Question

Give the value for standard atmospheric pressure in each of the following units: (a) millimeters of mercury (b) centimeters of mercury

Short answer

(a) 760 mmHg, (b) 76 cmHg.

Step-by-step solution

Understanding Standard Atmospheric Pressure

The standard atmospheric pressure at sea level is a constant value used for scientific calculations, often measured in different units like pascals, millimeters of mercury (mmHg), or inches of mercury (inHg). It represents the pressure exerted by the Earth's atmosphere on objects at sea level.

Converting to Millimeters of Mercury

At sea level, the standard atmospheric pressure is equal to 760 millimeters of mercury (mmHg). This is a widely recognized standard figure derived from historical measurements using mercury column barometers.

Converting to Centimeters of Mercury

To convert millimeters of mercury to centimeters of mercury, divide the value in millimeters by 10, since there are 10 millimeters in a centimeter. Therefore, 760 mmHg is equivalent to \( \frac{760}{10} = 76 \) centimeters of mercury (cmHg).

Key concepts

Pressure Units Conversion

Pressure is an important concept in physics and chemistry, especially when studying gases and weather systems. However, pressure can be measured in various units, much like length can be measured in meters or feet. Converting between pressure units is crucial to ensure scientific consistency and accuracy in calculations.

• Pascals (Pa): The SI unit of pressure, where 1 pascal is the pressure of 1 Newton per square meter.
• Millimeters of Mercury (mmHg): A traditional unit of pressure, often used in medicine and aviation.
• Inches of Mercury (inHg): Commonly used in aviation and meteorology in the United States.
• Atmospheres (atm): Used to express large pressures typically, where 1 atm is the pressure exerted by the weight of the Earth's atmosphere at sea level.

Converting between these units often involves knowing the standard equivalencies. This is vital, especially when comparing results from different scientific contexts or when applying the concepts in real-world applications such as weather forecasting or medical diagnostics. Using these conversions, we can express atmospheric pressure, or any other pressure, in a unit that makes the most sense for the application at hand.

Millimeters of Mercury

The millimeter of mercury, known by its symbol mmHg, is a traditional unit of pressure. It is derived from the use of a mercury barometer, where pressure is measured by the height of a column of mercury that the atmosphere can support.
One key aspect of using mmHg is its historical context. Unlike some abstract units, mmHg arose from practical measurements using liquid mercury. Mercury's density makes it particularly useful for barometers because even a small atmospheric pressure change results in a clear and easily readable change in the height of the mercury column.
At sea level, the standard atmospheric pressure is defined as 760 mmHg. This number isn’t arbitrary—it was established based on average observations and has been a benchmark for the standard atmosphere in scientific studies. It is important to accurately convert and understand this measurement when dealing with pressure-related problems in medicine, like blood pressure, or in scientific experiments that require precise pressure measurements.

Centimeters of Mercury

Centimeters of Mercury (cmHg) is another unit of pressure measurement, which is simply a larger scale of mmHg. It is used in some contexts where larger or simplified numbers are more convenient, such as in certain engineering calculations or when dealing with larger scales.
To convert from mmHg to cmHg, simply divide the millimeter value by 10. For example, the standard atmospheric pressure of 760 mmHg becomes 76 cmHg. This conversion is straightforward because there are 10 millimeters in a centimeter.
Understanding cmHg is also useful when comparing it to other units of atmospheric pressure. It is less frequently used than mmHg but can appear in specific technical contexts.
In conclusion, knowing how and when to make these conversions ensures clarity and consistency across different fields and applications, making it a valuable skill in both academic and professional settings.