= Solution
Use a local Cartesian frame rotating at $\Omega=\sqrt{GM/r_0^3}$ about a circular orbit at $r_0$, with $x=r-r_0\ll r_0$, and neglect curvature beyond leading order. The radial gravitational-plus-centrifugal potential is
$$
\Phi_{\rm eff}(r)=-\frac{GM}{r}-\frac12\Omega^2r^2.
$$
Its first derivative vanishes at $r_0$ and its second derivative there is $-3\Omega^2$. Dropping a constant gives the <shearing-sheet tidal potential>
$$
\boxed{\Phi_t=-\frac32\Omega^2x^2}.
$$
Back to article page
