Restructure: USD fix + updated descendants

# [SCI] Analytical Mechanics

**Analytical Mechanics** is the reformulation of Newtonian mechanics using variational principles and generalised coordinates (Lagrange, 1788; Hamilton, 1833), providing the mathematical tools for all of modern theoretical physics.

## Overview

Joseph-Louis Lagrange replaced Newton's vector forces with a scalar energy function (the Lagrangian L = T − V) and derived equations of motion from the principle of stationary action. William Rowan Hamilton introduced the Hamiltonian formulation (phase space, canonical coordinates), which revealed deep connections between classical mechanics and optics, and later became the direct precursor of quantum mechanics.

These formalisms are not merely mathematical conveniences: Noether's theorem (1915) showed that every continuous symmetry of the Lagrangian corresponds to a conserved quantity (energy ↔ time translation; momentum ↔ space translation; angular momentum ↔ rotation).

## Key Figures & Recognition

- **J.-L. Lagrange** (1736–1813): *Mécanique analytique*, 1788.
- **W. R. Hamilton** (1805–1865): Hamilton's principle, quaternions.
- **Emmy Noether** (1882–1935): Noether's theorem, 1915. No Nobel (women excluded at the time).

## Seminal Papers

- Lagrange, J.-L. *Mécanique analytique*. 1788.
- Hamilton, W.R. "On a General Method in Dynamics." *Phil. Trans. R. Soc.* 124 (1834).
- Noether, E. "Invariante Variationsprobleme." *Nachr. Ges. Wiss. Göttingen* (1918).

## What This Enables

- **[SCI] Special Relativity** — Hamilton's principle and Lorentz-invariant action are the natural mathematical language in whichof SR is formulated.
- **[SCI] Gravitational Wave Theory** — The GR quadrupole radiation formula for radiated power is derived using the Lagrangian field formalism of analytical mechanics.
- **[TECH] Rocket & Space Launch** — Orbital mechanics and, trajectory optimisation, and guidance equations are Hamiltonian mechanics problems.

# Parents

* [SCI] Newtonian Mechanics
* [SCI] Newtonian Mechanics