Conservation of energy
Roller, Duane E. Formerly, Harvey Mudd College, Claremont, California.
Nedelsky, Leo Department of Physical Science, University of Chicago, Chicago, Illinois.
Last reviewed:June 2018
Show previous versions
- Application to life processes
- Conservation of mechanical energy
- Mechanical equivalent of heat
- Conservation of mass-energy
- Laws of motion
- Additional Readings
The principle stating that energy cannot be created or destroyed, although it can be changed from one form to another. The law of conservation of energy has been established by a multitude of meticulous measurements of gains and losses of all known forms of energy. Some parts or particles of the system may gain energy, but others must lose just as much. Thus, in any isolated or closed system, the sum of all forms of energy remains constant. The energy of the system may be interconverted among many different forms (see illustration), including mechanical, electrical, magnetic, thermal, chemical, and nuclear forms. Moreover, as time progresses, it tends to become less and less available. However, within the limits of small experimental uncertainty, no change in total amount of energy has been observed in any situation in which it has been possible to ensure that energy has not entered or left the system in the form of work or heat. For a system that is both gaining and losing energy in the form of work and heat, as is true of any machine in operation, the energy principle asserts that the net gain of energy is equal to the total change of the system's internal energy. See also: Conservation laws (physics); Energy; Energy conversion; Thermodynamic principles
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