英语听力文摘 English Digest 686 零重力是否真的存在？

Zero Gravity, Does It Exist?

This Moment of Science: Is there such a thing a zero gravity?

No Zero Gravity

Contrary to popular belief, there’s no such thing as zero gravity. Weightlessness and zero gravity are two different things. The earth’s gravity keeps the moon in orbit¹. And astronauts are generally much closer to earth than the moon is, which means that the earth’s pull on them has to be much stronger.

While we’re on Earth, we feel our weight because, as the Earth’s gravity pulls us into its center, the ground pushes back against our feet.

When astronauts orbit the earth, they’re still subject to gravity, but they’re moving sideways so quickly that even though they’re being pulled towards the earth, they’re not getting any closer to the center of the planet². In other words, they’re basically³ in a state of constant free fall, and that’s why they’re weightless.

Weaker Gravity

Keep in mind that gravity never disappears entirely⁴. It just gets weaker. And every object with mass, including you and me, has what’s known as gravitational attraction. Although you’re subject to all those forces, the Earth’s gravity masks their pull because the Earth is so large and so close.

So moving away won’t free you of the Earth’s gravity. All that would happen is that the Earth’s pull would be masked by the pull of some other object, like Mars⁵.

零重力是否真的存在？

这一科学时刻：有零重力吗？

无零重力

与普遍的看法相反，没有零重力。失重和零重力是两回事。地球的引力使月球保持在轨道上。宇航员通常比月球离地球更近，这意味着地球对他们的引力必须更大。

当我们在地球上时，我们会感觉到自己的重量，因为当地球的引力将我们拉到它的中心时，地面会向后推我们的脚。

当宇航员绕地球运行时，他们仍然受到重力的影响，但他们的侧向移动速度如此之快，以至于即使他们被拉向地球，他们也不会离地球中心越来越近。换句话说，它们基本上处于持续自由落体的状态，这就是它们失重的原因。

重力较弱

记住，重力永远不会完全消失。它只是变弱了。每一个有质量的物体，包括你和我，都有所谓的引力。尽管你受到所有这些力的影响，但地球的引力掩盖了它们的引力，因为地球如此之大，如此之近。

所以离开并不能让你摆脱地球的引力。所发生的一切就是地球的引力会被其他物体的引力所掩盖，比如火星。

1 orbit   

n.轨道；vt.使沿轨道运行；使进入轨道运行；vi.沿轨道运行，环行

参考例句：

• The space rocket was launched and went into orbit.宇宙火箭发射后进入轨道。
• We can draw the earth's orbit round the sun.我们可以画出地球绕太阳运行的轨迹。

2 planet   

n.行星

参考例句：

• Neptune is the furthest planet from the sun. 海王星是离太阳最远的行星。
• Rubbish, however, is only part of the problem of polluting our planet. 然而, 垃圾只是我们这个星球的污染问题的一个方面。

3 basically   

adv.基本上，从根本上说

参考例句：

• His heart is basically sound.他的心脏基本上健康。
• Basically I agree with your plan.我基本上同意你的计划。

4 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

5 Mars   

n.火星，战争

参考例句：

• As of now we don't know much about Mars.目前我们对火星还知之甚少。
• He contended that there must be life on Mars.他坚信火星上面一定有生物。