atmospheric pressure

(noun)

the pressure caused by the weight of the atmosphere above an area

Related Terms

Examples of atmospheric pressure in the following topics:

  • Gauge Pressure and Atmospheric Pressure

    • Pressure is often measured as gauge pressure, which is defined as the absolute pressure minus the atmospheric pressure.
    • Atmospheric pressure is due to the force of the molecules in the atmosphere and is a case of hydrostatic 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.
    • 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.
    • Explain the relationship among absolute pressure, gauge pressure, and atmospheric pressure

  • Measurements: Gauge Pressure and the Barometer

    • Gauge pressure is the pressure of a system above atmospheric pressure.
    • Barometers are devices used to measure pressure and were initially used to measure atmospheric pressure.
    • Early barometers were used to measure atmospheric pressure through the use of hydrostatic fluids.
    • As the atmospheric pressure changes, the pressure exerted by the atmosphere on the fluid reservoir exposed to the atmosphere at the base changes, increasing as the atmospheric pressure increases and decreasing as the atmospheric pressure decreases.
    • The height of the liquid within the glass column then gives a measure of the atmospheric pressure.

  • Gas Pressure and Respiration

    • Gas pressures in the atmosphere and body determine gas exchange: both O2 and CO2 will flow from areas of high to low pressure.
    • Approximately 21 percent of atmospheric gas is oxygen.
    • Patm, the atmospheric pressure, is the sum of all of the partial pressures of the atmospheric gases added together: Patm = PN2 + PO2 + PH2O + PCO2= 760 mm Hg.
    • The pressure of the atmosphere at sea level is 760 mm Hg.
    • For this calculation, the water pressure (47 mm Hg) is subtracted from the atmospheric pressure: 760 mm Hg 47 mm Hg = 713 mm Hg, and the partial pressure of oxygen is: (760 mm Hg 47 mm Hg) 0.21 = 150 mm Hg.

  • Dalton's Law of Partial Pressure

    • The air in the atmosphere is an mixture of many different gases, that vary in concentration.
    • Dalton's law also implies that the relative concentration of gasses (their partial pressures) does not change as the pressure and volume of the gas mixture changes, so that air inhaled into the lungs will have the same relative concentration of gasses as atmospheric air.
    • Because gasses flow from areas of high pressure to areas of low pressure, atmospheric air has higher partial pressure of oxygen than alveolar air (PO2=159mmHg compared to PAO2=100 mmHg).
    • Similarly, atmospheric air has a much lower partial pressure for carbon dioxide compared to alveolar air (PCO2=.3mmHg compared to PACO2=40 mmHg).
    • While inhaled air is similar to atmospheric air due to Dalton's law, exhaled air will have relative concentrations that are in between atmospheric and alveolar air due to the passive diffusion of gasses during gas exchange.

  • The Mechanics of Human Breathing

    • Both inhalation and exhalation depend on pressure gradients between the lungs and atmosphere, as well as the muscles in the thoracic cavity.
    • As volume decreases, pressure increases and vice versa .
    • This decrease of pressure in the thoracic cavity relative to the environment makes the cavity pressure less than the atmospheric pressure .
    • This pressure gradient between the atmosphere and the thoracic cavity allows air to rush into the lungs; inhalation occurs.
    • Air rushes out of the lungs due to the pressure gradient between the thoracic cavity and the atmosphere.

  • Constant Pressure and Volume

    • An isobaric process occurs at constant pressure.
    • Since the pressure is constant, the force exerted is constant and the work done is given as PΔV.
    • An example would be to have a movable piston in a cylinder, so that the pressure inside the cylinder is always at atmospheric pressure, although it is isolated from the atmosphere.
    • If a gas is to expand at a constant pressure, heat should be transferred into the system at a certain rate.
    • Since pressure is constant, the work done is PΔV.

  • The Evaporating Atmosphere

    • Left to equilibration, many compositions will form a uniform single phase, but depending on the temperature and pressure even a single substance may separate into two or more distinct phases.
    • At room temperature and pressure, the water jar reaches equilibrium when the air over the water has a humidity of about 3%.
    • At 100 °C and atmospheric pressure, equilibrium is not reached until the air is 100% water.
    • The Earth's atmosphere is not unchanging.
    • Collisions between water molecules in the atmosphere allows some to condense and some to remain in vapor.

  • Variation of Pressure With Depth

    • Pressure is defined in simplest terms as force per unit area.
    • However, when dealing with pressures exerted by gases and liquids, it is most convenient to approach pressure as a measure of energy per unit volume by means of the definition of work (W = F·d).
    • For liquids and gases at rest, the pressure of the liquid or gas at any point within the medium is called the hydrostatic pressure.
    • As a result, pressure within a liquid is therefore a function of depth only, with the pressure increasing at a linear rate with respect to increasing depth.
    • Equation 2 by itself gives the pressure exerted by a liquid relative to atmospheric pressure, yet if the absolute pressure is desired, the atmospheric pressure must then be added to the pressure exerted by the liquid alone.

  • Basic Principles of Gas Exchange

    • For example, the atmosphere consists of oxygen, nitrogen, carbon dioxide, and other gaseous molecules, and this gaseous mixture exerts a certain pressure referred to as atmospheric pressure (Table 2).
    • For example, in the atmosphere, oxygen exerts a partial pressure, and nitrogen exerts another partial pressure, independent of the partial pressure of oxygen (Figure 1).
    • The composition of air in the atmosphere and in the alveoli differs.
    • The amount of water vapor present in alveolar air is greater than that in atmospheric air (Table 3).
    • In addition, alveolar air contains a greater amount of carbon dioxide and less oxygen than atmospheric air.

  • Earth's Atmosphere

    • The Earth's atmosphere is a layer of mixed gases that is trapped near the surface due to gravitational forces.
    • In the 1800s, scientists, including John Dalton, realized that the atmosphere was composed of a variety of gases.
    • Both air pressure and density increase upon approaching the Earth's surface.
    • In the recent past, we have damaged our ozone layer by putting chlorofluorocarbons (CFCs) into the atmosphere.
    • Recall the composition and relative amounts of the various gases that make up the Earth's atmosphere and how the atmosphere helps the planet survive