Prometheus, as seen from one end, by the Cassini spacecraft, in 2005. The moon rotates synchronously (as do almost all of Saturn's moons), with the long axis always pointing at Saturn. This view shows the end which points away from Saturn, toward the F ring, which is shepherded by Promethus and Pandora.
(NASA,Cassini Imaging Team)

     Prometheus' interaction with the F ring pulls material toward it, but as it moves past the ring (its smaller orbit gives it a higher angular velocity), very little of the material actually reaches it. Most of the ring particles surge toward Prometheus, then fall backward, towards the ring, creating waves and ripples in the ring. In this process, the pull of the moon tends to actually concentrate material in the ring, rather than spreading it out. This paradoxical result is due to the interaction of the ring particles with the small, temporary pull of Prometheus, and the much larger, permanent pull due to Saturn's gravity (see how satellites shepherd rings).