Introduction

The equations that govern the changes of the flow quantities over a normal shock are called the Rankine-Hugoniot relations and are the topic of this document. I have always had some problems with the derivations of these equations that I find in text books:

• They are very messy. Lots of random formulaes are applied in random order that I cannot remember. So I have to relearn the long derivations each time I teach it.
• Relatively simple results seem to come out as a miracle. There is no logic why the formulae come out as they do.
• It is hard to separate the important from the less important among the pages and pages of big formulae.
• It seems only to apply to calorically perfect gases. It is not clear what would carry over to say a Van der Waals gas and what not.

This document is my attempt to derive things in a logical way that is instructive.