  We study flop-transitions for M-theory on Calabi-Yau three-folds and their
applications to cosmology in the context of the effective five-dimensional
supergravity theory. In particular, the additional hypermultiplet which becomes
massless at the transition is included in the effective action. We find the
potential for this hypermultiplet which includes quadratic and quartic terms as
well as additional dependence on the Kahler moduli. By constructing explicit
cosmological solutions, it is demonstrated that a flop-transition can indeed by
achieved dynamically, as long as the hypermultiplet is set to zero. Once
excitations of the hypermultiplet are taken into account we find that the
transition is generically not completed but the system is stabilised close to
the transition region. Regions of moduli space close to flop-transitions can,
therefore, be viewed as preferred by the cosmological evolution.
