  In order to find a law characterising the decrease of velocity along a jet,
five analytical methods are suggested. The first two simple models examine the
variation of velocity in the presence of Newton's or Stoke's resistance. The
equation that represents the conservation of the momentum along a pyramidal
sector is solved from an analytical point of view (third model). The
application of the conservation of the total momentum flux allows us to deduce
the velocity of the galaxy as a function of time for classical velocities
(fourth model) and relativistic velocities (fifth model). The variation of
velocity along the jet combined with an adequate composition of jet precession
velocity, rotational velocity of the galaxy, and galaxy dispersion velocity in
the cluster allows us to trace the geometrical pattern of the head-tail radio
sources. Application of the developed theory/code to the radio galaxies
NGC1265,NGC4061,NGC326, and Cygnus A gives the central galaxy's approximate
dispersion velocities in the direction perpendicular to the jet. A transition
from head--tails to classical double radio galaxies as a function of the
increasing jet's mechanical power is introduced.
