  Using the plasma model for the metal dielectric function we have calculated
the electromagnetic fluctuation induced forces on a free standing metallic film
in vacuum as a function of the film size and the plasma frequency. The force
for unit area is attractive and for a given film thickness it shows an
intensity maximum at a specific plasma value, which cannot be predicted on the
basis of a non retarded description of the electromagnetic interaction. If the
film is deposited on a substrate or interacts with a plate, both the sign and
the value of the force are modified. It is shown that the force can change sign
from attraction to repulsion upon changing the substrate plasma frequency. A
detailed comparison between the force on the film boundaries and the force
between film and substrate indicates that, for 50-100 nm thick films, they are
comparable when film-substrate distance is of the order of the film thickness.
