Question

Instantaneous center of rotation of any rigid body is an imaginary point inside or outside the body which is at rest at that moment. The whole body can be visualized to be rotating about this point. So the velocity of any point on the body can be seen to be v = ωr. Where w is the angular velocity of the rigid body and r is the distance of the point from the instantaneous center of rotation (ICR).

One can easily construct a simple demonstration apparatus for student use. The mechanism consists of three links of (in general) different lengths connected in a flexible chain, the outside ends being fixed (figure). As the left-hand link is rotated, the other two links are forced to rotate as well, but not, in general, uniformly. Because points A and D are fixed, the velocity of point B is perpendicular to AB and the velocity of point C is perpendicular to CD. Therefore the instantaneous center of rotation of the central link is located at the intersection of the extensions of AB and CD.