  We study the physics of wave propagation in a weakly ionised plasma, as it
applies to the formation of multifluid, MHD shock waves. We model the plasma as
separate charged and neutral fluids which are coupled by ion-neutral friction.
At times much less than the ion-neutral drag time, the fluids are decoupled and
so evolve independently. At later times, the evolution is determined by the
large inertial mismatch between the charged and neutral particles. The neutral
flow continues to evolve independently; the charged flow is driven by and
slaved to the neutral flow by friction. We calculate this driven flow
analytically by considering the special but realistic case where the charged
fluid obeys linearized equations of motion. We carry out an extensive analysis
of linear, driven, MHD waves. The physics of driven MHD waves is embodied in
certain Green functions which describe wave propagation on short time scales,
ambipolar diffusion on long time scales, and transitional behavior at
intermediate times. By way of illustration, we give an approximate solution for
the formation of a multifluid shock during the collision of two identical
interstellar clouds. The collision produces forward- and reverse J shocks in
the neutral fluid and a transient in the charged fluid. The latter rapidly
evolves into a pair of magnetic precursors on the J shocks, wherein the ions
undergo force free motion and the magnetic field grows monotonically with time.
The flow appears to be self similar at the time when linear analysis ceases to
be valid.
