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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.
The main idea of this passage is______.
选项 A、different weight systems in different places
B、freedom from traditional ideas
C、traveling from the earth to the moon
D、the effect of gravitation on weight
答案D
解析 本篇文章通篇讲的是重量是由引力产生的，并进一步阐述了物体问引力的变化、物体本身的重量，以及物体间的距离这三者之间的关系，主要讲的还是引力对重量的作用。
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本试题收录于： 职称英语理工类C级题库职称英语分类
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