= Drag dissipation of a bead-spring pair
{title2=$D_{\rm pair}=\zeta|\dot{\mathbf R}-K\mathbf R|^2/2$}
When the midpoint follows a <linear velocity field>, the two beads' slip <velocities> are $\pm(\dot{\mathbf R}-K\mathbf R)/2$. Summing their individual drag powers $\zeta|\mathbf v_{\rm slip}|^2$ proves the displayed expression. Using a <probability current velocity> in place of the instantaneous relative velocity defines the corresponding overdamped dissipative functional; adding independent thermal velocities is a different stochastic description.
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