Applying the universal forcemomentum law to each and every fluid
element, and integrating acorss these elements and over time.
This
quantifies the behavior of a fluid under any known set of forces.
The respective equation is known as 'the equation of motion' or as
'Cauchy's Equation'.
To work one has to know the current velocities of all fluid elements,
and the exact forces thereto.
The equation of motion is solved in two ways:
