"In dealing with a fluid, one is in reality dealing with a system which has many particles which interact with one another. The main utility of fluid dynamics is the ability to develop a formalism which deals solely with a few macroscopic quantities like pressure while ignoring the details of the particle interactions. Therefore, the techniques of fluid dynamics have often been found useful in modeling systems with complicated interactions (which are either not known or very difficult to describe) between the constituents. Thus, the first successful model of the nuclear fission of heavy elements was the liquid drop model of the nucleus, which treats the nucleus as a fluid, and hence replaces the many body problem of calculating the interactions of all of the protons and neutrons with the much simpler problem of calculating the pressures and surface tension in this fluid.1 Of course, this treatment gives only a very rough approximation to reality, but it is nonetheless a very useful way of approaching the problem"-- Provided by publisher.