# EARTH SCIENCE LAB Barometric Pressure

### Pressure Measurements

Atmospheric or barometric pressure is the result of the weight of a column of air above a given location. The elements and compounds that comprise the atmosphere have mass, and therefore exert a force within a gravitational field, i.e. weight. The amount and density of the atmosphere will determine the atmospheric pressure. The greater the height of the column of air or the greater its density, the higher the pressure will be. Conversely, a short column of air or a lower density will result in lower pressure.

As you have learned in previous labs, we unfortunately live in a country which insists on using the outdated and inconsistent English system of measurements. To equate measurements of pressure in English to Metric units requires converting one unit to another.

1 in. Hg = 33.8639 mb
1 in. Hg = 25.4 mm Hg
1 mm Hg = 0.0393701 in. Hg
1 mm Hg = 1.33322 mb
1 mb = 0.02953 in. Hg
1 mb = 0.750062 mm Hg

Fill in the table below by converting the following English and Metric pressure units using the conversion formulas given below. Report all answers to 2 decimal places.

1. Complete the following table of barometric pressure conversions. Report all values to 2 decimal places.
19.63 inches of Hg = millimeters of Hg
25.57 inches of Hg = millimeters of Hg
30.01 inches of Hg = millibars
29.85 inches of Hg = millibars
550.00 millimeters of Hg = inches of Hg
725.25 millimeters of Hg = inches of Hg
789.50 millimeters of Hg = millibars
635.75 millimeters of Hg = millibars
985.00 millibars inches of Hg
972.00 millibars inches of Hg
1001.00 millibars millimeters of Hg
1015.00 millibars millimeters of Hg

2. Using the pressure-elevation equation from your lab manual and given the elevation (h), calculate the atmospheric pressure (P). Report all values to 2 decimal places.
350 m = millibars
785 m = millibars
1120 m = millibars
1560 m = millibars
2597 m = millibars
3001 m = millibars
4596 m = millibars
6500 m = millibars

3. On the linked map, draw the isobars for every 4 millibars of pressure starting at 1000 mb (1000 mb, 1004 mb, 1008 mb, 1012 mb, etc.). On the map, due to space imitations, only the last two digits of the millibar pressure has been indicated. For example, 1000 mb would appear as 00, 1020 mb would appear as 20, and 995 mb would appear as 95. Draw each isobar line to just past the edge of the continent.