Geometric dynamics is a tool for developing a mathematical
representation of real world phenomena, based on the notion of a field
line described in two ways: -as the solution of any Cauchy problem
associated to a first-order autonomous differential system; -as the
solution of a certain Cauchy problem associated to a second-order
conservative prolongation of the initial system. The basic novelty of
our book is the discovery that a field line is a geodesic of a suitable
geometrical structure on a given space (Lorentz-Udri te world-force
law). In other words, we create a wider class of Riemann-Jacobi,
Riemann-Jacobi-Lagrange, or Finsler-Jacobi manifolds, ensuring that all
trajectories of a given vector field are geodesics. This is our
contribution to an old open problem studied by H. Poincare, S. Sasaki
and others. From the kinematic viewpoint of corpuscular intuition, a
field line shows the trajectory followed by a particle at a point of the
definition domain of a vector field, if the particle is sensitive to the
related type of field. Therefore, field lines appear in a natural way in
problems of theoretical mechanics, fluid mechanics, physics,
thermodynamics, biology, chemistry, etc.