There are a few resources to help you out with this topic. There are the videos below, of course, but there is this SCREENCAST describing gravity inside the Earth, and there is this SCREENCAST on tunneling through the Earth.
Source: Hewitt, P. G. (2015). Conceptual Physics (12th ed.). Boston, MA: Pearson.
Source: HEWITT, P. G. (2015). CONCEPTUAL PHYSICS (12TH ED.). BOSTON, MA: PEARSON.
Source: HEWITT, P. G. (2015). CONCEPTUAL PHYSICS (12TH ED.). BOSTON, MA: PEARSON.
