We introduced concept of force in describing spin-orbit torque (SOT) inspin-orbit coupling systems. We showed that the damping-like torque is inducedwhen the system is not in steady state, i.e., when the electron spin is stillprecessing ($d{\bf s}/dt\ne 0$) and the electron being accelerated by, e.g., anelectric field. The damping-like SOT can be expressed as ${\bfT}^\mathrm{SO}=({\bf R}\times {\bf F}^{{\mathrm {SO}}})$, which is similar tothe torque-force relation in classical mechanics, where ${\bfF}^{{\mathrm{\mathrm {SO}}}}$ is the spin-force acting on electron, and ${\bfR}\propto \hat{{\bf z}}$ is some effective radius vector. Furthermore, we alsodemonstrated that under the damping SOT, the magnetic energy is transferred toconduction electrons, which dissipates into Joule heating at a rate of $({\bfj}_e\cdot {\bf F}^{\mathrm {SO}})/e$, with $j_e$ being the applied current.Finally, we propose an experimental verification of our findings viameasurement of the anisotropic magnetoresistance effect.
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