Impact Pressure

Impact Pressure (Dynamic pressure) is the difference between the static pressure and the total pressure. 
Dynamic pressure is associated with fluid motion. The simplest illustration of dynamic pressure is obtained by considering the Bernoulli equation, which for cases of steady flow, constant density, and negligible frictional losses may be written as

where v is the fluid velocity and H is a constant known as the Bernoulli constant, or total head, and is given by conditions of the problem (i.e., this equation states that total head is constant for a given set of flow conditions). Each of the additive terms in the equation has units of length. The first term is known as the velocity head, the second is the pressure head, and the third is the elevation head, or simply elevation.