  Combined action of weak and strong pinning centers on the vortex lattice
complicates magnetic behavior of a superconductor since temperature and
magnetic field differently affect weak and strong pinning. In this paper we
show that contributions of weak and strong pinning into magnetization of the
layered superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ can be separated and
analyzed individually. We performed a careful analysis of temperature behavior
of the relaxed superconducting current $J$ in YBa$_2$Cu$_3$O$_{7-\delta}$ films
which revealed two components of the current $J = J_1 +J_2$. A simple method of
separation of the components and their temperature dependence in low magnetic
fields are discussed. We found that $J_1$ is produced by weak collective
pinning on the oxygen vacancies in CuO$_2$ planes while $J_2$ is caused by
strong pinning on the Y$_2$O$_3$ precipitates. $J_1$ component weakly changes
with field and quasi-exponentially decays with temperature, disappearing at $T
\simeq 30$--40~K. Rapid relaxation of $J_1$ causes formation of the normalized
relaxation rate peak at $T \simeq 20$~K. $J_2$ component is suppressed by field
as $J_2\propto B^{-0.54}$ and decays with temperature following to the power
law $J_2\propto(1 - T/T_\mathrm{dp} )^\alpha$ where $T_\mathrm{dp}$ is the
depinning temperature. Detailed comparison of the experimental data with
pinning theories is presented.
