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Air, Air Pressure and Flight

Air, Air Pressure and Flight. ESCI 215 Chapter 11. Background. 1903 Orville and Wilbur Wright flew the first airplane They used a curved shaped propeller called an airfoil. Properties of Air. Negative Properties of Air: N o colour No smell No taste Cannot be seen

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Air, Air Pressure and Flight

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  1. Air, Air Pressure and Flight ESCI 215 Chapter 11

  2. Background • 1903 Orville and Wilbur Wright flew the first airplane • They used a curved shaped propeller called an airfoil

  3. Properties of Air • Negative Properties of Air: • No colour • No smell • No taste • Cannot be seen • Positive Properties of Air: • Is a substance • Occupies (takes up) space • Events 11-A, 11-B, 11-C, 11-D illustrate these properties of air

  4. Air Exerts Pressure • Air pressure at sea level = 1 kg/cm2 • Why does air not crush what it touches? • Air pressure pushing on objects = pressure with objects pushing out • Air pressure with elevation • Popping in ears during take-off and landing in planes • Events 11-G, 11-H, 11-I, 11-J show that air exerts pressure • Events 11-K and 11-L show the effects of air pressure and gravity • Event 11-M shows that air pressure occurs in all directions

  5. Air Expands and Contracts • Air expands when heated and contracts when cooled • The greater the heat, the greater the expansion • Events 11-O, 11-P and 11-Q show this principle • Event 11-R shows that air can be compressed

  6. Forces of Flight • 4 forces act on airplanes in flight: • Lift – upward force that offsets gravity • Gravity – downward force • Thrust – force that moves plane ahead • Drag – force that holds plane back • Common misconception: planes lift as air hits the underside of wings and pushes it up • Event 11-S disproves this misconception • Blowing air above a piece of paper can lift the paper • Illustrates how planes get lift

  7. How do Planes get Lift? • Top surface of wing is curved and lower surface is flat • Air over the wing has to travel farther than air under wing, making it travel faster • Forms a high speed column of air above the wing that has low internal pressure • Slower moving air under the wing has higher pressure • Wing is pushed up into the low pressure air column • Most of the lift in planes comes from the high-speed column of air that forms above the wing

  8. Bernoulli’s Principle • Bernoulli’s principle shows the relationship between the flowing air column and the change in pressure • Events 11-T, 11-U, 11-V, 11-W show the effects of low pressure of moving columns of air and the high air pressure of static air

  9. Streamlining for Speed • Increased speed = increased drag • Shape affects drag • Events 11-X and 11-Y show how shape affects drag • Blunt (not sharp) shapes cause drag in 2 ways: • Resistance to air as the object moves • Suction and turbulence of the air behind it

  10. How Airplanes are Controlled • Planes need controls for: • Elevators control up and down motions • Angled up – tail pushes down and plane climbs • Angled down – tail pushes up and plane points down • Rudder controls left and right motions; on the vertical tail section • Angled left, air pushes tail to the right and nose to the left • Angled right, air pushes tail to the left and nose to the right • Ailerons control the clockwise and counterclockwise roll; one on each wing • Angle 1 aileron up and the other down to tilt or roll a direction • Flaps control the lift when flying slowly during takeoff and landing; one on each wing • Angled down, increases the lift • Event 11-Z tests all the motions of the plane

  11. Supersonic Flight • Some aircrafts travel at or above the speed of sound • Military aircrafts travel 2 or 3 times the speed of sound • When traveling at the speed of sound, the principle of lift changes • Air going over wing travels faster than the plane due to curved wing • Air column reaches the speed of sound before the plane • Air piles up and forms a higher pressure column that pushes down on the wing • Wings of supersonic planes are not curved and are thin to reduce resistance • Pressure builds as speed increases and pressure reaches the ground producing a sonic boom

  12. Misconception – sonic boom occurs only when the plane “breaks” the sound barrier • Sonic boom occurs continuously as long as the plane is flying at or above the speed of sound • We only hear a single boom because we only hear a small portion of this continuous sound as it keeps travelling past us • Events 11-AA and 11-BB have students investigate this misconception

  13. Assessment and Instruction • Task: • Enlarge a diagram from a discrepant event not used in class • Remove the labels and direction arrows • Copy onto transparencies • Give a copy to each group of 3 or 4 • Students discuss how air pressure works in the event • Students write an explanation and draw arrows to show understanding of the air pressure • Randomly select 1 student from each group to show their group’s ideas to the class • Class discusses which group(s) explanation are effective and accurate

  14. Websites • www.nasm.si.edu • www.lerc.nasa.gov/WWW/k-12/TRC/rockets • www.geocities.com/CapeCaraveral/1817/resource.html • www.irving.org/rocketry • www.howstuffworks.com/boomerang.htm • www.windows.ucar.edu

  15. Discussion • Where does this topic fit into the Science curriculum? • Which grades and strands? • Which curriculum objectives relate to the discrepant events?

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