Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 5.The airplane flying west to east within jet stream will （ ） ．