Theorem 5 (Nonholonomic constraints) For nonholonomic constraints linear in velocities (distribution D ⊂ TQ), the Lagrange–d'Alembert principle yields constrained equations; these do not in general derive from a variational principle on reduced space. Well-posedness is proved under standard regularity and complementarity conditions (Section 6).
Theorem 3 (Hamiltonian formulation and symplectic structure) T Q is a symplectic manifold with canonical 2-form ω_can. For Hamiltonian H: T Q → R, integral curves of the Hamiltonian vector field X_H satisfy Hamilton's equations; flow preserves ω_can and H. For rigid bodies on SO(3), passing to body angular momentum π = I ω yields Lie–Poisson equations: π̇ = π × I^{-1} π + external torques (Section 4–5). rigid dynamics krishna series pdf
Theorem 4 (Reduction by symmetry — Euler–Poincaré) If L is invariant under a Lie group G action, then dynamics reduce to the Lie algebra via the Euler–Poincaré equations. For rigid body with G = SO(3), reduced equations are Euler's equations. (Proof: Section 7.) For Hamiltonian H: T Q → R, integral
Theorem 6 (Structure-preserving integrators) Lie group variational integrators constructed via discrete variational principles on G (e.g., discrete Lagrangian on SE(3)) produce discrete flows that preserve group structure and a discrete momentum map; they exhibit good long-term energy behavior. Convergence and order results are stated and proven for schemes of practical interest (Section 9). For rigid body with G = SO(3), reduced
Abstract A self-contained, rigorous treatment of rigid-body dynamics is presented, unifying classical formulations (Newton–Euler, Lagrange, Hamilton) with modern geometric mechanics (Lie groups, momentum maps, reduction, symplectic structure). The monograph develops kinematics, equations of motion, variational principles, constraints, stability and conservation laws, and computational techniques for simulation and control. Emphasis is placed on mathematical rigor: precise definitions, well-posedness results, coordinate-free formulations on SE(3) and SO(3), and proofs of equivalence between formulations.
Theorem 1 (Newton–Euler Equations, body frame) Let a rigid body of mass m and inertia I (in body frame) move in space under external force F_ext and moment M_ext expressed in body coordinates. The equations of motion in body frame are: m (v̇ + ω × v) = F_body I ω̇ + ω × I ω = M_body where v is body-frame linear velocity of the center of mass, ω is body angular velocity. (Proof: Section 3.)
