Periodic action–angle variables
For one regular periodic Hamiltonian orbit, I=(1/2π)∮p dq and its conjugate angle θ advances at ω=∂H/∂I; equivalently dI/dE=T/(2π).
Key knowledge
For one regular periodic Hamiltonian orbit, I=(1/2π)∮p dq and its conjugate angle θ advances at ω=∂H/∂I; equivalently dI/dE=T/(2π). The harmonic oscillator has I=E/ω₀. Separable integrable systems extend this construction to independent cycles, whereas generic nonintegrable motion does not.
Values and equations
I=(1/2π)∮p dq; θ̇=ω=∂H/∂I; dI/dE=T/(2π); I_HO=E/ω₀
- I
- Normalized action J s
- p,q
- Canonical momentum/coordinate; product unit J s
- θ
- Conjugate angle rad
- H,E
- Hamiltonian/energy J
- ω,ω₀
- Angular frequencies rad s⁻¹
- T
- Orbit period s
Conditions and scope
- Closed regular cycle or a periodic angular coordinate, smooth locally invertible I(E), finite positive period and away from a separatrix.
- This record uses the 2π-normalized action and angle advancing by 2π. The source uses J=2πI and an angle advancing by one; its cyclic frequency is ∂H/∂J.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Classical Mechanics III 8.09 (2014): Chapter 4: §4.6 printed pages 84–86, equations 4.173–4.179 and 4.186–4.193: cycle integral, frequency and oscillator; normalization explicitly converted.
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Entry details
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- physics-periodic-action-angle
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- university-core.1
- Structured reference record
- University core expansion