  We discuss some of the properties of the `collision' of a quantum mechanical
wave packet with an infinitely high potential barrier, focusing on novel
aspects such as the detailed time-dependence of the momentum-space probability
density and the time variation of the uncertainty principle product $\Delta x_t
\cdot \Delta p_t$. We make explicit use of Gaussian-like wave packets in the
analysis, but also comment on other general forms.
