Momentum exchange between an electromagnetic wave and a dispersive medium

We present an elementary discussion of the momentum transferred by an electromagnetic wave propagating in a dispersive medium. Our analysis is based on Minkowski's electromagnetic momentum density which have been recently seen to be consistent with a fully covariant expression of the energy-momentum tensor of the electromagnetic field in a dispersive medium and with all the experimental evidence. We show that the medium may be either pulled or pushed as the electromagnetic pulse enters in it depending on the value of the frequency.