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Intro - Density - Pressure - Depth - Pascal - Archimedes - Continuity - Bernoulli - Solutions

Pressure

      When air molecules are added to a container they are free to wander throughout its entire volume, and in the course of their wandering they collide with one another and with the inner walls of the container. The collisions with the walls allow the air to exert a force against every part of the wall surface which we call Pressure. The pressure exerted by a fluid is defined as the magnitude of the force acting perpendicular to a surface divided by the area (A) over which the force acts:

Pressure = Force / Area
The SI unit is N/m2 = Pascal (Pa)

      A pressure of 1 Pascal is a very small amount. Many common situations involve pressures of approximately 100,000 pascals or 100 kPa which is also called 1 bar of pressure. Walking about on land, we are at the bottom of the Earth's atmosphere, which is a fluid and pushes inward on our bodies. This atmospheric pressure at sea level is given in a variety of units:

101.3 kPa = 1 atmosphere (atm) = 14.7 lb/in2

      This is a significant amount of pressure. In the following video, we place water in a can and then boil it. Once the drum is full of steam, we remove it from the burner and seal it off. We then place the drum in an ice water bath which will condense the water vapor in the can so that there will be virtually zero air pressure in the can. The atmospheric pressure then crushes the can.

      The pressure in a fluid is 120.0 kPa. How much force is applied to an area of 8.4 x 10-3 m2?