Force per unit area; absolute pressure equals gauge plus atmospheric.
P=F/A in pascals; 1 atm=101.325 kPa=1.013 bar. Absolute pressure=gauge+atmospheric. Vacuum pressure is below atmospheric. Fluid pressure acts equally in all directions at a point. Measured by manometers, Bourdon gauges and transducers.
A tyre gauge reading of 220 kPa corresponds to 321 kPa absolute.
Pressure drives flows and forces in every thermal system, and mixing up gauge and absolute pressure can change results by a large margin.
Force per unit area; absolute pressure equals gauge plus atmospheric.
Pressure drives flows and forces in every thermal system, and mixing up gauge and absolute pressure can change results by a large margin.
The pressure measured relative to the local atmospheric pressure, so it reads zero when open to the air.
Gas laws require absolute pressure, because a gauge reading of zero still means the gas is at atmospheric pressure.
Typical applications include checking the pressure rating of a steam pipe from a gauge reading, calculating the force on a piston from absolute pressure and setting the pressure of a tyre from a gauge reading at sea level.
Study "Temperature scales" first (topic 5 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Use absolute pressure in gas laws. 1 bar=100 kPa. psi in US units.
A tyre gauge reading of 220 kPa corresponds to 321 kPa absolute.
The next topic is "Specific heat", which builds directly on this one.
It is classed as Beginner in Thermodynamics & Fluids (topic 6 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
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