英语听力文摘686 零重力是否真的存在？
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 orbit. 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 planet. In other words, they’re basically in a state of constant free fall, and that’s why they’re weightless.
Weaker Gravity
Keep in mind that gravity never disappears entirely. 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 Mars.
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