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a b

c d
Fig. 2-27.

Realize that the point chosen as the instantaneous center of zero
velocity for the body can only be used at the instant considered since
the body changes its position from one instant to the next. The locus
of points which define the location of the IC during the body’s motion
is called a centrode, Fig. 2-27,a, and so each point on the centrode
acts as the IC for the body only for an instant.
For exemple, as the board slides downward to the left it is
subjected to general plane motion, Fig. 2-28. Since the directions of
the velocities of its ends A and B are known, the IC is located as
shown. At this instant the board will momentarily rotate about this
point. Draw the board in several other positions and establish the IC
for each case.

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