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Chapter

PHY 1122 Chapter Notes -Hydrostatics, Atmospheric Pressure, Hydraulic Machinery


Department
Physics
Course Code
PHY 1122
Professor
Andrzej Czajkowski

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Fluid: liquid or gas
Fluid statics: study of fluids at rest in equilibrium
12.1 Density
Density ( )ρ = mass / Volume
oUnit: kg / m^3
Specific Gravity: ratio of material's density to the density of water (1000 kg/m^3)
oNo units
Average density
oHuman body (bones vs fat)
oAtmosphere
Useful for determining battery charge
Example 12.1 The Weight of a Roomful of Air
Q) Find mass and weight of air at 20C in a room w/ 4.0 m x 5.0 m floor and a ceiling 3.0 m high, and
the mass and weight of an equal volume of water.
A) V = (4.0)(5.0)(3.0) = 60 m^3
m(air) = (air)V = (1.20 kg/m^3)(60 m^3) =ρ 72 kg
w(air) = m(air)g = (72g)(9.8 m/s^2) = 700 N = 160 lb
m(water) = (water)V = (1000 kg/m^3)(60 m^3) =ρ 6.0 x 104 kg
w(water) = m(water)g = (6.0 x 10.4 kg)(9.8 m/s^2)
= 5.9 x 10^5 N = 1.3 x 10^5 lb = 66 tons
12.2 Pressure in a Fluid
Pressure (p) = dF(perp) / dA
oIf pressure is the same at all points of a finite plane then
o
p = F(perp) / A
oF(perp) = net normal force on one side of surface
oUnit: 1 pascal (Pa) = 1 N/m^2
o
1 bar = 10^5 Pa
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