Question

What a re the units for measuring air pressure? a. \(\mathrm{mm} \mathrm{Hg}\) b. \(\mathrm{mm}\) O2 c. Percent \(\mathrm{Hg}\) d. Percent \(\mathrm{O} 2\)

Short answer

a. mm Hg b. mm O2 c. Percent Hg d. Percent O2 Answer: a. mm Hg

Step-by-step solution

Identifying the unit for measuring air pressure

Among the given options, we need to find the unit commonly used for measuring air pressure. The choices are: a. mm Hg b. mm O2 c. Percent Hg d. Percent O2

Select the correct unit for measuring air pressure

From the options, we can see that option (a) \(\mathrm{mm} \mathrm{Hg}\) is the correct unit for measuring air pressure. The other units are not commonly used to represent air pressure. Therefore, the correct answer is (a) \(\mathrm{mm} \mathrm{Hg}\).

Key concepts

mm Hg

The unit 'mm Hg', also known as millimeters of mercury, is a common way to express atmospheric pressure. It originates from the use of mercury in barometers, where the height of the mercury column responding to the surrounding air pressure is measured in millimeters.

To understand 'mm Hg', it is essential to go back to the traditional barometer, a device typically consisting of a glass tube closed at one end and open at the other, and partially filled with mercury. The open end is immersed in a mercury reservoir. Air pressure is determined by the weight of the air above the reservoir pressing down on the mercury surface, causing the mercury to rise in the tube. The height to which the mercury rises can then be measured in millimeters. This height, in turn, is a direct indication of the atmospheric pressure.

How to Read a Barometer

Traditionally, when the barometer reads 760 mm Hg, the atmospheric pressure is said to be at sea level standard, which is equivalent to 1 atmosphere (atm). Changes in the height of the mercury column indicate changes in air pressure, with higher columns representing higher pressure and vice versa.

Atmospheric Pressure

Atmospheric pressure is the force per unit area exerted against a surface by the weight of the air above that surface in the Earth's atmosphere. It plays a crucial role in meteorology and is a fundamental aspect of weather patterns and climatic conditions.

At sea level, the standard atmospheric pressure is 101,325 Pascals (Pa), which is equivalent to 1 atm or 760 mm Hg. However, this value decreases with elevation, meaning that the higher you go, the lower the atmospheric pressure, because there is less air mass above you exerting downward force.

Importance of Atmospheric Pressure

Atmospheric pressure affects everything from the boiling point of water to the ability of living organisms to breathe. Changes in atmospheric pressure are indicative of forthcoming weather changes; for example, falling pressure usually signifies that bad weather is approaching, whereas rising pressure indicates good weather.

Units of Pressure

Pressure is defined as the force exerted on a unit area and can be measured using various units. In addition to 'mm Hg', atmospheric pressure can be expressed in several other units such as Pascals (Pa), atmospheres (atm), and pounds per square inch (psi).

The Pascal (1 Pa = 1 N/m²) is the Système International (SI) unit of pressure and is widely used in science and engineering. One atmosphere (1 atm) is defined as being exactly equivalent to 101,325 Pa. For application within various fields, units like Pascals can be too small, hence kilopascals (kPa) are often employed. Psi is mainly used in the United States and denotes the pressure resulting from a one-pound-force applied to an area of one square inch.

Conversion Between Pressure Units

To convert between these units, one must use specific conversion factors – for instance, 1 atm equals 101.3 kPa, around 14.7 psi, or exactly 760 mm Hg. The choice of unit often depends on the field of study, regional preferences, and the context of the measurement.