Watch
Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made.
Favorite
Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students.
Gauge Pressure and Atmospheric Pressure
Pressure is often measured as gauge pressure, which is defined as the absolute pressure minus the atmospheric pressure.
Learning Objectives

Provide relationship between the absolute pressure, the gauge pressure, and the atmospheric pressure

Determine when the the atmospheric pressure and gauge pressure should be used
Key Points

Atmospheric pressure is a measure of absolute pressure and is due to the weight of the air molecules above a certain height relative to sea level, increasing with decreasing altitude and decreasing with increasing altitude.

Gauge pressure is the additional pressure in a system relative to atmospheric pressure. It is a convenient pressure measurement for most practical applications.

While gauge pressure is more convenient for practical measurements, absolute pressure is necessary for most pressure calculations, thus the atmospheric pressure must be added to the gauge pressure for calculations.
Term

Gauge Pressure
The pressure of a system above atmospheric pressure.
Full Text
Atmospheric Pressure
An important distinction must be made as to the type of pressure quantity being used when dealing with pressure measurements and calculations. Atmospheric pressure is the magnitude of pressure in a system due to the atmosphere, such as the pressure exerted by air molecules (a static fluid) on the surface of the earth at a given elevation. In most measurements and calculations, the atmospheric pressure is considered to be constant at 1 atm or 101,325 Pa, which is the atmospheric pressure under standard conditions at sea level.
Atmospheric pressure is due to the force of the molecules in the atmosphere and is a case of hydrostatic pressure. Depending on the altitude relative to sea level, the actual atmospheric pressure will be less at higher altitudes and more at lower altitudes as the weight of air molecules in the immediate atmosphere changes, thus changing the effective atmospheric pressure. Atmospheric pressure is a measure of absolute pressure and can be affected by the temperature and air composition of the atmosphere but can generally be accurately approximated to be around standard atmospheric pressure of 101,325 Pa. Within the majority of earth's atmosphere, pressure varies with height according to . In this equation p_{0} is the pressure at sea level (101,325 Pa), g is the acceleration due to gravity, M is the mass of a single molecule of air, R is the universal gas constant, T_{0} is the standard temperature at sea level, and h is the height relative to sea level.
Gauge Pressure
For most applications, particularly those involving pressure measurements, it is more practical to use gauge pressure than absolute pressure as a unit of measurement. Gauge pressure is a relative pressure measurement which measures pressure relative to atmospheric pressure and is defined as the absolute pressure minus the atmospheric pressure. Most pressure measuring equipment give the pressure of a system in terms of gauge pressure as opposed to absolute pressure. For example, tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, and altimeter pressures must be absolute.
For most working fluids where a fluid exists in a closed system, gauge pressure measurement prevails. Pressure instruments connected to the system will indicate pressures relative to the current atmospheric pressure. The situation changes when extreme vacuum pressures are measured; absolute pressures are typically used instead.
To find the absolute pressure of a system, the atmospheric pressure must then be added to the gauge pressure. While gauge pressure is very useful in practical pressure measurements, most calculations involving pressure, such as the ideal gas law, require pressure values in terms of absolute pressures and thus require gauge pressures to be converted to absolute pressures.
Assign just this concept or entire chapters to your class for free.
Key Term Reference
 Law
 Appears in this related concepts: TwoComponent Forces, Damped Harmonic Motion, and Models, Theories, and Laws
 Pressure
 Appears in this related concepts: SI Units of Pressure, Physics and Engineering: Fluid Pressure and Force, and Surface Tension and Capillary Action
 acceleration
 Appears in this related concepts: Centripetial Acceleration, Position, Displacement, Velocity, and Acceleration as Vectors, and Applications and ProblemSolving
 application
 Appears in this related concepts: Physics and Other Fields, The First Law, and XRay Imaging and CT Scans
 closed system
 Appears in this related concepts: Rotational Collisions, Momentum, Force, and Newton's Second Law, and Measurements: Gauge Pressure and the Barometer
 current
 Appears in this related concepts: Reporting LongTerm Liabilities, Magnetic Force Between Two Parallel Conductors, and The Junction Rule
 equation
 Appears in this related concepts: A General Approach, Equations and Inequalities, and Equations and Their Solutions
 fluid
 Appears in this related concepts: Pumps and the Heart, Diffusion, and Drag
 force
 Appears in this related concepts: Work Done by a Variable Force, Driven Oscillations and Resonance, and Glancing Collisions
 gas constant
 Appears in this related concepts: Equations of State, Isothermal Processes, and Avogador's Number
 gravity
 Appears in this related concepts: Properties of Electric Charges, Defining Graviational Potential Energy, and Key Points: Range, Symmetry, Maximum Height
 ideal gas
 Appears in this related concepts: Overview of Temperature and Kinetic Theory, Kinetic Molecular Theory and Gas Laws, and Boyle's Law: Volume and Pressure
 magnitude
 Appears in this related concepts: Roundoff Error, Multiplying Vectors by a Scalar, and Components of a Vector
 mass
 Appears in this related concepts: Mass Spectrometer, Mass, and Pop Art
 relative
 Appears in this related concepts: Relative Deprivation Approach, Relative Velocity, and Addition of Velocities
 static
 Appears in this related concepts: Translational Equilibrium, Time and Motion, and Alternative Views
 weight
 Appears in this related concepts: Friction: Static, Weight of the Earth, and Einstein Coefficients
Sources
Boundless vets and curates highquality, openly licensed content from around the Internet. This particular resource used the following sources:
Cite This Source
Source: Boundless. “Gauge Pressure and Atmospheric Pressure.” Boundless Physics. Boundless, 02 Jul. 2014. Retrieved 23 Apr. 2015 from https://www.boundless.com/physics/textbooks/boundlessphysicstextbook/fluids10/densityandpressure92/gaugepressureandatmosphericpressure3411642/