Why Is Gravity in Space Not the Same as Earth?

Every object in the universe pulls on every other object. This is called gravitation, or gravity. But the strength of that pull-- of gravity --depends on two things.

First, it depends on how much matter a body contains. A body (object) that has a lot of matter has a lot of gravitation. A body that has very little matter has very little gravitation. For example, the earth has more matter than the moon, so the earth’s pull or gravitation is stronger than the moon’s.

Secondly, the strength of gravitation depends on the distance between the bodies. It is strong between bodies close together. It is weak between bodies far apart.

Now let’s take a human being on earth. The earth has more matter than the human being, so its gravitation pulls him to the earth. But the earth behaves as if all its matter were at its center.The strength of gravity at any place, therefore, depends on the distance from the earth’s center.

The strength of gravity at the seashore is greater than at the top of a mountain. Now, suppose a human being goes some distance up into the air, away from the earth. The pull of the earth’s gravity will be even weaker.

When people go out into space, they are away from the earth’s gravitational field. There is no pull. They are in a condition of weightlessness. And this is why, in rockets and space capsules, weightless astronauts and objects float about in the air.



为什么引力在太空和在地球上一样?

宇宙中的每一个物体都将另一物体拽向自身。这叫引力。但那个拉力(引力)的强度取决于两个因素。

首先，它取决于一个天体所含物质的多少。一个天体（物体）所含的物质多，它的引力就大。一个天体所含的物质很少，它的引力也很小。比如，地球比月球含的物质多，所以地球的拉力或引力就比月球大。

其次，引力的强度还取决于天体之间的距离。天体之间靠得越近引力就越强，相反，天体之间隔得越远引力就越弱。

现在以地球上的一个人为例。地球比此人所含的物质多，所以它的引力把他牢牢地吸住。但地球的行为方式好像是，它所有的物质都集中在它的中心。因此，任何方位引力的强弱都取决于它同地心之间的距离。

海边的引力就比山顶的引力要大。现在，假设一个人离开地球，升到空中一段距离。地球对这个人的引力就会更弱些。

当人们进入太空，他们就离开了地球的引力场，那就没有引力了，他们就处于失重状态。这就是为什么在火箭和宇宙飞船里，失重的宇航员和物体会在空中漂浮。

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