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: 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

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

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

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

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

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

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

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

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

Events 11-AA and 11-BB have students investigate this misconception 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

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

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

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