Motion in a Rotating Reference Frame
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In motion analysis, investigators generally rely on an inertial reference frame to describe different mechanical quantities. The typical outcome of a general-purpose 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 time-derivatives 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 non-inertial reference frames. Non-inertial frames allow the investigators to simplify the equations of motion significantly. Using non-inertial frames and subsequently describing different motion quantities in the non-inertial frames can enrich the analysis to a great extent.

The human body consists of several [rigid] segments inter-linked 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:

Rotating Reference Frame
Acceleration of a Particle
Acceleration of a Rigid Body


Young-Hoo Kwon, 1998-