The document discusses the four main forces that affect aircraft in flight: lift, which acts upward; drag, which acts backward; weight, which acts downward; and thrust, which acts forward. It provides definitions and examples of each force, explaining that for an aircraft to take off and stay aloft, lift must be greater than weight and thrust must be greater than drag, while the opposite is true for landing.

1. FORCES OF FLIGHT
1) Lift - upward
2) Drag - backward
3) Weight - downward
4) Thrust - forward
http://www.grc.nasa.gov/WWW/K-12/UEET/StudentSite/dynamicsofflight.html#forces

2. LIFT
• Lift is the force that acts upward against gravity and makes it
possible for heavier-than-air aircraft to rise in the air
• When you fly a kite, the wind compresses air against the kite,
pushing it upward and keeping it aloft.

3. DRAG
• Drag is air resistance
• This resistance opposes an aircrafts motion through the air
• Drag is useful when you want to slow an object down such as
an airplane or space shuttle
• Space shuttles use parachutes to create drag
• You don't notice the air's drag when you walk or run. But you
feel the force of drag when you try to move through water. Fish
and dolphins must have a streamlined shape to reduce their
drag.
http://www.fi.edu/flights/own2/drag.html

4. WEIGHT
• Weight is the force generated by the gravitational attraction of
the earth on the airplane.
• When an airplane takes off the weight of the airplane is
calculated very carefully or the plane may not be able to take
off.
http://www.grc.nasa.gov/WWW/K-12/airplane/weight1.html

5. THRUST
•Thrust is the force which moves an aircraft through the air.
•Thrust is used to overcome the drag of an airplane, and to
overcome the weight of a rocket.
•Thrust is generated by the engines of the aircraft through some
kind of propulsion system.
http://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.html

6. Relationships between the forces of lift, weight,
thrust, and drag that are required for flight
• lift must be greater than weight for a plane to take off
• thrust must be greater than drag for a plane to take off
• lift must be less than weight for a plane to land
• thrust must be less than drag for a plane to land