# Goldstein Central Force Repulsive Scattering

1. Jul 17, 2015

### decerto

On page 108 in Goldstein 3rd edition in the paragraph after equation (3.94) he says that $\psi$` can be obtained from the orbit equation (3.36) using the limits as $r_0=\infty$ $r=r_m$ which the distance of closest approach and $\theta_0=\pi$ which is the initial direction.

So looking at the diagram on the top of the page this angle he is calculating $\theta$ seems to me to be exactly $\psi$ but he says that $\psi=\pi-\theta$

When we start at $r=\infty , \theta = \pi$ and move to $r=r_m$ on the diagram the corresponding angle traced out is $\theta=\psi$ where am I going wrong/

The book is here for anyone who doesnt have it.

Last edited by a moderator: May 7, 2017
2. Jul 19, 2015

### Staff: Mentor

You start out at an angle of $\pi$ and trace out an angle $\psi$ so you must end up at an angle $\pi-\psi$.