Fig. 2: Experimental setup: passive tracer in an inertial active bath.
From: Emergent memory from tapping collisions in active granular matter
a, b Photos and diagrams of passive tracer and active vibrobots, respectively. White spots indicate a reference angle for the passive tracer and the orientational angle for active particles. c Photo of the shaker and plate where the motion takes place. d–f Captured images of the passive tracer in a bath of active particles at packing fractions ϕ = 0, 0.15, 0.3, respectively. Here, the white scale bars read 30 mm. Corresponding ~80 s long tracer trajectories are shown in (g–i), with a color gradient denoting the total kinetic energy of the particle \({{{{{{{\mathcal{K}}}}}}}}={{{{{{{{\mathcal{K}}}}}}}}}_{{{{{{{{\rm{t}}}}}}}}}+{{{{{{{{\mathcal{K}}}}}}}}}_{{{{{{{{\rm{r}}}}}}}}}\), given by the sum of the translational and rotational contributions. Trajectories show an emergent memory for the active bath that results in correlated motion. Here, the black scale bars read 55 mm.
