  Analytical expressions for the elastic and dynamic form factors (FFs) are
derived in the shell model (SM) with a potential well of finite depth. The
consideration takes into account the motion of the target-nucleus center of
mass (CM). Explanation is suggested for a simultaneous shrinking of the density
and momentum distributions of nucleons in nuclei. The convenient working
formulae are given to handle the expectation values of relevant multiplicative
operators in case of the 1s-1p shell nuclei.
