Summary
- Pressure (P) is the ratio of normal force (F) to area (A).
- Although both force and area are vectors, pressure is a scalar quantity and has no direction.
- Pressure is a way to describe force in a region of a continuous system.
- Units
- The SI unit of pressure is the pascal [Pa = N/m2 = kg/ms2].
- One hundred thousand pascals are sometimes called a bar [100,000 Pa = 1 bar].
- The unit atmosphere is101,325 Paby definition.
- Absolute vs. Gauge
- The pressure of a region, as defined above, is its absolute pressure (P).
- The pressure difference between a system and its environment (P0) is known as gauge pressure (Pg).
- Stevin's law: The pressure (P) in a uniform fluid at rest…
- is equal to the weight of a column of fluid divided by the area on which it rests, so that it…
- increases uniformly with depth (h)
- is directly proportional to the density of the fluid (ρ)
- depends on the surface pressure (P0)
- acts equally in all directions and therefore…
- exerts a net force perpendicular to any surface that it contacts
- Pascal's principle: Pressure changes applied to the surface of an enclosed fluid are transmitted evenly throughout the fluid.
- Hydraulics increase force, but
- decrease distance (since energy is conserved)
