What is the formula for pressure?

Pressure (symbol: p) is the force applied per unit area,  in the direction perpendicular to that surface.

P=F/A, where, F is the normal force, A is the area.

Pressure is a scalar, which in IS is measured in pascals.

1 Pa = 1 N/m2

The pressure is transmitted to surrounding areas or sections of the field of fluid, in the normal direction at any point in these areas or sections.

It is a fundamental parameter in thermodynamics and is a joint variable to volume.

Characteristic Cases

Static pressure

Static pressure, usually denoted SP, is the inner pressure of a fluid which is measured with a device that moves with the same speed as the fluid. For example, to the walls of a pipeline is carried the static pressure of fluid flowing through it.

Dynamic Pressure

Dynamic pressure is the additional pressure of a fluid that would hit an area and would be forced to consume completely it's kinetic energy. It is expressed by the relation:

p dynamic= rho*(v^2/2)

where rho is fluid density in kg/m^3, v is velocity in m / s.

Stagnation pressure

Stagnation pressure is the pressure that would exert a fluid in motion if it were forced to stop. If a fluid moves faster, its stagnation pressure increases. Static pressure and stagnation pressure are related to Mach number of fluid. See also Bernoulli's equation, which however is  valid only for incompressible fluids.Pressure of a fluid in motion can be measured with a Pitot tube, connected to a manometer.

 Hydrostatic pressure

Hydrostatic pressure is the pressure due to the weight of a fluid.

p=rho*g*h

where:

ρ (rho) is density of the fluid (eg water density is almost 1000 kg/m3);

g is the acceleration due to gravity (conventional, 9.80665 m/s2 to the sea surface);

h is the height of column of liquid (in meters).

Pressure of explosion or deflagration

Explosion or deflagration pressures are created by igniting explosive gas, aerosol, suspension in closed or open spaces. These pressures propagate as a wave of shock.

Negative pressures

While pressures are generally positive, in some cases negative pressures are meet:

-When discussing the relative pressures. For example, an absolute pressure of 80 kPa may be expressed as a relative pressure of -21 kPa (ie 21 kPa under atmospheric pressure of 101 kPa). The technique is called "a depression of 21 kPa.

- When attractive forces (eg Van der Waals forces) between particles of fluid, exceeds the forces of rejection. This scenario, however, is unstable because the particles are closer and closer until rejection forces would balance the forces of attraction.

- Negative pressures occurring during plant transpiration.

-Casimir effect can create small forces of attraction by interacting with vacuum energy. Sometimes this is called 'vacuum pressure' (not to be confused with depression).

- Depending on the reference system to surface orientation, a positive pressure on one side of a surface can be considered negative on the other side of the area.

- In cosmology( dark energy, expansion of the universe).