Chapter 7 Section 3

Objectives: Describe the relationship between pressure

and fluid speed

Analyze the roles of lift, thrust, and wing size in flight

Describe drag, and explain how it affects lift

Explain Pascal’s principle

Fluid Speed & Pressure:Property of moving fluids- Bernoulli’s Principle

As the speed of a moving fluid increases, the fluid’s pressure decreases

Ex: try the two sheets of paper demoEx: table tennis ball in a stream of water

http://pilotsweb.com/principle/art/venturi01.jpg

Factors That Affect Flight:Bernoulli: fast moving air above the wing exerts

less pressure than slow moving air below the wing; the greater pressure below the wind exerts an upward force [Lift] – wing shape is the key!

Lift pushes the wings upward against the downward pull of gravity

http://www.hiflykites.co.za/kite-online-shop/x-zylo-flying-principles-3.gif

Thrust & Lift:Amount of lift is determined by the speed of

the air traveling around the wing

Speed is determined by thrust

Thrust: the forward force produced by a plan’e’s engine

http://www.yesmag.ca/focus/flight/bernoulli.gif

http://library.thinkquest.org/2819/graphics/forces.jpg

Wing Size, Speed, and LiftLift depends on wing size

Jet create a large amount of lift with small wings because it has a strong thrust

Glider has large wings to create lift, no engine, no thrust,

Bernoulli & Birds:Birds flap wings because they have no engines

Small birds flap at a fast rate, large birds flap slowly

Bernoulli & Baseball:

Throwing a screwball or curveball that is difficult to hit

http://library.thinkquest.org/C005776F/images/curveball.jpg

http://www.lokeshdhakar.com/images/2007/baseball_pitches/screwball.png

Drag & Motion in Fluids:

Drag: the force that opposes or restricts motion in a fluid

Ex: walking in a strong wind

Caused by an irregular flow of air “turbulence”

Turbulence & Lift:

Lift is reduced when turbulence causes drag

Planes have flaps to reduce turbulence

Flaps change the shape or area of the wing, reducing drag and increasing lift

http://virtualskies.arc.nasa.gov/aeronautics/tutorial/images/FlapsAilerons.gif

Pascal’s Principle:A fluid in equilibrium contained in a vessel exerts

a pressure of equal intensity in all directions

A change in pressure at any point in an enclosed fluid will be transmitted equally in all parts of that fluid

http://panda.unm.edu/Courses/Price/Phys160/F33-3.jpeg

Pascal’s Principle & Motion:

Hydraulic devices use Pascal’s principle to move of lift objects

Hydraulic devices can multiply forces (use liquids)

Ex: car brakes

Quick Quiz:

What forces act on an aircraft?

When an airplane is flying, does the air pressure above a wing compare with that below the wing?

How is thrust related to the speed of an airplane?