Grainvelocities (left axis) and Hall factor (right axis) as a function of the grain radius for a gas proton density n_H of 10⁴ cm ⁻³ (left), 10⁶ cm⁻³ (middle) and 10⁸ cm⁻³ (right). The ambipolar diffusion velocity V_AD is fixed and equal to c_s∕10 = 20 m s⁻¹. We present the components V_∥ parallel to the infall (magenta) and V_⊥ perpendicular to the infall and to the magnetic field direction (green). For comparison, the turbulent relative velocities ΔV from Fig. 2 are overplotted in dotted blue lines. The grain specific density is 3 g cm ⁻³.