Pressure
Is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also called gage pressure) is relative to the ambient pressure. Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square meter (N/m2); similarly, the pound-force per square inch (psi, symbol lbf/in2) is the traditional unit of pressure in the imperial and U.S. customary systems. Pressure may also be expressed in standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as 1⁄760 of this. Manometric units such as the centimeter of water, millimeter of mercury, and inch of mercury are used to express pressures in terms of the height of a column of a particular fluid in a manometer [Knight, Randall, p.1183].
The perpendicular force per unit area, or the stress at a point within a confined fluid. The pressure exerted on a floor by a 42-pound box, the bottom of which has an area of 84 square inches, is equal to the force divided by the area over which it is exerted; i.e., it is one-half pound per square inch. The weight of the atmosphere pushing down on each unit area of Earth’s surface constitutes atmospheric pressure, which is about 15 pounds per square inch at sea level. In SI units, pressure is measured in pascals; one pascal equals one newton per square meter. Atmospheric pressure is close to 100,000 pascals. The pressure exerted by confined gas results from the average effect of the forces produced on the container walls by the rapid and continual bombardment of the significant number of gas molecules. The absolute pressure of a gas or liquid is the total pressure it exerts, including the effect of atmospheric pressure. An absolute zero pressure corresponds to space or a vacuum [Online Encyclopaedia Britannica].
The force that a liquid or gas produces when it presses against an area:
- The gas is stored under pressure (in a container that keeps it at a higher pressure than it would usually have) [Cambridge Online Dictionary].
Knight, Randall, D. (2007). Physics for Scientists and Engineers: A Strategic Approach (2nd ed.). San Francisco: Pearson Addison Wesley.
Pressure. Online Encyclopaedia Britannica. Retrieved from: https://www.britannica.com/science/pressure
Pressure. Cambridge Online Dictionary. Retrieved from: https://dictionary.cambridge.org/dictionary/english/pressure