# Dynamic Pressure - Compressible flow

## Description

In incompressible fluid dynamics dynamic pressure (indicated with q, or Q, and sometimes called velocity pressure) is the quantity defined as shown.

Dynamic pressure is the kinetic energy per unit volume of a fluid particle. Dynamic pressure is in fact one of the terms of Bernoulli’s equation, which can be derived from the conservation of energy for a fluid in motion. In simplified cases, the dynamic pressure is equal to the difference between the stagnation pressure and the static pressure.

Many authors define dynamic pressure only for incompressible flows. (For compressible flows, these authors use the concept of impact pressure.) However, some British authors extend their definition of dynamic pressure to include compressible flows.

If the fluid in question can be considered an ideal gas (which is generally the case for air), the dynamic pressure can be expressed as a function of fluid pressure and Mach number.

Related formulas## Variables

q | dynamic pressure (pascal) |

γ | ratio of specific heats (non-dimensional) (1.4 for air at sea level conditions) (dimensionless) |

p_{s} | static pressure (pascal) |

M | Mach number (dimensionless) |