ⓘ System: m·ẍ + c·ẋ + k·x = 0 (free vibration, ẋ₀ = 0). ωn = √(k/m), ζ = c / (2√(km)).
Eigenvalues s = −ζωn ± ωn√(ζ²−1); ζ<1 underdamped (complex conjugate, oscillatory),
ζ=1 critically damped, ζ>1 overdamped (two real roots). The solution is calculated analytically; the animation is in real-time (1 s = 1 s).
Real eigenvector directions are plotted on the phase portrait when eigenvalues are real.