Angular Displacement. - By angular displacement of a rotating body during any time interval is meant the angle described during that interval by any line parallel to the plane of rotation. Obviously all such lines turn through equal angles in the same interval; it is convenient, for purposes of illustration, to select a line that cuts the axis. Let the irregular outline (Figure 16) represent a rotating body, the plane of rotation being the plane of the paper and the center of rotation being O. Line OP is a line in the body perpendicular to the axis of rotation, and Ө is the angle between OP and any fixed line of reference OX, also perpendicular to the axis of rotation. As customarily, Ө is regarded as positive when measured counterclockwise from OX to OP. If Ө1and Ө2 denote initial and final values of Ө for any time interval, then the angular displacement for that interval is Ө = Ө2 — Ө1 [2, С. 50 - 51].
Read and translate the text and choose the best summary below.