There is another aspect of flying we must know about, that is flying speeds. There are, in fact, two kinds of speed, the ground speed, which is the speed relative to the air. These are two quite different things.
Let us go back to the kite for a moment, if, instill air, you run with a kite at five miles per hour, its ground speed will be five miles per hour because that is the actual speed at which you are pulling it over the ground. Now, suppose you are running at five miles against a light breeze of five miles per hour. The ground speed will still be the same but, because the air is passing the kite at ten miles per hour, the air speed of the kite will be ten miles per hour; that is, the speed at which you are running plus the speed of the air is passing the kite at five miles per hour, so its air speed is five miles per hour.
Ground speed decides how long an aero plane will take to fly from one place to another. Air speed provides the lifting force and the drug. Your kite will remain in the air in a good breeze even if you stand still, and you will still feel the drag on the string.
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