Contribution of the different processes to the damping (solid line) and the excitation (dashed line) of the spinning dust emission for a grain with a radius of 3.5  illuminated by the standard ISRF with G₀ = 1. The contributions are normalized to the drag produced by non-elastic collisions in a pure H i gas of a density n_H (Draine & Lazarian 1998). The red lines show the contribution of IR emission, the green lines of collisions with neutrals, the blue lines of collisions with ions, the black lines of plasma drag, the magenta line of photoelectric effect, and the yellow line of H₂ formation.