THEORY OF SHOCK WAVES AND INTRODUCTION TO GAS DYNAMICS
By
Ya. B. Zeldovich
Introduction
Gas dynamics is a component part of hydrodynamics, the science of fluids, liquids and gases.
A particular feature of gas dynamics is the need to keep account of the compressibility of the medium. Liquids may be considered incompressible under normal circumstances, whereas gases change their volume considerably even under a slight variation in pressure.
It is obvious that specific formulas and laws of gas dynamics have to be applied to gases only insofar as we are dealing with pressure changes of great magnitude.
In the case of small velocities, the motion of gas can be regarded in the same way as the motion of a liquid, i. e., ignoring the change of volume and compressibility.
Depending upon the condition, the order of magnitude of pressure differentials arising in a flow changes from the value of dynamic Impact according to Bernoulli's
