Generating a circle by a rotating vector
(2) When it is necessary to determine the number of complete rotations that
shaft or wheel makes, it is customary to say 300 revolutions, 60 revolutions, etc.
This is the revolution method of describing rotary motion.
Still another way of
describing angular displacement is by radian measure.
When the length of the
radius of the circle is laid off on the circumference, an angle called a radian is
determined. Figure 2 shows the radian designated by .