Atmospheric Pressure and Gauge Pressure

Pressure is measured in newtons per square meters, N / m²; this is known as a pascal, Pa.

1 pascal = 1 Pa = 1 [ N / m² ]

Other units:

1 atm = 1.013 x 10⁵ Pa

1 bar = 100 kPa = 1 x 10 ⁵ Pa

( 1 atm = 1.013 bar)

1 mm Hg = 133 Pa

1 atm = 760 mm Hg

This is also known as a Torr, named for Torrecelli,

1 Torr = 1 mm Hg

1 atm = 760 Torr

What is the pressure P_C in this chamber?

We may measure it in mm Hg. That is really the difference between atmospheric pressure P_o and the pressure P_C in the chamber.

This term on the right is called gauge pressure. Absolute pressure is gauge pressure plus atmospheric pressure,

 

Pressure			Pascal's Principle
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(c) 2002, Doug Davis; all rights reserved