Question

What are the common units used to measure pressure? Which unit is an experimental unit derived from the device used to measure atmospheric pressure?

Short answer

The common units used to measure pressure are Pascal (Pa), atmosphere (atm), Torr, and pound per square inch (psi). They can be converted using the following factors: 1 atm = \(101,325\) Pa, 1 atm = 760 Torr, and 1 atm = 14.696 psi. The Torr is the experimental unit derived from the device used to measure atmospheric pressure, specifically the mercury barometer invented by Evangelista Torricelli. 1 Torr is defined as the pressure experienced at the base of a column of mercury exactly 1 millimeter in height at 0 degrees Celsius under Earth's standard gravitational force.

Step-by-step solution

Identify common units used to measure pressure

The common units used to measure pressure are Pascal (Pa), atmosphere (atm), Torr, and pound per square inch (psi). Below are the corresponding conversion factors: 1 atm = \(101,325\) Pa 1 atm = 760 Torr 1 atm = 14.696 psi

Identify the experimental unit derived from the device

Torr is the experimental unit derived from the device used to measure atmospheric pressure. This unit is named after the Italian scientist Evangelista Torricelli, who invented the mercury barometer in 1643. The barometer measures atmospheric pressure by balancing the weight of the mercury column against the pressure of the atmosphere. 1 Torr is defined as the pressure experienced at the base of a column of mercury exactly 1 millimeter in height at 0 degrees Celsius under Earth's standard gravitational force.

Key concepts

Pascal

Understanding pressure measurement starts with the Pascal (Pa), the standard unit in the International System of Units (SI). It represents the force of one newton acting on a surface area of one square meter. In less technical terms, imagine a small apple applying its weight evenly over a square meter; that pressure exerted is approximately one pascal.

Especially in scientific contexts, pascals are invaluable because they provide an accurate and small scale unit for pressure - although they can result in large numerical values for common pressures. For instance, atmospheric pressure at sea level is about 101,325 Pa. To put it into context, an averaged-sized balloon might exert a pressure of around 1,000 Pa when pressed against your hand.

Atmosphere Unit

The atmosphere unit (atm) connects directly to our daily experience, as it is based on the average pressure at sea level on Earth. One atmosphere is equivalent to the pressure exerted by a 760 mm column of mercury in a mercury barometer at 0 degrees Celsius. Practically, one atmosphere serves as a reference point; for example, deep sea divers may use atmospheres to report the pressure they're subjected to under water.

A standard atmosphere is approximately equivalent to 101,325 Pa, which establishes a convenient round figure for understanding atmospheric conditions without dealing with large numbers. This makes it especially easy for students to grasp environmental and geological pressure conditions where the pascal might be excessively precise.

Torr

The Torr is a legacy non-SI unit of pressure named after Evangelista Torricelli, a pioneering Italian scientist. This unit directly stems from the operation of the mercury barometer, a device he invented to measure atmospheric pressure. One Torr is equivalent to the pressure exerted at the base of a column of mercury precisely 1 millimeter high.

Torr remains in widespread use particularly in fields like vacuum physics and engineering due to its practical connection to the barometric measurement method. In terms of equivalences, there are 760 Torr in one atmosphere which aligns with the height in millimeters of the mercury column sustained by the Earth's atmospheric pressure at sea level. Interestingly, one millimeter of mercury (mmHg) is commonly used in medical blood pressure measurements, which is numerically identical to the Torr.

Pound per Square Inch

The pound per square inch (psi) is a unit of pressure commonly used in the United States and other countries still working with the Imperial system. This unit describes the amount of force in pounds exerted on one square inch of area. Its relevance stems from common real-world applications, like tire pressure in vehicles, or pressure in hydraulic systems.

A helpful comparison for psi uses familiar items: one psi is about the pressure exerted by a basketball on the palm of your hand. For conversions, as mentioned before, one atmosphere is approximately 14.696 psi. This illustrates why the psi is so prevalent in everyday life - it's based on familiar weights (pounds) and small manageable areas (inches), unlike pascals which can represent very large numbers for everyday pressures.