题目内容
Because we can feel that things are very heavy, we think of “weight” as being a fixed quality, 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 gravity(引力)for all other objects; this is called gravitational attraction(万有引力). But this power of attraction between two objects gets weaker as they are 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 make the distance three times far away, it gets nine times weaker (three times three). If you make it four times far away, it gets sixteen times weaker (four times four) and so on.
So this is one of the first things we need to remember: the weight of an object in space is not the same as its weight on the surface of the earth.
1.Which of the following is right?
A.A thing has the same weight everywhere in space.
B.“Weight” is a fixed quality in an object.
C.“Weight” is not a quality in an object.
D.A thing’s weight changes with its place in space.
2.There is between .
A. gravity; objects? B.power; all objects
C.gravity; the two objects only? D.power; two things
3.A 400 pound man-made satellite is sent to the place 2 000 miles out from the earth. Its weight is about .
A.200 pounds B.a half pounds
C.100 pounds D.300 pounds
4.If we make the distance between objects five times as far away, .
A. it gets twenty-five times weaker
B.their weight gets twenty-five times weaker
C.their gravity gets twenty-five times weaker
D.their gravity gets twenty-five times stronger
5.After reading this passage, we should remember that we know the usual weight of a thing .
A. because it is on the surface of the earth
B.because it is weighed
C.because it is in space
D.because it is not far away from the earth