  The elements of the cold magnetic driven flows behave like beads on the
magnetic field line. The inclination of the field lines at the surface of the
disc plays a crucial role on the nature of the magnetically driven outflow. For
the non-relativistic case, a centrifugally driven outflow of matter from the
disc is possible, if the poloidal component of the magnetic field makes an
angle of less than a critical 60 degrees with the disc surface. The collimated
flows ejected from active galactic nuclei may probably start from the region
near the black hole. We investigate the dynamical behavior of the 'beads' on
the magnetic field line start from the disc near a black hole. It is found that
the critical angle becomes larger than 60 degrees for the rotating black hole
case (close to 90 degrees for a=1), which may imply that the flows are easy
accelerated in the inner edge of the disk surrounding a rotating black hole.
