We construct a micromechanical version of an early model for topologically
constrained polymers -- a 2D chain amongst point-like uncrossable obstacles --
which allows us to explicitly elucidate the role of topological forces beyond
confining the chain to a curvilinear tube-like path. Our simulations reveal
that linear relaxation of the contour length \textit{along the tube} is slowed
down by the presence of topological forces that can be considered as additional
effective topological ``friction'' in quiescence. However, this perspective
fails in predicting the strong forces that resist the imposed curvilinear
motion of the chain during nonlinear startup microrheology. These entropic
forces are nonlocal in nature and result from an unexpected coupling between
orientational and longitudinal dynamics.Comment: Comments welcom