... 22.Reference Frames . ... Inertial Forces . 23a. The Centrifugal Force . ... When calculating the motions of the oceans and the atmosphere, it is much easier to use reference points on the rotating Earth and add a centrifugal force to all equations. ... The rest arises because the Earth is not a perfect sphere: the centrifugal force of its rotation causes its equator to bulge out , making the surface there more distant from the Earth s center and thus weakening the gravitational pull. ...