Blundell Thermal Physics · Problem 32.3
Shock waves
Physics — Statistical Mechanics · rankine-hugoniot-monatomic-strong-shock
Problem
For a shock wave in a monatomic gas show that in the limit .Intuitive explanation
Shock waves involve a discontinuous jump in fluid properties, but the key is that conservation laws—mass, momentum, and energy—still hold across the discontinuity. In the strong-shock limit (), the upstream flow is supersonic and carries enormous kinetic energy that gets converted into pressure, density, and heat on the downstream side. By applying the Rankine-Hugoniot relations and using the equation of state for a monatomic gas, you can show how each ratio scales with and find the asymptotic limits where the density ratio saturates at 4 (a geometric limit from the equations) while pressure and temperature grow quadratically with Mach number.
Intuitive explanation
Shock waves involve a discontinuous jump in fluid properties, but the key is that conservation laws—mass, momentum, and energy—still hold across the discontinuity. In the strong-shock limit (), the upstream flow is supersonic and carries enormous kinetic energy that gets converted into pressure, density, and heat on the downstream side. By applying the Rankine-Hugoniot relations and using the equation of state for a monatomic gas, you can show how each ratio scales with and find the asymptotic limits where the density ratio saturates at 4 (a geometric limit from the equations) while pressure and temperature grow quadratically with Mach number.