13 Fluids
• density
• pressure in a fluid
• buoyancy and archimedes’ principle
• Fluids in motion
• Hk: 21, 31, 33, 41, 43, 55.
Density
• = mass/volume
• SI Unit: kg/m3
• common unit: g/cm3
• 1,000 kg/m3 = 1 g/cm3
Pressure, p
• p = force/area
• Unit: pascal, Pa
• 1 Pa = 1N/m2.
• Example: 100N applied to 0.25m2. Pressure = 100/0.25 = 400N/m2.
Pascal’s Principle
AdF
AdFMA
Bulk Modulus
• B = -P/(V/V)
• compressibility = 1/B
• liquids have large B
• gasses have smaller B
Depth and Fluid Pressure• P = Po + gd
• P is the pressure at depth d.
• Po is the pressure at the fluid surface
• is the fluid density
• Example: increase in pressure at a depth of 1m in water = (1,000)(9.8)(1.0) Pa
Buoyancy and Archimedes’ Principle
8
vv AA
9
At same velocity: lower height fluid is at greater pressureAt same height: faster moving fluid = less pressure
Summary
• Density = mass/volume
• pressure in a fluid varies with depth
• Buoyant force = weight of displaced fluid
• Fluids in motion
• /
Gauge Pressure is Differential Pressure
)76.0)(/8.9)(/600,13(0 3 mkgNmkgghP
Barometer
13
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