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Pressure; Pascal’s Principle

Pressure; Pascal’s Principle. PRESSURE OF A FLUID. pressure = height of mercury column . air pressure. Barometer. Gauge pressure – pressure above the atmospheric pressure. absolute (total) pressure = gauge pressure + atmospheric press. Pressure is produced by the

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Pressure; Pascal’s Principle

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  1. Pressure; Pascal’s Principle

  2. PRESSURE OF A FLUID pressure = height of mercury column air pressure Barometer

  3. Gauge pressure – pressure above the atmospheric pressure. absolute (total) pressure = gauge pressure + atmospheric press.

  4. Pressure is produced by the weight of the fluid above the surface.

  5. force pressure = ------ area weight of fluid = ---------------- area mg = ----- area density · volume · g = ------------------------- area density · (area · height) · g = -------------------------------- area

  6. pressure = density · height · g P = ρhg gauge pressure P = ρhg + P0 absolute pressure SI units: pressure: N/m2 = Pascals (Pa) density: kg/m3 height (depth): m

  7. Standard atmospheric pressure 760 mm Hg ≈ 30 in Hg Calculate 1 atm in Pascals P = ρgh ρHg = 13.6 x 103 kg/m3 g = 9.8 N/kg h = 0.760 m P = 1.013 x 105 Pa

  8. Why does a barometer use mercury and not water? If p = 1 atmosphere = 1.013 x 105 Pa ρ = 1.00 g/cm3 = 1.00 x 103 kg/m3 Find height. 10.3 m

  9. Pressure of fluid depends on depth.

  10. Pressure does not depend on volume, only on height (depth). “Water seeks its own level”

  11. More pressure at greater depth

  12. Measure blood pressure at upper arm same height as heart

  13. Pascal’s Principle – The pressure in an enclosed fluid is constant throughout the fluid. p1 = p2 F1 F2 --- = --- A1 A2

  14. 1 N ? A = 1 cm2 A = 50 cm2 p1 = p2 1 N F2 ------- = ------ 1 cm2 50 cm2 50 N

  15. If piston on left moves 10 cm, what distance does piston on right move? work1 = work2 F1 d1 = F2 d2 (1) (10) = (50) d2 0.2 cm

  16. Hydraulic lift

  17. Area of brake cylinder > area of brake line force of brake cylinder > force of brake pedal

  18. hydrostatic pressure

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