Moving IC point


The "Instantaneous Center of Zero Velocity" or IC, is the point on a moving body that has zero velocity. The IC does not have to be on the actual body.
The IC may move as the body moves. If the IC is used as the reference point, the relative velocity equation becomes
v_{B} = v_{A} + v_{B/A}
v_{B} = 0 + v_{B/A}
v_{B} = ω r_{B/A} 
Perpendicular Lines from Two Know Velocity Vectors Locate the IC point
Special Cases With
Parallel Velocity Vectors


This is the same relationship that was developed for fixed rotation of a rigid body. The only difference is IC may not be a fixed point, and needs to be found.
In general, the velocity direction and magnitude of one point and the velocity direction of another point on the same body need to be known to use the IC method.
In most cases, lines perpendicular to the two velocity vectors will intersect at the IC point as shown.
If the velocity vectors are parallel, then the distance from the IC to the velocity vectors is proportional, as shown in the figures.
If the velocity vectors are parallel and have the same magnitude and direction, then there is no IC and the body has no rotation.
