The instantaneous center of velocity (IC) is a unique reference point which momentarily has a velocity of zero magnitude. Thus, as far as velocities are concerned, the body seems to rotate about the instantaneous center, that is, the velocity of any point on the rigid body is simply the angular velocity of the rigid body times the distance to the IC.

Plane motion of all particles in a slab can always be replaced by the translation of an arbitrary
point A and a rotation about A with an angular velocity that is independent of the choice of A.

The same translational and rotational velocities at A are obtained by allowing the slab to rotate
with the same angular velocity about the point C on a perpendicular to the velocity at A.

The velocities of all other particles in the slab are the same as originally defined since the angular
velocity and translational velocity at A are equivalent.

As far as the velocities are concerned, the slab seems to rotate about the instantaneous center of
rotation C.

If the velocity at two points A and B are known, the instantaneous center of rotation lies at the
intersection of the perpendiculars to the velocity vectors through A and B .

If the velocity vectors are parallel, the instantaneous center of rotation is at infinity and the
angular velocity is zero.

If the velocity vectors at A and B are perpendicular to the line AB, the instantaneous center of
rotation lies at the intersection of the line AB with the line joining the extremities of the velocity
vectors at A and B.

If the velocity magnitudes are equal, the instantaneous center of rotation is at infinity and the
angular velocity is zero.