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Section 1: Pressure

Section 1: Pressure. What does pressure depend on? How do fluids exert pressure? How does fluid pressure change with elevation and depth?. Definition : The area of a surface is the number of square units that it covers. Area. Equation : Area = Length • Width.

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Section 1: Pressure

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  1. Section 1:Pressure • What does pressure depend on? • How do fluids exert pressure? • How does fluid pressure change with elevation and depth?

  2. Definition: The area of a surface is the number of square units that it covers. Area Equation: Area = Length • Width The area of the rectangle below is 2 cm X 3 cm, or 6 cm2.

  3. Math Solution Which has a greater area: a rectangle that is 4 cm X 20 cm or a square that is 10 cm X 10 cm? The square has the greater area. 4 cm X 20 cm = 80 cm2 10 cm X 10 cm = 100 cm2 Area

  4. What Is Pressure? • Definition: The force exerted on a surface divided by the total area over which the force is exerted.

  5. What Is Pressure? Equation: Pressure = Force Area Pascal (Pa) = 1 N/m2

  6. Fluid Pressure • All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid.

  7. Did you know you live at the bottom of 100 kilometers of fluid?

  8. Did you know you live at the bottom of 100 kilometers of fluid? • This fluid is called AIR! The mixture of gases in the Earth’s atmosphere press down on everything on Earth. Air exerts pressure because it has mass.

  9. Did you know you live at the bottom of 100 kilometers of fluid? • This fluid is called AIR! The mixture of gases in the Earth’s atmosphere press down on everything on Earth. Air exerts pressure because it has mass. • Each cubic meter of air around you has a mass of about 1kg

  10. Balanced Pressure • Hold out your hand.

  11. Balanced Pressure • Hold out your hand. • You are holding up air.

  12. Balanced Pressure • Hold out your hand. • You are holding up air. • At sea level, the atmospheric pressure is about 101,300 Pa. • The surface area of your hand is about 100cm2

  13. Balanced Pressure • Hold out your hand. • You are holding up air. • At sea level, the atmospheric pressure is about 101,300 Pa. • The surface area of your hand is about 100cm2 • So, that means the weight supported by the surface area of your hand is about 1000 newtons… about the same weight as a large washing machine!

  14. HOW is that possible? • Because in a stationary fluid, pressure at a given point is exerted equally in all directions. • It presses on your hand in every direction… and the pressures balance each other. • This is why the tremendous air pressure does not crush you.

  15. Variations in Fluid Pressure • As your elevation increases, atmospheric pressure decreases.

  16. Variations in Fluid Pressure • Water pressure increases as depth increases.

  17. Measuring pressure • You can measure atmospheric pressure with a barometer. • Weather forecasters use these to forecast weather. • High pressure= good weather/clear • Low pressure= storms

  18. Air Pressure Explained • http://ed.ted.com/on/mP7zynGM

  19. Questions • Since most of the weight of the atmosphere is above you, why aren’t you crushed by it? • Compare the change in atmospheric pressure with elevation to the change in water pressure with depth. • Why must an astronaut wear a pressurized suit in space? • Give 3 facts, formulas or definitions you learned. • Write a 2 sentence summary. • What is 1 question you still have?

  20. End of Section:Pressure

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