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

2. 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 SI units: pressure: N/m 2 = Pascals (Pa) density: kg/m 3 height (depth): m P = ρhg + P 0 absolute pressure

7. Standard atmospheric pressure 760 mm Hg ≈ 30 in Hg Calculate 1 atm in Pascals P = ρgh ρ Hg = 13.6 x 10 3 kg/m 3 g = 9.8 N/kg h = 0.760 m P = 1.013 x 10 5 Pa

8. Pressure of fluid depends on depth.

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

10. More pressure at greater depth

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

12. Pascal’s Principle – The pressure in an enclosed fluid is constant throughout the fluid. p 1 = p 2 F 1 F 2 --- = --- A 1 A 2

13. Pascal’s Principle When force is applied to a confined liquid, the change in pressure is transmitted equally to all parts of the fluid. Draw a bottle of water with arrows to illustrate the regular exerted pressure. Then draw a water bottle that you squeeze. What happens to the pressure? What happens if you open the top? How does Pascal’s Principle explain what happens if you squeeze a water bottle?

15. A force applied to one section of an enclosed liquid at rest will be transferred to the entire liquid with the same amount of force.

16. Hydraulic Systems A force applied to one piston increases the fluid pressure throughout the fluid. If the second piston has a larger surface area, the force is multiplied! Pressure = Force/Area Force/Area = Pressure = Larger Force/Larger Area