Shock is formed due to coalescence of various small pressure pulses.
[clarification needed] However, if the object itself happens to travel at speed greater than sound, then the disturbances created by the object would not have traveled and communicated to the rest of the flow field and this results in an abrupt change of property, which is termed as shock in gas dynamics terminology.
Shocks are characterized by discontinuous changes in flow properties such as velocity, pressure, temperature, etc.
Shocks are irreversible occurrences in supersonic flows (i.e. the entropy increases).
T is temperature, M is the mach number, P is pressure, ρ is density, and γ is the ratio of specific heats.