User:Anthony Argyriou/sandbox
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).
- Anthony, after some reflection I have chosen Milton's intro, because it is less technical and more readable for the lay-person. I added at the end of the intro a sentence which basically is your first sentence.
- Further, I want to add that the following sentence is bordering on being wrong:
- Some forms of kinetic energy (such as thermal energy) are often treated separately, because of the historic circumstances of their discovery, and for convenience.
- The term "thermal energy" is ill-defined and hardly ever used. Energy flow is called heat and can take many forms, radiation, transport of potential energy, and also transport of kinetic energy. The fact that "thermal energy" is treated differently is not because of historic circumstance or convenience (in science such reasons do not count and would be soon cut out of textbooks). The reason is that because of the second law of thermodynamics, heat can only be converted partially into work, as discovered by Carnot, Clausius, and Lord Kelvin. I mentioned this several times, and I get the impression that the argument doesn't register with you. Have you ever learned something about the second law?
--Paul Wormer 04:31, 27 July 2008 (CDT)