Question

(a) What are the common units of pressure? (b) How are they related?

Short answer

Common units of pressure include Pascal (Pa), pounds per square inch (psi), atmospheres (atm), bar, and millimeters of mercury (mmHg or torr). They relate to each other in the following way: 1 atm = 101325 Pa = 14.696 psi = 760 mmHg = 1.01325 bar.

Step-by-step solution

Listing Common Units of Pressure

The common units of pressure include Pascal (Pa), pounds per square inch (psi), atmospheres (atm), bar, and millimeters of mercury (mmHg or torr).

Relating The Units

1 Pascal (Pa) is the standard unit of pressure in the International System of Units (SI). Here are the conversions: \n 1 atm = 101325 Pa \n 1 atm = 14.696 psi \n 1 atm = 760 mmHg \n 1 atm = 1.01325 bar. \nSo, these units can be converted into one another using these equivalence relations.

Key concepts

Understanding Pascal as a Unit of Pressure

The Pascal (Pa) is the standard unit of pressure in the International System of Units (SI). It is named after the French mathematician, physicist, and inventor Blaise Pascal. When we measure pressure, we're looking at the force applied per unit of area. Specifically, one Pascal is defined as the pressure of one newton exerted over an area of one square meter.

This unit might seem small because pressures we experience daily, like atmospheric pressure or the pressure in car tires, are generally much larger than a single Pascal. Due to its relatively small magnitude, Pascal is often used with prefixes to describe everyday pressures: kilopascals (kPa) for thousands of Pascals, and megapascals (MPa) for millions of Pascals. These are more practical for real-world applications.

When talking about pressure in various scientific contexts, such as in physics and engineering, the use of Pascal provides a clear, measurable standard that is internationally recognized and widely used.

Atmospheres as a Measure of Pressure

The term 'atmosphere' (atm) originally referred to the pressure exerted by Earth's atmosphere at sea level. One standard atmosphere is equal to the pressure that can support a column of mercury 760 millimeters high in a mercury barometer at 0°C.

While not an SI unit, the atmosphere is commonly used in fields like meteorology, oceanography, and aviation. It serves as a point of reference for what we would consider 'normal' atmospheric pressure, hence the term standard atmosphere. It is also easier for people to relate to, as it was derived from an observable phenomenon.

Due to its relatability and significance in simulating average sea-level conditions, especially in gas law calculations, the atmosphere unit has remained in use for a variety of scientific and industrial purposes.

Converting Pressure Units

Understanding pressure conversions is essential for solving problems across different contexts and disciplines that may use varying pressure units. Conversions allow us to translate one set of pressure measurements to another, maintaining the accuracy and relevance of the data.

As seen in our example, 1 atmosphere can be converted to various other units: 1 atm = 101325 Pa 1 atm = 14.696 psi 1 atm = 760 mmHg 1 atm = 1.01325 bar

Conversions like these require memorization or access to conversion factors. However, once understood, they enable us to understand and communicate pressure information, whether it's checking the weather forecast or calibrating instruments for scientific research. In practical application, simple proportions can be used for converting one unit of pressure into another, or one can use online calculators and apps designed specifically for unit conversion to streamline the process.