Pressure

Pressure is the amount of force applied normal to a surface divided by the area of that surface. As an example of varying pressures, a finger can be pressed against a wall without making any lasting impression; however, the same finger pushing a thumbtack can easily damage the wall. Although the force applied to the surface is the same, the thumbtack applies more pressure because the point concentrates that force into a smaller area.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

More formally, pressure (symbol: p) is defined as the magnitude of the normal force divided by the area over which the normal force acts.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

:p = F / A

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

where p is the pressure, F is the normal force, and A is the area. Pressure is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point. Unlike stress, pressure is defined as a scalar quantity.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The gradient of pressure is force density.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Pressure is sometimes measured, not as an absolute pressure, but relative to atmospheric pressure; such measurements are sometimes called gauge pressure. An example of this is the air pressure in a car tire, which might be said to be "220 kPa," but is actually 220 kPa above atmospheric pressure. Since atmospheric pressure at sea level is about 100 kPa, the absolute pressure in the tire is therefore about 320 kPa. In technical work, this is written "a gauge pressure of 220 kPa." Where space is limited, such as on gauges, name plates, graph labels, and table headings, the use of a modifier in parentheses, such as "kPa (gauge)" or "kPa (absolute)," is permitted. In non-SI technical work, a gauge pressure is sometimes written as "32 psig," though the other methods explained above that avoid attaching characters to the unit of pressure are preferred. 1

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In the human body, baroreceptors monitor blood pressure.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

"Pressure is a scalar quantity, but teachers and authors do not appear to believe this in their hearts." (McClelland, 1987)

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Normal: Normal may refer to:...

Force: In physics, a force is an external cause responsible for any change of a physical system. For instance, a person holding a dog by a rope is experiencing the force applied by the rope on his hand, and the cause for its pulling forward is the force exercised by the rope. The kinetic expression of th...

Area: This article explains the meaning of area as a physical quantity. The article area (geometry) is more mathematical....

Pressure related Images and Photos (experimental)

Pressure Points	Pier Pressure	Pressure - Balloon Penetrating Illusion	Withings Blood Pressure Monitor
Escape Under Pressure (DVD)	MythBusters Power of Air Pressure Science Kit