### pressure:

Abdominal pressure
* is raised due to abdominal muscle contraction and to the descent of diaphragm.
* last resort with infants because of their liver development.

Absolute pressure
* can vary with weather conditions.
* is based on a zero reference point, the perfect vacuum
  - referenced against absolute zero pressure, or a complete vacuum
  - the total pressure as measured againgst a vacuum
  - used when calculating flow and fluid properties

### pressure:

Air pressure
* Most air pressure causes air movement
* Most air pressure causes rapid air movement
  - wind
* Some air pressure affects evaporation
* Some air pressure is caused by displacement
  - elevation
  - weather
* acting up against an object in air is greater than the pressure above pushing down.
* can be a hard scientific concept to grasp
  - determine different weather conditions
  - to move rapidly into that vaccuum
* changes with the weather.
* decreases as altitude increases.
* decreases with altitude, therefore, air expands as it rises in the atmosphere
  - an increase in elevation
  - height, and as the thermal rises, there is less pressure on it
* exerts a force from high toward lower pressure.
* flowing on top of a curved airplane's wing causes the airplane to rise.
* force that acts on the outside surface.
* forces the eggs out of the body cavity into a pan.
* increases when the concentration of water vapor in the air increases
  - with temperature
* indicates weather.
* is analogous to water pressure
  - applied to the surface of hydraulic fluid in a reservoir
  - caused by the weight of air above the point where the pressure is being experienced
  - converted into hydraulic pressure
* is created by the molecules moving around
  - motion, size, and number of gas molecules present in the air
  - weight of the earth's atmosphere
  - gas pressure
  - greater at low elevations and less at high altitudes
  - greatest at the earth's surface and decreases with altitude
  - introduced into the ear canal, and the movement of the eardrum is measured
  - lower, so water has a lower boiling point and liquids evaporate faster
  - measured at the height of the electronics enclosure
* is measured by a barometer
  - observing the height of the column of mercury in the tube
  - in hectopascals
* is measured with a barometer
  - an instrument called a barometer
  - simply the weight of air pressing down onto the surface of the earth
  - supplied by a can of compressed air
  - the driving force for atmospheric motions
* is the force exerted by the weight of air above
  - of air against a unit of area
* is the weight of a column of air pushing down on an area
  - the air pressing against the surface of the earth
* is used to blow the ballast to surface the submarine
  - push a rocket through the ground from one hole to the other
* is usually higher on the eastern side of the Pacific Ocean near South America
  - lower over the western side of the Pacific Ocean near Australia
* measure of how much atmospheric mass is present above a given location
  - the weight of the air
* plays a major role in determining weather patterns.
* pushes down on the surface of the mercury, making some rise up the tube.
* refers to the force that is exerted by the Earth's atmosphere on a unit surface area.
* varies with elevation but also with weather systems
  - time

Alveolar pressure
* equals atmospheric pressure at end expiration of a normal breath.
* is given with respect to atmospheric pressure, which is always set tozero
  - greater than atmospheric pressure during an expiration
  - less than atmospheric pressure during a normal inspiration
  - the sum of pleural pressure and elastic recoil of the lung