  We derive the effective Lagrangian of the physical four-dimensional fields in
the Randall-Sundrum (RS) model, and use this to calculate the Newtonian
gravitational potential between two point sources on the brane. The effect of
the radion is emphasized, and it is shown to disappear when the hidden brane is
taken to infinity, i.e. when we only have one brane. As a preliminary, we
derive the corresponding Lagrangian in the simpler geometry of a flat spacetime
with one extra dimension compactified on a torus. We also study the gauge
invariance of the theory, and note that the massless vector field that is
present for the torus disappears in the RS model because of the orbifold
symmetry.
