  The Dirac particle S_D is investigated by means of dynamic methods, i.e.
without a use of the principles of quantum mechanics. It is shown that the
Pauli particle S_P and the nonrelativistic approximation S_{nD} of the Dirac
particle S_D are different dynamic systems. S_{nD} contains the high frequency
degrees of freedom, which are absent in the dynamic system S_P. It means that
the nonrelativistic Dirac particle S_{nD} is composite (i.e. it has internal
degrees of freedom), whereas the Pauli particle S_P is a pointlike particle
with the spin. In the absence of the electromagnetic field the world line of
the classical Pauli particle S_{Pcl} is a timelike straight, whereas that of
the classical nonrelativistic Dirac particle S_{nDcl} is a helix. The
characteristic frequency $\Omega =2mc^{2}/\hbar $ of this helix is the
threshold frequency of the pair production. Using dynamic methods, one shows
freely that the Copenhagen interpretation, when the wave function is a specific
quantum object describing the state of individual particle, is incompatible
with the quantum mechanics formalism. Besides, it is shown that the momentum
distribution in quantum mechanics is in reality the mean momentum distribution.
Effectiveness of different investigation strategies is discussed and compared.
