  A wave function can be written in the form of {\psi} = ReiS/h. We put this
form of wave function into quantum mechanics equations and take hydrodynamic
limit, i. e., let Planck constant be zero. Then equations of motion (EOM)
describing the movement of macroscopic bodies are retrieved. From Schrodinger
equation, we obtain Newtonian mechanics, including Newtons three laws of
motion; from decouple Klein-Gordon equation with positive kinetic energy (PKE),
we obtain EOM of special relativity in classical mechanics. These are for PKE
systems. From negative kinetic energy (NKE) Schrodinger equation and decoupled
Klein-Gordon equation, the EOM describing low momentum and relativistic motions
of macroscopic dark bodies are derived. These are NKE systems, i. e., dark
systems. In all cases scalar and vector potentials are also taken into account.
The formalism obtained is collectively called macromechanics. For an isolated
system containing PKE and NKE bodies, both total momentum and total kinetic
energy are conserved. A dark ideal gas produces a negative pressure, and its
microscopic mechanism is disclosed. Two-body problems, where at least one is of
NKE, are investigated for both macroscopic bodies and microscopic particles. A
NKE proton and a PKE electron can compose a stable PKE atom, and its spectral
lines have blue shifts compared to a hydrogen atom. The author suggests to seek
for these spectral lines in celestial spectra. This provides a way to seek for
dark particles in space. Elastic collisions between a body and a dark body are
researched.
