The pressure outside a jet plane flying at high altitude falls considerably below atmospheric pressure at sea level. The air inside the cabin must therefore be pressurized to protect the passengers. What is the pressure (in atmosphere) in the cabin if the barometer reading is \(688 \mathrm{~mm}\) of \(\mathrm{Hg}\) ? (a) \(0.905 \mathrm{~atm}\) (b) \(6.88\) atm (c) \(9.05 \mathrm{~atm}\) (d) data, insufficient

Atmospheric pressure, often called air pressure, is the force exerted on a surface by the weight of the air above it. As one ascends in altitude, such as when flying in a jet plane, the atmospheric pressure decreases because there is less air above to exert downward force. Inside an aircraft cabin, maintaining a stable atmospheric pressure akin to sea level conditions is crucial for passenger comfort and safety.

A barometer is an instrument used to measure atmospheric pressure. Different types of barometers include mercury, aneroid, and digital barometers. A mercury barometer measures pressure in millimeters of mercury (mm Hg) and indicates the height of a mercury column that the air pressure can support.

To protect passengers from the low pressure at high altitudes, aircraft cabins are deliberately pressurized. If a barometer inside the cabin reads '688 mm Hg', this figure is below the standard atmospheric pressure but still within a range considered safe for passengers. Thus, understanding atmospheric pressure plays a crucial role in aeronautics and weather forecasting.

Standard atmospheric pressure, or simply standard pressure, is defined as the pressure exerted by the weight of the atmosphere at sea level under standard conditions. It serves as a reference point to determine if other pressure readings are higher or lower than usual everyday conditions on Earth's surface.

The universally accepted standard atmospheric pressure is approximately 760 mm Hg or 1013.25 hectopascals (hPa) or 29.92 inches of mercury. It is also equivalent to one atmosphere (1 atm), which is a unit of pressure commonly used in chemistry and physics. Reference to the standard pressure is essential when studying weather patterns, calibrating barometers, and designing pressurized systems such as those in aircraft cabins.

Converting pressure units is fundamental in science and engineering as it allows comparison and understanding of pressure readings in different units. The conversion from millimeters of mercury (mm Hg) to atmospheres (atm) is especially common.

To convert mm Hg to atm, one would apply the conversion factor that equates 760 mm Hg to 1 atm since these values are equivalents of standard atmospheric pressure. The formula for conversion is: \[ \text{Pressure (atm)} = \frac{\text{Barometer Reading (mm Hg)}}{\text{Standard Pressure (mm Hg)}} \].

For example, if a barometer reads 688 mm Hg, the conversion to atmospheres would be \( \frac{688}{760} \approx 0.905 \text{ atm} \), making option (a) correct for the exercise given.