Theory of Machine
The velocity of piston in a reciprocating steam engine is given by (where ω = Angular velocity of crank, r = Radius of crank pin circle, θ = Angle turned by crank from inner dead center, and n = Ratio of length of connecting rod to the radius of crank)
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.
All of these
The two rigid links have no linear velocity relative to each other at the instantaneous centre.