  We have considered gravity in a five-dimensional warped product space-time,
with a time-dependent warp factor and a time-dependent extra dimension. The
five-dimensional field equations are derived for a spatially flat FRW brane and
the energy conditions and the nature of bulk geometry have been examined. It is
found that the expansion of the four-dimensional universe depends on its
location along the extra dimension and will be different at different locations
in the bulk spacetime. At low energies, the trapping of fields within the brane
implies a specific correlation between the warp factor and the
extra-dimensional scale factor. Generally, the bulk is not conformally flat. At
high energies, the bulk is assumed to be sourced by a scalar field with
self-interaction. The analysis shows that the potential of the scalar field
source of gravity at a given position along the fifth dimension, is related to
the Hubble parameter on the brane at that position in the bulk.
