Distribution of the change in the average radial random kinetic energy, Δ⟨Π_R⟩(x, y, t) (see Eq. (8)), calculated in the face-on projection ((x, y)-plane) at different times for the thin- (left panels), thick- (middle panels), and thin+thick disc particles (right panels) for model rthickE0.5. The dotted lines denote the contours of the total (thin+thick) surface density. The dashed black circle in each sub-panel denotes the extent of the bar.