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Pressure Notes
Back of the examples for Pressure WS #1 is
homework
1. Copy the examples into your notes.
2. The solutions to the examples are at the end.
3. Start on your homework.
4. Bring your textbook to class on January 13, 2014.
5. Be prepared to ask specific questions on
Wednesday after the quiz.
Pressure and
Pascal’s Principle
P = F/A
P1 =P2
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Review:
Properties of Static Fluids
The properties useful for describing a static fluid at a
point are:
Density: Mass of a given volume of the substance
divided by its volume, given by
r = Density
m
r
V
Unit: metric unit is kg/m3, often expressed in g/cm3.
Be able to do the conversions from g/cm3 to kg/m3.
Review:
Properties of Static Fluids (cont.)
 The following table lists the densities of some
common substances in kg/m3.
Material
Water
Iron
Mercury
Ice
Density (kg/m3)
1000
7900
13600
917
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Pressure formula is:
P = F/A
Pressure:
 Definition: Force exerted by a fluid at a point divided by the area of the
surface, given by P = F/A
 Unit: The metric unit is Pa = N/m2, given the name Pascal.
 The following figure depicts the calculation of pressure in the case of a
small vertical cylinder filled with a fluid and with its base at the point.
Measurement of Atmospheric Pressure
The atmospheric pressure at any point can be
measured using a simple device called a mercury
barometer that works on the basis of
P=hrg
where, P is the pressure, h is the depth of the fluid, r is the
density of the fluid, and g is the acceleration due to gravity. The
following figure depicts a mercury barometer.
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Pascal’s Principle
P 1 = P2
Statement: When pressure is applied to an enclosed static
fluid, the pressure is transmitted undiminished to every part
of the fluid. This means the pressure is constant at all points.
Example: A device called the hydraulic press or lever works on
Pascal’s principle, as shown in the following figure:
P1 = P2
F1/A1 = F2/A2 A1
F1
F2
A2
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