Word of the Day -- Shock Wave

A shock wave is a type of propagating disturbance. When a wave moves faster than the speed of sound in a liquid, gas or plasma (a "fluid", in physics terminology) it is a shock wave. Like an

ordinary wave, a shock wave carries energy, and can propagate through a medium. It is characterized

by an abrupt, nearly discontinuous change in pressure, temperature and density of the medium. In

supersonic flows, expansion is achieved through an expansion fan.

Unlike solitons (another kind of nonlinear wave), the energy of a shock wave dissipates relatively quickly with distance. Also, the accompanying expansion wave approaches and eventually merges with the shock wave, partially cancelling it out. Thus the sonic boom associated with the passage of a supersonic aircraft is the sound wave resulting from the degradation and merging of the shock wave and the expansion wave produced by the aircraft.

When a shock wave passes through matter, the total energy is preserved but the energy which can be extracted as work decreases and the entropy increases. This, for example, creates additional drag force on aircraft with shocks.

Shock waves can travel through any medium, including solids, liquids, gasses, and plasmas.