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Air Pressure and Wind

Air Pressure and Wind. The force exerted by air molecules as they collide with a surface The weight of the atmosphere as it pushes on Earth’s surface. What is air pressure?. Air has mass Gravity pulls these molecules towards Earth giving them weight

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Air Pressure and Wind

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  1. Air Pressure and Wind

  2. The force exerted by air molecules as they collide with a surface The weight of the atmosphere as it pushes on Earth’s surface What is air pressure?

  3. Air has mass Gravity pulls these molecules towards Earth giving them weight The weight of the molecules is air pressure kg What is air pressure?

  4. What is air pressure? • At sea level the weight of air pushing down is 14.7 pounds per square inch • The weight on the roof of a typical house is about 2.1 million kg (4.6 million lbs) Why don’t all of our houses collapse? Or Why aren’t we all squished? CHECK THIS OUT!!! Extreme Atmospheric Pressure

  5. Air pressure is exerted (pushes) in all directions An equal force pushing down is balanced by air pushing up What is air pressure?

  6. What Is Air Pressure? • The same thing as gravity • The weight of the atmosphere pushing downward • A form of pollutant

  7. Why Don’t We Get Crushed By The Pressure Of The Atmosphere? • The air is not that heavy • Air pressure is exerted in all directions, and we are in equilibrium • The water in our bodies prevents it

  8. Why Did The Oil Drum Collapse? • The water weakened it • The atmosphere suddenly got heavier • The cooling vapor took up less space than before and created a drop in pressure inside. The regular air pressure then crushed the drum.

  9. The barometer is the instrument used to measure air pressure 2 types of barometers Mercury Aneroid Mercury Barometer Measuring air pressure

  10. Measuring air pressure • As the weight of the air increases, the mercury rises

  11. Measuring air pressure • As the weight of the air decreases, the mercury lowers

  12. Measuring air pressure The Aneroid barometer • A capsule with most of the air removed changes size as the pressure outside of it increases or decreases • This moves the needle

  13. Measuring air pressure • Pressure will be measured in • Mm Hg • Inches of Hg • Milibars • Average Pressure at sea level • 1013.25 mb = 29.92 in. Hg

  14. Why does air pressure change? • 3 factors that affect pressure: • Elevation/Altitude (p414) • Temperature (p416) • Humidity (p416)

  15. Complete the graphic organizer by filling in the 3 factors that affect pressure. Then create branches explaining how they cause pressure to change.

  16. Changes in air pressure • Altitude (height above sea level) • As the altitude increases pressure decreases • As the altitude decreases pressure increases

  17. Changes in air pressure Altitude Drawing High Altitude / Low Pressure Low Altitude / High Pressure

  18. Changes in air pressure Humidity (the amount of water vapor in air) • Water molecules weigh less than O2 or N2 • Water vapor replaces these molecules in humid air • As humidity increases, pressure decreases • As humidity decreases, pressure increases HUMID AIR DRY AIR

  19. Humidity Drawing Changes in Air Pressure Low Humidity / High Pressure High Humidity / Low Pressure

  20. Changes in air pressure Temperature • In warm air the molecules are far apart. • In cool air the molecules are closer together • As air temperature increases, pressure decreases • As air temperature decreases, pressure increases

  21. Changes in air pressure Temperature Drawing High Temperature / Low Pressure Low Temperature / High Pressure

  22. Let’s Summarize

  23. Low Pressure Generally associated with stormy weather. The air is rising.

  24. High Pressure Generally associated with clear skies. Air is sinking.

  25. What makes the wind blow? • Air moves from HIGH PRESSURE to LOW PRESSURE • This movement of air is WIND

  26. What does a barometer measure? • Atmospheric pressure • The humidity of the air • Air quality • How much it has rained

  27. What affects air pressure? • Altitude • Humidity • Temperature • All of the above

  28. Why is water vapor less dense than air? • There is less of it • H2O has less mass than O2 or N2 • It is hotter, so it has less mass

  29. Low pressure is usually associated with… • Sunny skies • Deserts • Earthquakes • Stormy weather and rising air

  30. High pressure is usually associated with… • Rain • Tornadoes • Sunny, dry weather with sinking air • Pushy car salesmen

  31. Factors Affecting Wind Direction and Speed

  32. What makes the wind blow? • Island Example

  33. Factors Affecting Wind Direction • Coriolis Effect Coriolis-2.mp4 • Pressure Gradients (differences in pressure HIGH vs LOW) • Friction (resistance)

  34. The Coriolis Effect • An object moving over Earth’s surface will curve away from its intended path • This is due to Earth’s rotation • Faster at the equator • Slower at the poles

  35. Guidelines (p419): objects are deflected to the RIGHT in the Northern Hemisphere and the LEFT in the Southern Hemisphere The effect (curve) increases as the speed increases The effect DOES NOT depend on the objects direction The effect is greater at the poles and less at the equator Most noticeable of large distances (Not in TOILETS) Coriolis-1.mp4 The Coriolis Effect

  36. The Coriolis Effect • Let’s Draw!

  37. Pressure Gradients • Pressure gradient: • A difference in pressure from one place to another • Remember wind blows from HIGH to LOW • The stronger the gradient the faster the wind • The faster the wind the more curve from the Coriolis Effect

  38. Friction • Friction between the air and the ground slows wind. • The higher above the surface the faster the wind will blow • The higher above the surface the more curve due to Coriolis

  39. Friction • Little friction in the upper troposphere allows a jet stream to from moving air west to east. • The jet stream supplies energy to storms and directs the path of weather across the United States • Affects airplanes as they travel coast to coast

  40. Jet Stream

  41. Review Questions • What are the 3 factors that affect wind direction? • What are the 3 factors that affect air pressure? • How does a pressure gradient affect the speed of wind? Direction of wind? • Why does the Coriolis Effect cause wind to deflect? • Can you witness the Coriois Effect in your bathroom? • How does friction affect wind speed?

  42. What are the 3 factors that affect wind direction? • Altitude, Humidity, and Temperature • Altitude, Humidity, and Coriolis Effect • Coriolis, Pressure, Gradients, and Friction

  43. What are the 3 factors that affect air pressure? • Altitude, Humidity, and Temperature • Coriolis, Pressure, Gradients, and Frction • Sunlight, Convection, and Friction

  44. How does a pressure gradient affect the speed of wind? • The stronger the gradient, the weaker the wind • The stronger the gradient, the stronger the wind • It does not effect the speed

  45. Why does the Coriolis Effect cause wind to deflect? • The wind was already curving; the Coriolis Effect only effects airplanes • The spinning of the Earth causes the path to curve

  46. How does friction affect wind speed? • Objects or rough surfaces cause a drag on the wind • Friction makes the wind faster • Friction creates wind

  47. Global and Local Winds

  48. Global Winds • Global winds show the general direction the air is flowing throughout the globe. • Refer to your worksheet for these winds • The winds are named according to where the wind comes from or originates • Ex. What would the name of this wind be?

  49. Global Winds Climate Zones due to global winds: • Areas of low pressure are characterized by rising air, precipitation = Rainforest (0, 60) • Areas of high pressure are characterized by sinking air, dry air = Deserts (30, 90) ** Add these areas to your worksheet

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