Goodman, Bernard Department of Physics, University of Cincinnati, Cincinnati, Ohio.
Last reviewed:August 2021
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- Least-action principles
- Action variables
- Simple mechanical oscillator
- Charged particle in magnetic field
- Use in old quantum theory
- Significance in quantum mechanics
- Semiclassical approximation
- WKB approximation
- Related Primary Literature
- Additional Reading
Any one of a number of related integral quantities which serve as the basis for general formulations of the dynamics of both classical and quantum-mechanical systems. The term "action" has been associated with four quantities: the fundamental action S, for general paths of a dynamical system; the classical action SC, for the actual path; the modified action S′, for paths restricted to a particular energy; and action variables, for periodic motions. See also: Classical mechanics; Motion; Quantum mechanics
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