# 7: Symmetries, Invariance and the Hamiltonian

- Page ID
- 9606

- 7.1: Introduction to Symmetries, Invariance, and the Hamiltonian
- Chapter 7 will explore the remarkable connection between symmetry and invariance of a system under transformation, and the related conservation laws that imply the existence of constants of motion.

- 7.2: Generalized Momentum
- Introduce generalized momentum.

- 7.3: Invariant Transformations and Noether’s Theorem
- For each symmetry of the Lagrangian there is a conserved quantity.

- 7.4: Rotational invariance and conservation of angular momentum
- Noether’s Theorem illustrates this general result which can be stated as, if the Lagrangian is rotationally invariant about some axis, then the component of the angular momentum along that axis is conserved. Also this is true for the more general case where the Lagrangian is invariant to rotation about any axis, which leads to conservation of the total angular momentum.

- 7.5: Cyclic Coordinates
- A cyclic coordinate is one that does not explicitly appear in the Lagrangian.

- 7.6: Kinetic Energy in Generalized Coordinates
- Application of Noether’s theorem to the conservation of energy requires the kinetic energy to be expressed in generalized coordinates.

- 7.8: Generalized energy theorem
- The Hamiltonian and generalized energy are constants of motion if the Lagrangian is a constant of motion and the external nonpotential forces are zero.

- 7.9: Generalized energy and total energy
- Conservation laws.

- 7.10: Hamiltonian Invariance
- Previously, two important and independent features of the Hamiltonian were addressed: a) when H is conserved, and b) when H equals the total mechanical energy. These important results are summarized below with a discussion of the assumptions made in deriving the Hamiltonian, as well as the implications.

- 7.11: Hamiltonian for Cyclic Coordinates
- Constant of motion.

- 7.12: Symmetries and Invariance
- Symmetries and invariance in classical mechanics.

Thumbnail: Amalie Emmy Noether was a German mathematician known for her landmark contributions to abstract algebra and theoretical physics. She invariably used the name "Emmy Noether" in her life and publications. She was described by Pavel Alexandrov, Albert Einstein, Jean Dieudonné, Hermann Weyl, and Norbert Wiener as the most important woman in the history of mathematics. As one of the leading mathematicians of her time, she developed the theories of rings, fields, and algebras. In physics, Noether's theorem explains the connection between symmetry and conservation laws.