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. 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

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

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