  I discuss an apparently simple ballistics problem: the time it takes an
object to fall a small vertical distance near the surface of the Earth. It
turns out to be not so simple; I spend a great deal of time on the quantitative
assessment of the assumptions involved, especially with regards to the
influence of the air. The point is \emph{not} to solve the problem; indeed I
don't even end up solving the problem exactly. I introduce dimensional analysis
to perform all of the calculations approximately. The principal theme of the
lecture is that \emph{real} physics can be very different from ``textbook''
physics, since in the real world you aren't ever told what equations are
appropriate, or why.
