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原来,他发现牛顿在书中画了一幅神奇的图画(如图所示).这幅图是牛顿说明人造地球卫星的草图。表示水平抛出的石头,速度越大,落地点越远.牛顿用引力公式算出当石头初速达到5英里/秒。(约7.9公里/秒)时.它就象天上的那轮明月似地永恒不坠,一圈又一圈地环绕地球运转了.这就是人造小月亮,也就是人造地球卫星.在地面附近,若卫星速度小于7.9公里/秒,将逐步坠落地面.
Originally, he found that Newton drew a magical picture in the book (as shown in the figure). This picture is a sketch of Newton’s description of an artificial earth satellite. The stones that are thrown horizontally, the higher the speed, the farther the location is. Newton uses gravitational formulas to calculate when the initial velocity of the stone reaches 5 mph. (about 7.9 km/s). It will never fall like the bright moon in the sky. It will circle around the earth. It is a man-made moon, that is, a man-made earth satellite. Near the ground, If the satellite speed is less than 7.9 km/s, it will gradually fall to the ground.