On pages112 and 112c we use the centripetal acceleration of planets to discover the inverse-square gravitation law. On pages 113 and 113b we figure out the rest of Newton’s universal gravitation law, including the proportionality constant. On pages 114 and 114b there are some exercises to help students get used to the new law. On pages 115 and 115b we figure out how gravitational potential energies can be determined in an inverse-square law field. On pages 116 and 116R we explore the similarities between electric and gravitational fields, leading to Coulomb’s law. (116R is about the wonderful PSSC film by Eric Rogers about Coulomb’s law.) On pages 117 and 118 we use compasses to map magnetic dipole fields and then figure out what simple gravitational and electric field maps must look like. On pages 119 and 119b we figure out some new electric field formulas.