  The time-dependent Casimir-Polder force arising during the time evolution of
an initially bare two-level atom, interacting with the radiation field and
placed near a perfectly conducting wall, is considered. Initially the
electromagnetic field is supposed to be in the vacuum state and the atom in its
ground state. The analytical expression of the force as a function of time and
atom-wall distance, is evaluated from the the time-dependent atom-field
interaction energy. Physical features and limits of validity of the results are
discussed in detail.
