Sketch of gravitational accelerations for two different situations. The panels show a massive body (blue dot) orbiting among stars, and the system’s barycentre at the bottom is the focus of the global gravitational acceleration g_cm (open circle). The mean field acceleration gives rise to a velocity component δv_• along the vertical y-axis. In panel (a), a massive perturber moves at some velocity v_• in an isotropic field of stars; the result of the polarisation of the stellar orbits is a net dynamical friction force a_∥, parallel but in the opposite sense to v_•. In panel (b), the massive body is ejected from the origin at a velocity δv_• pointing upwards. It orbits in a strongly anisotropic (rotating) stellar field and slows down due to the steady negative acceleration g_cm. However, dynamical friction now contributes two terms, one a_∥ as before, and a second one, a_⊥, orthogonal to δv_•. That non-zero component due to the streaming stars causes a steady transfer of angular momentum to the perturber. We refer to this second component as dynamical traction acting on the perturber.