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  3. 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 mi

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 mi

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问题                     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 miles from the center, which is twice the distance. If you double the distance between two objects, their gravitational attraction decreases 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 depends on the amount of material in it. A packet of butter has a gravitational pull of its own; but this is very small in relation to the pull of something as large as the moon, or the earth, or the sun.
We find it hard to break free from ideas connected with living on the earth because______.
选项 A、it demands too great an effort for us to do so
B、we are too familiar with the way things are to question the ideas
C、we have proved that those ideas are correct
D、we are so sure of ourselves that we never doubt anything on the earth
答案B
解析 第一段第一句表明，我们之所以不能打破固有思维，是因为我们已经习惯了地球上的生活，也就是说，我们正是因为太过熟悉地球上的事物，才没有去质疑这些固有思维。
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