Theory of Machine
A combination of kinematic pairs, joined in such a way that the relative motion between the links is completely constrained, is called a
A rigid link rotates instantaneously relative to another link at the instantaneous centre for the configuration of the mechanism considered.
The velocity of the instantaneous centre relative to any third rigid link is same whether the instantaneous centre is regarded as a point on the first rigid link or on the second rigid link.
The two rigid links have no linear velocity relative to each other at the instantaneous centre.
EXAMIANS