Final answer:
In physics, pressure is measured in various units such as Pascal, atmospheres (atm) and millimeters of mercury (mmHg). Atmospheric pressure at sea level is approximately 1 atm, which is equal to a column height of 760 mm Hg. The unit torr is also used to measure pressure, with 1 torr being equal to 1 mm Hg.
Step-by-step explanation:
The proper SI unit for pressure is the Pascal (Pa), where 1 Pa = 1 kg m-1 s-2. In chemistry, however, it is more common to measure pressure in terms of atmospheres (atm), where 1 atm is atmospheric pressure at sea level, or 1 atm = 14.7 pounds per square inch (1 atm = 101,325 Pa). Atmospheric pressure is typically measured using a device called a barometer. A simple mercury barometer (also called a Torricelli barometer, after its inventor) consists of a glass column, about 30 inches high, closed at one end and filled with mercury. The column is inverted and placed in an open, mercury-filled reservoir. The weight of the mercury in the tube causes the column to drop to the point that the mass of the mercury column matches the atmospheric pressure exerted on the mercury in the reservoir. The atmospheric pressure is then read as the height of the mercury column. Again, working at sea level, 1 atmosphere is exactly equal to a column height of 760 mm of mercury. The units for the conversion are 1 atm = 760 mm Hg, and this is an exact relationship with regard to significant figures. The unit torr (after Torricelli) is sometimes used in place of mm Hg.