A shock wave is essentially a surface of discontinuity propagating supersonically through a medium. Density, pressure, and temperature are unequal on the different sides of the wave front, clearly distinguishing between the shocked and unshocked material. This is in sharp contrast to subsonic sound waves, where all thermodynamic quantities vary continuously through the medium. In general, the shock compresses and heats the material that it flows through in an irreversible process, again in contrast to sound waves. The fact that the front propagates supersonically with respect to the unshocked material allows for the discontinuity to be maintained as the wave advances, since it impedes information from being transmitted from the region through which the shock has already passed.

Shock waves generally accompany supersonic motion, such as a sonic boom or the impact of projectile on a surface (like a meteor hitting the earth). Shock waves are...