When there is a groove, the inside face restrains the stylus, so there is effectively no such force, because the arm is rotating only minimally (at less than 0.01 rpm), and the stylus has such a tiny mass, that any forces are negligible, and totally overwhelmed by the friction forces by many orders of magnitude.
J
John_gordon (Answers | This Thread)
As a layman, this would most closely resembles my experiences. Well put J.