Final answer:
Atmospheric pressure decreases by about 1 inch of mercury for each 1000 feet increase in altitude. For example, at sea level, the atmospheric pressure is about 760 mmHg, while on the summit of Mount Everest, the atmospheric pressure is around 253 mmHg.
Step-by-step explanation:
Because the air gets less dense and has fewer molecules, atmospheric pressure drops as one rises in altitude. In a barometer, the atmospheric pressure at sea level is sufficient to support a mercury column that measures about 760 mm. The mercury column, however, decreases to about 630 mm at higher elevations, such as Denver, Colorado, which is at about 5280 feet or 1609 meters. With this data, we can calculate that for every 1000 feet of elevation, the pressure drops by about 1 inch of mercury. Consequently, the atmospheric pressure tends to drop by about 1 inch of Hg (inches of mercury) for every 1000 feet of altitude gain.