1. ζA = (R - r).F = dL/dt = d**(m.R² / 2) + m.R²+.ω+/dt
(R - r).F = α.(3.m / 2).R² = 3.a.m.R / 2 (pois α = a / R)
a = (2/3).(R - r).F / R.m = 2.F.(1 - r/R) / 3.m