Air Pressure: Barometric Apparatus Design_

Group: Matthew Sama, Alejandro Quiros, Kathy Yuen, Trinadh Pydipally

_Air Pressure

• Air pressure is the weight of the atmosphere pressing down on a surface, earth’s surface.
• It is measured by a barometer in units called millibars or in inches of mercury.
• The average barometric pressure for the United States is 29.92 inches. The record highest was 31.85” in  Northway, Alaska whereas the record lowest was 26.35”  in Key West, Florida.
• If a high pressure system is on its way, often you can expect cooler temperatures and clear skies. If a low pressure system is coming, then look for warmer weather, storms and rain. The temperature and humidity are directly to the air pressure, as cool moist air is denser and heavier falling to the earth and pushing air outwards as it collides with the surface, while warm dry air moves up from the earths surface into the sky where it will eventually cool and moisture will condense to form clouds or precipitation.
• The weight pressing down on a one square-inch sample of air at sea level is 14.7 pounds, which is equivalent to a column of mercury 29.92 inches in height (1,000 millibars).
• Air pressure changes with altitude. When you move to a higher place, say a tall mountain, air pressure decreases because there are fewer air molecules as you move higher in the sky.

_Barometer Apparatus

The Analog BarometerApparatus was designed as an operable section mechanism to record the various air pressures across the typical workstation of the studio. The various heights of the apparatus included 9-1/2″ Floor, 2′-4″ Half of Radiator, 4′-0″ Radiator, 5′-7″ Human Height, and 7′-2″ Mid Height of Window as a means of getting a wide range of air pressures across the space.

_Apparatus Readings

The Analog Barometer Apparatus was documented over a full 24 hour period recording the air pressure changes from 8:00am Wednesday January 27th 2010 to 8:00 Thursday January 28th 2010. The results of which signified the most radical change in data at Barometer No. 6, based on this reading it was decided to mount the electric barometer at this location as means for comparing the validity of the analog testing.

_Barometer Types:

Liquid Barometers

• Only liquid mercury is dense enough to make a practical liquid barometer for atmospheric conditions. Mercury barometers are mostly found in laboratories and weather stations where very exact measurements of air pressure are needed.
• Water barometers can, however, be designed to show pressure changes over short time periods.

_Aneroid Barometers

• In the aneroid barometer, the pressure sensing unit is a small, flexible metal compartment or diaphragm that has been partially evacuated of air and then tightly sealed.
• When the external ambient pressure changes, it creates a pressure differential between the ambient air and the air sealed within the aneroid cell.
• The pressure differential causes the cell to expand or contract in response.
• Aneroid barometers are ideal for the weather enthusiast as they are often very inexpensive, portable and sufficiently accurate for most uses
• Use detection cells whose resistance or capacitance level changes sufficiently with air pressure to react to the small changes found in the atmosphere.
• The detection cell can be connected to electronic circuits or microprocessors in various ways to provide a wide range of possible applications
• The reading outputs on some units can be downloaded to a computer for storage and analysis.

_Electric Barometers

• Use detection cells whose resistance or capacitance level changes sufficiently with air pressure to react to the small changes found in the atmosphere.
• The detection cell can be connected to electronic circuits or microprocessors in various ways to provide a wide range of possible applications
• The reading outputs on some units can be downloaded to a computer for storage and analysis.

_Preliminary Bottle Barometer Tests

Since air pressure is in direct relation to heat difference, as well as moisture, the most extreme and varied data was found to be at the windows/radiators where the cold draft of the exterior air leaking into the building and the hot air pluming off of the radiator create a close region of different pressures. Additional readings where also taken in various other regions of the studio space such as the door passage, which may cause a distribution of air pressures between the studio and the hallway.

It is also of interest to record the psychological or physical impacts of air pressure on the human body during analysis. Since our bodies are constantly resisting air pressure by the air we breathe and the air within our blood and organs we are affected by dramatic shifts in pressure, for example the popping of ones ears, aching joints, or headaches. Although not calculated data numerically, it is of interest to see if different air pressures of the room have a direct effect on the human body.

_Notes:

• Air moves from areas of higher pressure to areas of lower pressure through any available openings in building walls, floors, doors, windows, and air circulation systems.; it also produces winds.
• Air will move until the pressures inside and outside are equal. The air pressure differences are commonly caused by winds and unbalanced air circulation systems.
• Gay- Lussac’s Law – the pressure of a fixed mass and volume is directly proportional to temperature. In other words, in order to increase room air temperature, one must seal and heat the area.
• The density of dry air can be calculated using the ideal gas law, expressed as a function of temperature and pressure: p = P/R*T, where p is the air density, P is absolute pressure, R is the specific gas constant for dry air, and T is absolute temperature.
• Most obvious relationship to the human body is the discomfort in ears, headache and pain in joints.
• At 188.67m (618feet), the standard barometric pressure is 99kPa (744mmHg), which is the altitude of the city of Buffalo.  This means that there is 98% of the oxygen available at sea level.
• High pressure will make the balloon seal dip causing the straw go up. Low pressure will make the balloon puff up causing the straw to go down.

Sources: http://www.factmonster.com/ipka/A0769510.html

http://www.sciencecompany.com/barometric/barometer.htm

http://www.islandnet.com/~see/weather/eyes/barometer2.htm

http://www.srh.weather.gov/srh/jetstream/atmos/pressure.htm

http://www.ciese.org/curriculum/weatherproj2/en/docs/barometer.shtml

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