Introduction

The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. Two other methods are isentropic and Prandtl-Meyer compressions. The method of compression of a gas results in different temperatures and densities for a given pressure ratio, which can be analytically calculated for a non-reacting gas. A shock wave compression results in a loss of total pressure, meaning that it is a less efficient method of compressing gases for some purposes, for instance in the intake of a scramjet. The appearance of pressure-drag on supersonic aircraft is mostly due to the effect of shock compression on the flow. It has been suggested that this article or section be merged with Sound barrier. ... An isentropic process (a combination of the Greek word iso -same- and entropy) is one during which the entropy of working fluid remains constant. ... Ludwig Prandtl Ludwig Prandtl (4 February 1875 - 15 August 1953) was a German physicist. ... A scramjet (supersonic combustion ramjet) is a variation of a ramjet where the flow of the air and combustion of the fuel air mixture through the engine happen at supersonic speeds. ...

When an object (or disturbance) moves faster than the information about it can be propagated into the surrounding fluid, fluid near the disturbance cannot react or "get out of the way" before the disturbance arrives. In a shock wave the properties of the fluid (density, pressure, temperature, velocity, Mach number) change almost instantaneously. Measurements of the thickness of shock waves have resulted in values approximately one order of magnitude greater than the mean free path of the gas investigated. Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ... Temperature is also the name of a song by Sean Paul. ... The velocity of an object is simply its speed in a particular direction. ... Mach number (Ma) (pronounced in British English with a Germanic ch, as mack or mark and as mock in American English) is defined as a ratio of the speed of an object or flow relative to the speed of sound in the medium through which it is travelling: Vo/Vs... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ... For sound waves in an enclosure, the mean free path is the average distance the wave travels between reflections off of the enclosures walls. ...

Shock waves are not sound waves; a shock wave takes the form of a very sharp change in the gas properties on the order of micro-meters in thickness. Shock waves in air are heard as a loud "crack" or "snap" noise. Over time a shock wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air and loses energy. The sound wave is heard as the familiar "thud" or "thump" of a sonic boom, commonly created by the supersonic flight of aircraft. It has been suggested that this article or section be merged with Supersonic. ... It has been suggested that this article or section be merged with Sound barrier. ...