User:Anthony Argyriou/sandbox: Difference between revisions

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In science, energy is a measurable property of a physical or chemical system, which means that the energy of a system may be expressed by a single  real number, say ''A''. It is possible and meaningful to state that the energy of a certain system is equal to ''A'' [[joule]], with joule being an [[SI]] unit for amount of energy.
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'''Energy''' is a scalar property of physical systems, measured in units with dimensions M&sdot;L<sup>2</sup>&sdot;T<sup>-2</sup>.  Energy occurs in several forms; these are [[potential energy]], [[kinetic energy]], [[electromagnetic radiation]], and, according to Einstein's [[special relativity]], [[mass-energy]].  Some forms of kinetic energy (such as [[thermal energy]]) are often treated separately, because of the historic circumstances of their discovery, and for convenience. One fundamental law of physics is that [[Law of conservation of energy|energy is conserved]] - it can change in form, but the total energy of a closed system cannot change, and the energy coming into an open system must equal the energy leaving the system.


Roughly speaking, the energy of a system is a measure of the amount of work that the system is able to perform on its environment. However, the second law of [[thermodynamics]] expresses that some kinds of  energy cannot be converted into work and hence this definition is not completely general and must be handled with care. An additional difficulty in defining energy is that energy has many, seemingly very different, manifestations; be it chemical energy of  a certain amount of [[gasoline]], the kinetic energy of a moving cannon ball, the heat stored in a steam boiler,  the potential energy of water in a reservoir, the nuclear fusion energy contained in a hydrogen bomb, the electricity in a battery, etc. All these manifestations obey the same extremely important law: energy is conserved in conversion from one form of energy to the other. This ''law of conservation of energy'' is known as the first law of thermodynamics. This law pervades all of science, and is probably science's most important principle.
The dimensions of energy correspond to the application of a force over a distance. '''Potential energy''' represents the potential for this to occur, as in the potential of an object to fall in a gravitational field, where the potential is for the force of gravity to be applied to the object over the distance which in can fall. '''Kinetic energy''' is the energy of motion, and is equal to ½mv², where ''m'' is the mass of the object, and ''v'' is the velocity. [[Special relativity]] shows that mass can be converted to energy, and that the energy of mass at rest is equal to mc², where ''c'' is the [[speed of light]]. Special relativity also shows that kinetic energy increases with velocity faster than predicted by Newtonian physics; that additional energy increment is considered to increase the mass of the moving object, as described by the [[Lorentz equations]].


The concept of energy is best explained by means of examples. Assume, to that end, that we use a pump, running on gasoline, to pump water up to a reservoir, and when the reservoir is filled, we let the water flow down to drive an electrical generator. Doing this, we convert  the chemical energy of the gasoline to (i) the mechanical energy of the pump to (ii) the potential energy of the water in the reservoir to  (iii) the kinetic energy of the falling water, and finally to (iv) the electric energy generated by the generator.
[[Electromagnetic radiation]] is also a form of energy ... (There needs to be more here, but I'm running out of steam to write this section.)
If we use the generated electric current for lighting, then the [[light bulb]]s convert the electric current to yet another form of energy, namely (v) [[light]] ([[electromagnetic radiation]]).
 
During these energy conversion processes, the law of conservation of energy assures us that ''no energy is lost''. To  non-scientists  the contrary may seem the case sometimes, because  heat is generated (especially in burning the gasoline to drive the pump), and the heat will escape to the environment without any useful, or directly noticeable, effect. However, since heat is also a form of energy, it must be included in the energy balance of the first law.
The [[SI]] unit of energy is the [[joule (unit)]].

Latest revision as of 01:52, 22 November 2023


The account of this former contributor was not re-activated after the server upgrade of March 2022.


Energy is a scalar property of physical systems, measured in units with dimensions M⋅L2⋅T-2. Energy occurs in several forms; these are potential energy, kinetic energy, electromagnetic radiation, and, according to Einstein's special relativity, mass-energy. Some forms of kinetic energy (such as thermal energy) are often treated separately, because of the historic circumstances of their discovery, and for convenience. One fundamental law of physics is that energy is conserved - it can change in form, but the total energy of a closed system cannot change, and the energy coming into an open system must equal the energy leaving the system.

The dimensions of energy correspond to the application of a force over a distance. Potential energy represents the potential for this to occur, as in the potential of an object to fall in a gravitational field, where the potential is for the force of gravity to be applied to the object over the distance which in can fall. Kinetic energy is the energy of motion, and is equal to ½mv², where m is the mass of the object, and v is the velocity. Special relativity shows that mass can be converted to energy, and that the energy of mass at rest is equal to mc², where c is the speed of light. Special relativity also shows that kinetic energy increases with velocity faster than predicted by Newtonian physics; that additional energy increment is considered to increase the mass of the moving object, as described by the Lorentz equations.

Electromagnetic radiation is also a form of energy ... (There needs to be more here, but I'm running out of steam to write this section.)

The SI unit of energy is the joule (unit).

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