
In motion analysis, investigators generally rely on an inertial reference frame to describe different mechanical quantities. The typical outcome of a generalpurpose motion analysis package includes the position, velocity & acceleration of the joints and the CMs, the angular velocity & acceleration of the segments, and the joint angles & their timederivatives basically expressed in terms of the inertial reference frame. One can always express the equations of motion for a system in an inertial reference frame. But there are several occasions where it is more advantageous to use some noninertial reference frames. Noninertial frames allow the investigators to simplify the equations of motion significantly. Using noninertial frames and subsequently describing different motion quantities in the noninertial frames can enrich the analysis to a great extent. The human body consists of several [rigid] segments interlinked to each other. Motion of a body segment is characterized by the translation of the segment's CM and the rotation about its CM. One can describe the motion of a distal segment in relation to that of a proximal segment. In this process, one easily encounters a rotating reference frame. This section explains how to deal with a rotating reference frame to express the motions of equation effectively. The main issues here are:

© YoungHoo Kwon, 1998 