  Ehrenfest's theorem in the infinite square well is up to now only manifested
indirectly. The manifestation of this theorem is first done in the finite
square well, and then consider the infinite square well as the limit of the
finite well. For a direct manifestation, we need a more precise formula to
describe the degree of infiniteness of the divergent potential energy. We show
that the potential energy term term, which is the product of the potential
energy and the energy eigenfunction, is a well defined function which can be
expressed in terms of Dirac delta functions. This means that the infinity in
this model is not that vague but has obtained a specification. This results
that expectation values can be calculated precisely and Ehrenfest's thereom can
be confirmed directly.
