Forces and Flight

The four forces that act on an airplane in flight are thrust, drag, lift, and weight.  When the propellers of the airplane turn, they exert a force that pushes air backward.  He air exerts an equal force on the propellers, forcing them, and the airplane forward.  This forward force is thrust.  The air causes drag.  As the airplane moves forward, this force acts in backward direction.  The amount of lift is related to the shape of the wing and the forward velocity of the airplane.  The faster the airplane moves, the greater the lift force.  Weight is a downward force caused by gravity.  The faster the airplane moves, the greater the lift force.  Weight is a downward force caused by gravity.  The greater the mass of the airplane and its contents, the greater the downward force.

1.    Which of the forces described form a pair of action-reaction forces? 

2.    Which of Newton’s laws describes such a pair of forces?

3.    Which two forces must be balanced if the airplane is to fly at a constant forward velocity?

4.    Which of Newton’s laws describes such balanced forces?

5.    Which two forces must be balanced if the airplane is to fly at a constant altitude?

6.    To take off, an airplane must accelerate until its forward velocity gives it enough lift to get off the ground.  What are two ways in which the mass of the airplane affects takeoff?

7.    Flaps on the airplane wings can be moved to change the shape of the wings.  During landing, the flaps decrease lift and increase drag.  How do these changes help the airplane to land?

8.    As the airplane moves through the air, two factors cause drag.  What are they? 

9.    Why do they cause drag to be greater at low altitudes?