Frictionless surface, spring at natural length (5 m) at t = 0. Total momentum m1·v1 + m2·v2 stays constant. The ground is fixed (ticks every 1 m) and the blocks move over it; the view is scaled so the whole motion fits. Compression = natural length − current length. The animation runs in slow motion (4× slower) and stops after one oscillation period T = 2π√(μ/k), μ = m1·m2/(m1+m2); the graphs cover exactly that period.