We postulate the basic principle of dynamics and derive the second equation
of the fluid model, the equation of motion. The dynamics of the fluid is investigated.
We introduce the notion of momentum of the body, study the rate of change of
momentum and discuss forces acting on a body. The body forces and the contact forces
and corresponding densities are considered. The equation of motion in the Cauchy form
is obtained. Finally, we propose the simplest form of the stress tensor which gives the
equation of motion of the perfect fluid.
Keywords: Basic principle of dynamics, Body force, Center of mass, Contact
force, Equation of motion, Momentum, Momentum balance equation, Normal
stress, Orientation, Perfect fluid, Potential, Shear stress, Stress tensor.
