  We consider the force on the end of a polymer chain being pulled through a
network at velocity $v$, using computer simulations. We develop algorithms for
measuring the force on the end of the chain using lattice models of polymers.
Our algorithm attaches a spring to the end being pulled and uses its average
extension to calculate the force. General problems associated with the use of
lattice models in obtaining forces are discussed. Variants of this method are
used to obtain upper and lower bounds to the force. The results obtained are in
agreement with recent analytical predictions and experiments.
