Download gauge pressure. Why?

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pgs. 317 - 342
Calculate the pressure exerted by a fluid.
Explain Pascal’s Principle.
Calculate how pressure varies with depth in a
A measure of the force applied to a surface
per unit area
SI unit of pressure is the Pascal (Pa) = 1 N/m2
The pascal is a small amount of
At sea level, the pressure of the
atmosphere is 1.01x 105 Pa
This amount of air pressure is
the basis for another unit,
1 atm = 1.01 x 105 Pa
Atmospheric pressure is normally about
100,000 Pascals.
Differences in atmospheric pressure cause
winds to blow.
Low atmospheric pressure inside a
hurricane’s eye contributes to the severe
winds and the development of the storm
The force on a surface caused by
pressure is always normal (or
perpendicular) to the surface. This
means that the pressure of a fluid is
exerted in all directions, and is
perpendicular to the surface at every
Calculate the net force on an airplane window
if the cabin pressure is 90% of the pressure at
sea level and the external pressure is only
50% of that at sea level. The window is 0.43m
tall and 0.30m wide.
Applied pressure is transmitted equally
throughout a fluid
The small piston of a hydraulic lift has an area of
0.20 m2. A car weighing 1.20 x 104 N sits on a rack
mounted on the large piston. The large piston has an
area of 0.90 m2. How large a force must be applied to
the small piston to support the car?
P = ρgh
P: pressure (Pa)
ρ : density (kg/m3)
g: acceleration constant (9.81 m/s2)
h: height of liquid column (m)
This type of pressure is often called gauge
If the liquid is water, this is referred to as
pressure. Why?
hydrostatic pressure.
Absolute pressure is obtained by adding
the atmospheric pressure to the hydrostatic
Pressure varies with the depth of a fluid
Po = 1.01 x 105 Pa
Buoyant forces arise from the differences in
fluid pressure between the top and bottom of
an immersed object.
Pnet = Pbottom - Ptop
Atmospheric pressure is pressure from above
The weight of the air in the upper
portion of Earth’s atmosphere exerts
pressure on the layers below
Mercury barometer is commonly
used to measure atmospheric
Calculate the absolute pressure at an ocean
depth of 1.00 x 103 m. Assume that the
density of the water is 1.025 x 103 kg/m3 and
that P0 = 1.01 x 105 Pa.