  Using very general and well established ideas of the statistical physics of
macroscopic bodies, that is, of those composed of many degrees of freedom, we
show how classical behavior of the center of mass motion arises from a fully
quantum mechanical description of the dynamics of the whole body. We do not
attempt to provide a rigorous proof of the latter statement, but rather, we
show or, at least, indicate the hypotheses needed to obtain the purported
result. Moreover, we neither attempt to deal with the "most general" physical
situation and, instead, we concentrate on a stylized model of a small solid,
yet macroscopic, that we shall call a "little stone". The main hypothesis is
that a macroscopic body can be decomposed into several smaller pieces, still
macroscopic, that become statistically independent due to the short-range
interaction nature of their constituent atoms. The ensuing main result is that
the quantum distributions of extensive variables of the body become
sharply-peaked. The center of mass variables are of this type and hence their
dynamics is essentially classical. We point out the crucial role played by the
external potential, in which the motion occurs, as the macroscopic agent that
executes the "measurement" process of the center of mass.
