1. Physics 114 – Lecture 29 §10.4 Atmospheric Pressure and Gauge Pressure
Atmospheric pressure, PA, is, on average, at sea level,
PA = X 105 N/m2
Other units are used, for example, 1 bar = 1.00 X 105 N/m2,
see Table 10.2, p 261 in Giancoli
Study Example 10.4: finger holding water in a straw
Gauge Pressure
Pressure above atmospheric pressure, e.g., pressure measured by a tire gauge and many other gauges
P = PA + PG
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2. Physics 114 – Lecture 29 §10.5 Pascal’s Principle
Pascal’s Principle states that if an external pressure is applied to a confined fluid the pressure at all points within the fluid is increased by the amount of the external pressure.
E.g., hydraulic jack
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3. Physics 114 – Lecture 29
§10.6 Measurement of Pressure; Gauges and the Barometer
Open tube manometer
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4. Physics 114 – Lecture 29
Aneroid gauge
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5. Physics 114 – Lecture 29
Tire gauge
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6. Physics 114 – Lecture 29
Atmospheric pressure is conveniently measured with a barometer, usually a mercury barometer
P = ρgh = (13.6 X 103 kg/m3) X 9.80 m/s2
X m = X 105 N/m2
= 1.00 atm
• This is often stated as:
PA = m of Hg (mercury)
= 76.0 cm of Hg = 760 mm of Hg
• Study Example suction
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7. Physics 114 – Lecture 29 §10.7 Buoyancy and Archimedes’ Principle
FB = F2 – F1
= ρgAh2 – ρgAh1
= ρgA Δh = ρgV
= mg (mass of fluid
displaced)
•Study Examples 10.6,
10.7, 10.8, 10.9,
10.10
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