Impulse approximation
= Impulse approximation
In a rapid encounter, the impulse approximation holds stellar positions fixed while integrating an external acceleration over time. A stellar velocity kick is $\Delta\mathbf v=\int\mathbf a_{\rm tidal}(t)\,dt$. If the encounter time $p/v$ is much shorter than the orbital time $\Omega^{-1}$, this gives reliable leading <tidal heating> for a weak, distant encounter. Slow perturbations require <adiabatic shielding of tidal encounters> instead.