Linearisation around equilibrium: the quadratic Lagrangian ½(M ẋ·ẋ − K x·x) diagonalises in normal modes x_k = a_k cos(ω_k t + φ_k).
Linearisation around equilibrium: the quadratic Lagrangian ½(M ẋ·ẋ − K x·x) diagonalises in normal modes x_k = a_k cos(ω_k t + φ_k).