Dust number distributions at different stages during the collapse. Comparison between different sources of relative velocities with and without fragmentation : TURB (turbulence only), TURB − AD (turbulence plus ambipolar diffusion) and TURB − BR (turbulence plus Brownian motion). The solid lines refer to the purely coagulating cases, while fragmentation is included for the dashed lines (γ_grain = 10 erg cm⁻²).