  The Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model, a microscopic
transport model, is used to study the directed and elliptic collective flows
and the nuclear stopping in Au+Au collisions at incident energies covered by
INDRA and lower-energy FOPI experiments. It is seen clearly that these
observables are sensitive to both, the potential terms (including iso-scalar
and iso-vector parts as well as the momentum dependent term) in the equation of
state (EoS) and the collision term (including the Pauli-blocking and the
medium-modified nucleon-nucleon elastic cross section (NNECS)). The momentum
modifications of both, the mean-field potentials and the density dependent
NNECS, are found to be sensitive to the collectivity of heavy-ion collisions.
At INDRA energies ($\le 150$~MeV/nucleon), the dynamic transport with a soft
EoS with momentum dependence and with the momentum-modified density-dependent
NNECS describes the directed flow exhibited by hydrogen isotopes ($Z=1$)
emitted at mid-rapidity fairly well.
