Pressure is a fundamental physical quantity that describes the force exerted perpendicular to a surface per unit area. Understanding pressure and its measurement is significant across various scientific disciplines and in many aspects of daily life. The standard international (SI) unit for measuring pressure is the Pascal (Pa), which provides a consistent and universal measure for this important physical property, ensuring clarity and precision in scientific and engineering communications worldwide.
Defining the Pascal Unit
The Pascal (Pa) is defined as one Newton per square meter (1 Pa = 1 N/m²). This means that a pressure of one Pascal results when a force of one Newton is applied perpendicularly over an area of one square meter. A Newton is the SI unit of force, representing the force required to accelerate one kilogram of mass at one meter per second squared. A square meter is the SI unit for area.
A single Pascal represents a relatively small amount of pressure, roughly equivalent to the pressure exerted by a dollar bill resting flat on a surface. Because of its small magnitude, pressure is often expressed using multiples of the Pascal in practical applications:
Kilopascal (kPa): 1,000 Pascals (1 kPa = 10³ Pa)
Megapascal (MPa): 1,000,000 Pascals (1 MPa = 10⁶ Pa)
Gigapascal (GPa): 1,000,000,000 Pascals (1 GPa = 10⁹ Pa)
Hectopascal (hPa): 100 Pascals (1 hPa = 100 Pa)
The unit is named in honor of Blaise Pascal, a 17th-century French mathematician and physicist. He made significant contributions to the understanding of fluids, pressure, and the principles of hydrodynamics and hydrostatics. His experiments, including those with barometers, helped establish foundational theories about fluid behavior and atmospheric pressure.
Where You Encounter Pascal
The Pascal and its multiples are widely used in various fields to quantify pressure. In meteorology, for instance, atmospheric pressure is commonly reported in hectopascals (hPa). This unit replaced the older millibar, with 1 hPa being numerically equal to 1 millibar, making the transition seamless for weather reporting. Standard atmospheric pressure at sea level is approximately 1013.25 hPa. Changes in these readings can indicate shifts in weather patterns, with falling pressure often signaling approaching low-pressure systems and potential stormy weather, while rising pressure suggests stable conditions.
In industrial and engineering applications, Pascals are used to measure various types of pressure. Hydraulic and pneumatic systems, which rely on the force exerted by fluids or compressed air, often utilize kilopascals (kPa) or megapascals (MPa) due to the higher pressures involved. For example, the pressure within a pneumatic system is typically measured in kilopascals. In materials science and engineering, the strength, stiffness, and compressive strength of materials are frequently measured in megapascals (MPa) or gigapascals (GPa). Concrete used in construction might have a compressive strength in the range of 30 to 50 MPa, while reinforcing steel can have a yield strength of 400 to 500 MPa.
Although blood pressure is typically measured in millimeters of mercury (mmHg), these values can be converted to Pascals, highlighting the unit’s universal applicability in scientific contexts. Underwater pressure, which increases with depth, can also be expressed in Pascals or atmospheres, demonstrating how the unit applies to both gases and liquids in diverse environments.