13 Fluids

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13 Fluids

• density
• pressure in a fluid
• buoyancy and archimedes principle
• Fluids in motion
• Hk 21, 31, 33, 41, 43, 55.

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Density

• r mass/volume
• SI Unit kg/m3
• common unit g/cm3
• 1,000 kg/m3 1 g/cm3

3
Pressure, p

• p force/area
• Unit pascal, Pa
• 1 Pa 1N/m2.
• Example 100N applied to 0.25m2. Pressure
  100/0.25 400N/m2.

4
Gauge Pressure is Differential Pressure
5
Bulk Modulus

• B -DP/(DV/V)
• compressibility 1/B
• liquids have large B
• gasses have smaller B

6
Depth and Fluid Pressure

• P Po rgd
• P is the pressure at depth d.
• Po is the pressure at the fluid surface
• r is the fluid density
• Example increase in pressure at a depth of 1m in
  water (1,000)(9.8)(1.0) Pa

7
Buoyancy and Archimedes Principle
8
Force Diagrams
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Summary

• Density mass/volume
• pressure in a fluid varies with depth
• Buoyant force weight of displaced fluid
• Fluids in motion
• /

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11
Pascals Principle
Example A2/A1 100 F2/F1 100
12
Barometer