is defined as one thousandth of a kilogram. Conversion of units describes equivalent units of mass in other systems. Multiples SI prefixes are used to name multiples and subdivisions of the kilo mFor other uses of "metre" and "meter", see Metre (disambiguation). The metre is the basic unit of length in the International System of Units (SI: Systeme International d'Unites). It is defined as the length of the path travelled by light in absolute vacu2 sThis article is about the unit of time. See second (disambiguation) for other uses The second (symbol s is a unit for time, and one of seven SI base units. It is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transi−2.
An energy unit that is used in particle physicsParticle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. It is also called high energy physics because many elementary particles do not occur under normal circumstances in is the electronvoltAn electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. This is a very small amount of energy: : 1 eV 1. 602 176 53 (14) × 10−19 J. Source: COD (eV). One eV is equivalent to 1.602176462×10−19 JTo help compare different orders of magnitude we list here energies between 10−19 joules and 10−18 joules (0. Weaker energies 1. 602 × 10−19 J 1 electron volt (eV) 1. 602 × 10−19 J Average kinetic energy of a molecule at 11300 ° C.
(Note that torque has the same units as energy, but there is no deeper connection between the two concepts.)
