—pressureless, adj./presh"euhr/, n., v., pressured, pressuring.n.1. the exertion of force upon a surface by an object, fluid, etc., in contact with it: the pressure of earth against a wall.3. Meteorol. See atmospheric pressure.4. Elect. See electromotive force.5. the state of being pressed or compressed.6. harassment; oppression: the pressures of daily life.7. a constraining or compelling force or influence: the social pressures of city life; financial pressure.8. urgency, as of affairs or business: He works well under pressure.9. Obs. that which is impressed.v.t.10. to force (someone) toward a particular end; influence: They pressured him into accepting the contract.11. pressurize.[1350-1400; ME (n.) < L pressura. See PRESS1, -URE]
* * *IPerpendicular force per unit area, or stress at a point within a confined fluid.A solid object exerts pressure on a floor equal to its weight divided by the area of contact. The weight of the Earth's atmosphere on the surface constitutes atmospheric pressure, which varies from place to place but always decreases with altitude. The pressure exerted by a confined gas results from the average effect of the forces produced on the walls of the container by the continual, numerous collisions by gas molecules. Hydrostatic pressure is the stress, or pressure, exerted equally in all directions at points within a confined fluid. Lithostatic pressure is the stress exerted on a body of rock in the Earth's crust by surrounding rock, which increases with depth below the surface. The SI unit of pressure is the pascal (Pa), which is equal to one newton of force per square metre.II(as used in expressions)
* * *▪ physicsin the physical sciences, 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 Earth's atmosphere pushing down on each unit area of the Earth's surface constitutes atmospheric pressure, which at sea level is about 15 pounds per square inch. In SI units, pressure is measured in pascals; one pascal equals one newton per square metre. Atmospheric pressure is close to 100,000 pascals.The pressure exerted by a confined gas results from the average effect of the forces produced on the container walls by the rapid and continual bombardment of the huge number of gas molecules. Absolute pressure of a gas or liquid is the total pressure it exerts, including the effect of atmospheric pressure. An absolute pressure of zero corresponds to empty space or a complete vacuum.Measurement of pressures by ordinary gauges on Earth, such as a tire-pressure gauge, expresses pressure in excess of atmospheric. Thus, a tire gauge may indicate a pressure of 30 pounds (per square inch), the gauge pressure. The absolute pressure exerted by the air within the tire, including atmospheric pressure, is 45 pounds per square inch. Pressures less than atmospheric are negative gauge pressures that correspond to partial vacuums.Hydrostatic pressure is the stress, or pressure, exerted equally in all directions at points within a confined fluid (liquid or gas). It is the only stress possible in a fluid at rest. See Pascal's principle.Lithostatic pressure, the stress exerted on a body of rock by surrounding rock, is a pressure in the Earth's crust somewhat analogous to hydrostatic pressure in fluids. Lithostatic pressure increases with depth below the Earth's surface.
* * *