Active particles in non-inertial frames: how to self-propel on a carousel

Abstract

Typically the motion of self-propelled active particles is described in a quiescent environment establishing an inertial frame of reference. Here we assume that friction, self-propulsion and uctuations occur relative to a non-inertial frame and thereby the active Brownian motion model is generalized to non-inertial frames. First, analytical solutions are presented for the overdamped case, both for linear swimmers and circle swimmers. For a frame rotating with constant angular velocity ("carousel"), the resulting noise-free trajectories in the static laboratory frame trochoids if these are circles in the rotating frame. For systems governed by inertia, such as vibrated granulates or active complex plasmas, centrifugal and Coriolis forces become relevant. For both linear and circling self-propulsion, these forces lead to out-spiraling trajectories which for long times approach a spira mirabilis. This implies that a self-propelled particle will typically leave a rotating carousel. A navigation strategy is proposed to avoid this expulsion, by adjusting the self-propulsion direction at wish. For a particle, initially quiescent in the rotating frame, it is shown that this strategy only works if the initial distance to the rotation centre is smaller than a critical radius Rc which scales with the self-propulsion velocity. Possible experiments to verify the theoretical predictions are discussed.