  We show that the motion of the neutral masses in an accretion disk orbiting a
black hole creates a general-relativistic magnetic-like (gravitomagnetic) field
that vertically accelerates neutral particles near the accretion disk upward
and then inward toward the axis of the accretion disk. Even though this
gravitomagnetic field alone does not achieve collimated jets, it is a novel
means to identify one general relativistic effect from a much more complicated
problem. In addition, as the accelerated material above or below the accretion
disk nears the axis with a nearly vertical direction, a frame-dragging effect
twists the trajectories around the axis thus contributing to the formation of
collimated bipolar jets.
