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全国热气球锦标赛
地方性遗产
您看过Flying
Purple Eater(会飞的紫色贪食者)？假如您在八月来到爱荷华州的印地安诺拉市，参加它的全国热气球锦标赛，您就有机会看到。Flying
Purple Eater是一个状似昆虫的热气球，它是这个为期三天的竞赛中，100多个参赛热气球的其中一个。
这个热气球锦标赛年年举办，1970年刚开始时，名叫美国气球操纵竞赛。您了解热气球的运作方式吗？气球是轻飞行器，也就是说，充气后，它们会比空气轻。一旦气球升空后，气团或风会带着它移动，而气球会随着它们的速度及方向在空中移动。
您还记得巫师是用什么方法抵达奥兹国的吗？他是坐热气球！热气球的驾驶员可以操控气球的高度(即热气球的飞行高低)，而且可以利用方向略有不同的气团，来改变热气球的飞行路线。热气球将通用空气拿来当作上升气体。驾驶员会加热热气球内部的空气，使其比外部的空气轻，促使热气球上升。当内部的空气冷却后，除非驾驶员再次加热，否则热气球就会变重，开始下降。
Have you ever seen a Flying Purple Eater? If you go to the National Balloon Classic in Indianola, Iowa, in August, you just might. The Flying Purple Eater is an insect-like hot-air balloon -- one of more than 100 -- that takes part in this three-day event.
Held each year, this hot-air balloon competition and race began in 1970 as the first U.S. National Championship in ballooning. Do you know how hot-air balloons work? Balloons are aerostats, which means that they are lighter than air when inflated. Once a balloon is in the air, it moves with an air mass or wind, which carries it along at the same speed and in the same direction as the air.
Do you remember how the Wizard landed in Oz? He was in a hot-air balloon. The pilot of the balloon has control of the altitude (how high or low the balloon flies) and can alter its course by finding an air mass going in a slightly different direction. Hot air balloons use ordinary air as the lifting gas. By heating the air inside the balloon, the pilot makes that air lighter than the outside air, and the balloon rises. As the internal air cools, the balloon becomes heavier and descends unless the pilot adds more heat.
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