综合类相同项单选集试卷（综合类）_6.docVIP

试卷第 PAGE 1 页共 NUMPAGES 1 页 综合类相同项单选集试卷（综合类） 姓名:_____________ 年级:____________ 学号:______________ 题型 选择题 填空题 解答题 判断题 计算题 附加题 总分 得分 评卷人 得分 1、Weight on and off the Earth We are so used to our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted. Because we can feel that things are heavy, we think of “weight” as being a fixed quality in an object, but it is not really fixed at all. If you could take a one-pound packet of butter 4,000 miles out from the earth, it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space The reason is this: All objects have a natural attraction for all other objects; this is called gravitational attraction. But this power of attraction between two objects gets weaker as they get farther apart. When the butter was at the surface of the earth, it was 4,000 miles from the center. When we took the butter 4,000 miles out, it was 8,000 from the center, which is twice the distance. If you double the distance between two objects, their gravitational attraction decreases four times (two times two). If you treble the distance, it gets nine times weaker (three times three) and so on. So this is one of the first things we need to remember: that the weight of an object in space is not the same as its weight on the surface of the earth. What about the weight of our pound of butter on the surface of the moon At the distance the pull of the earth is about 4,000 times smaller than it is here on the surface, so we can forget all about the earth-pull on our butter. On the other hand, on the moon there will be an attraction between the butter and the moon, but the butter will weigh only about one-sixth as much as it does on the earth. This is because the moon is so much smaller than the earth. The amount of gravitational pull that a body produces depe