How to think about gravity - Jon Bergmann

Transcriber: Ido Dekkers Reviewer: Ariana Bleau Lugo

翻译人员: Minji Seo 校对人员: Yolanda Zhang

So what is gravity?

万有引力是什么？

我想你们大多会想起：

I bet most of you think it's:

“向上移动的东西，

"What goes up,

must come down!" Is that right?

一定会跌下来！” 对吗？

Well, sorta, but not really.

嗯，差不多吧，但不完全如此。

Technically, the law of gravity is an equation.

从学术的角度来说， 万有引力是一条公式。

Ｆ等于Ｇ乘Ｍ１乘Ｍ２除以Ｒ的平方，

It is: F = G x M1 x M2 / R^2,

where G is the universal gravitational constant,

而Ｇ是万有引力常数，

Ｍ１和Ｍ２是两个物体的质量，

M1 and M2 are the masses of the two objects,

and R is the distance between them squared.

Ｒ是它俩之间的距离，被平方了。

That was easy, right?

看起来很容易，对吗？

Probably not. What does this actually mean?

恐怕不是。 这个公式到底是什么意思呢？

Well it means that - well, everything is attracted to everything else.

它的意思是： 任何物体彼此间都会互相吸引。

What I mean by that is if you have two objects, any two objects,

我是说，如果你有两个物体， 随便两个东西，

they are attracted to each other. OK.

它们都会互相吸引，就这样。

Let's try and wrap our minds around this.

我们来想想看。

What happens when you drop a rock off a cliff?

你在悬崖边扔下一块石头， 会出现什么情况？

It falls to the earth. Right?

石头会掉在地上，对吗？

Well, yes, but something else happens.

没错，但还有其他事情发生。

You see, the law of gravity says that both objects,

很明显，万有引力定律说两个物体，

the rock and the earth, are attracted to each other.

也就是石头和地球，会互相吸引。

This means that the rock falls towards the earth,

意思是石头会落向地球，

and the earth falls towards the rock.

而地球也会“落”向石头。

Wait a second - you mean to tell me that if - the earth falls up to meet the rock?

等一等——你意思是—— 地球会迎着石头向上“落”吗？

Yes, that's exactly what I'm saying.

是的，我就是这个意思。

And the reason you don't see the earth fall up to meet the rock

你看不到地球迎着石头往上“落”的原因，

is because the objects move towards each other proportionate to their respective masses.

是因为两个物体会按 它们质量的比例向对方移动。

The earth is much much much more massive than the rock,

地球的质量比石头大得多，

so it moves a very very small distance,

所以它只移动了一个非常小的距离。

and the rock is much less massive, so it moves farther

而石头的质量小的多， 因此它相对于地球而言

with respect to the earth.

移动得远一点。

Maybe a better way to understand gravity is to take two teenagers

可能更容易明白万有引力的方法， 是叫两个年轻人，

in spacesuits, and place them far out in space - away from all the planets and the stars.

穿上宇航服，把他们放在外层空间—— 远离所有行星和恒星。

It turns out they will be attracted to each other.

我们会发现他俩会互相吸引。

I'm not talking about that kind of attraction.

我说的不是这种（感情上的）吸引力。

See, they have mass, and since they have mass,

我是说，他们有质量， 而正因为如此，

they will move towards each other.

他们会移向对方。

They are attracted to each other.

他们会被对方吸引。

Maybe one more thing might help. Have you ever played with two magnets?

或许另一个例子更容易理解。 你试过同时玩两块磁铁吗？

You know, the magnets with the north and the south poles?

就是有南极和北极的磁铁。

When you take the magnets and put them closer to each other,

当你让两块磁铁彼此靠近，

they move together. They are attracted to each other.

它们会对接起来，会互相吸引。

And the closer they are, the stronger the attraction.

它们的距离越近，吸引力越大。

Think of the mass of the object like the strength of a magnet

试着把物体的质量想象为磁铁的强度，

and the distance between the objects like the distance between the two magnets.

而物体间的距离就好比 两块磁铁之间的距离。

Now understand, I'm not saying that gravity and magnetism are the same,

不要理解错了，我不是说万有引力和 磁力是一样的东西。

they just behave in a similar way.

只不过它们有类似的行为。

Let's think of one other thing - astronauts.

让我们想想另一样东西——航天员。

You know, astronauts, they weigh less on the moon

航天员在月球上的体重

than on the earth. Why is that?

比地球上的轻。为什么呢？

Well you see, the moon is less massive than the earth.

我们知道，月球的质量比地球的少得多。

Therefore it has a smaller gravitational pull on the astronaut.

因此它对航天员的引力就比较小。

It's like the moon is a weaker magnet.

就好像月球是一块较弱的磁铁。

They aren't as attracted to each other.

它们之间的吸引力没那么大。

Distance also plays a role. Think back to playing with a magnet.

距离也很重要。 回想一下玩磁铁的时候。

The pull of the magnets towards each other

磁铁间的吸引力

are stronger when they are closer together. The same is true of gravity.

在它们彼此接近的时候比较大。 同样的情况也适用于万有引力。

For example, the sun is the most massive object near the earth.

例如，太阳是地球附近 质量最大的物体。

It dictates most of the gravitational forces in our solar system.

它操控了我们太阳系内的 大部份万有引力。

It is very very massive. But it is relatively far away,

它的质量非常庞大。 但由于它相对地球较远，

so even though the sun is a much stronger magnet, so to speak,

所以即便说太阳是一块强得多的磁铁，

it is a long ways away.

但它离我们太远了，

Therefore the attraction isn't as strong.

因此它的吸引力并不那么强。

So let's look back at that law of gravity.

再复习一下万有引力定律。

The equation: F = G x M1 x M2 / R ^2.

公式是：Ｆ等于Ｇ乘Ｍ１，Ｍ２， 除以Ｒ的平方。

You see the force of gravity is equal to a number.

可以看到万有引力对应一个数值。

That's that universal gravitational constant G

那就是万有引力常数Ｇ，

times the mass of object one, times the mass of object two.

乘第一个物体的质量， 再乘第二个物体的质量。

Think of M1 being the mass of the sun

假设Ｍ１是太阳的质量，

and M2 being the mass of the earth.

而Ｍ２是地球的质量。

And then we divide by the distance between them squared.

然后我们除以它们之间距离的平方。

This determines the force of attraction between the sun and earth.

这样就能计算出太阳和 地球之间的万有引力。

You could just as easily plug in your mass

你也可以代入你自己的质量

and the earth's mass and the distance between you and the center of the earth,

和地球的质量， 以及你和地心之间的距离，

and find out how much you are attracted to the earth,

从而得出你受到来自地球的引力，

and the earth attracted to you.

和地球被你吸引的力。

So, what's gravity?

那么万有引力究竟是什么？

Everything is attracted to everything else.

任何东西之间都会被互相吸引。

Everything. Oh, one last thing,

任何东西。噢，还有一件事，

just to make you wonder. What causes gravity?

你可能会很好奇。 万有引力是怎么形成的？

Why are two objects with mass attracted to each other?

为什么两个有质量的物体 会彼此吸引？

Well, the answer is -

答案是——

We don't know.

我们不知道。

The cause of gravity remains a mystery to scientists.

万有引力的成因 对科学家来说仍是个谜。

We don't really know conclusively what causes gravity.

关于万有引力的成因， 我们始终没有得出一个确凿的结论。

It is one of the great mysteries of science.

这是科学界最大的未解之谜之一。