Important Equations and Quantities
Non Si Units for pressure
PSI: PSI stands for pounds per square inch. One PSI is equal to 6,894.76 Pascals
Atm: Atm stands for Atmosphere. This is the atmospheric pressure at sea level. I atm is equal to 101,325 Pascals
Hydrostatic pressure (head pressure)
ρ (rho) is the density of the fluid (i.e., the practical density of fresh water is 1000 kg/m3); g is the acceleration due to gravity (approximately 9.81 m/s2 on earth's surface); h is the height of the fluid column (in metres). Other units can be used if the rest of the units used in the equation are defined in a consistent way.
It is important to realize that air is a fluid. This equation can be used to find the pressure created by air. This also means that if we are trying to find the pressure of a liquid open to the atmosphere, we must add in the atmospheric pressure to the pressure of the liquid to find the total pressure.
Pressure is force divided by area, so in a sense it does have a direction as force has a direction. The term pseudovector is sometimes used for such quantities.