  The evolution of spatially homogeneous and isotropic cosmological models
containing a perfect fluid with equation of state p=w\rho\ and a cosmological
constant \Lambda\ is investigated for arbitrary combinations of w and \Lambda,
using standard qualitative analysis borrowed from classical mechanics. This
approach allows one to consider a large variety of situations, appreciating
similarities and differences between models, without solving the Friedmann
equation, and is suitable for an elementary course in cosmology.
