  The approach to a substantiation of thermodynamics is offered. A conservative
system of interacting elements, which is not in equilibrium, is used as a
model. This system is then split into small subsystems that are accepted as
being in equilibrium. Based on the D'Alambert equation for a subsystem the
generalized Liouville equation is obtained. A necessary condition for
irreversibility is determined. This condition is dependence the forces of
interaction of subsystems on relative velocities. The equation of motion of
subsystems of potentially interacting elements is obtained. The
non-potentiality of the forces of interaction of the subsystems consisting of
potentially interacting elements is proved. The mechanism of occurrence of
irreversible dynamics is offered. The formula that expresses the entropy
through the forces of interaction of subsystems is obtained. The theoretical
link between classical mechanics and thermodynamics is analyzed.
