I am wondering, when solving rigid body exercises, how can I express the relationship between linear and angular acceleration for a general case? E.g. what would be the linear acceleration in function of the angular one of a $1\, \mathrm m$ rod that is rotating through a fixed point $0.6\, \mathrm m$ away from its mass center? And what about the case of a yoyo?
Edit: I know the basic relation $a= \alpha R$, but I am confused as to how to choose $R$ and my textbook is not helping.