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该怎样思考重力

How to Think About Gravity - Jon Bergmann

什么是重力呢?
So what is gravity?
我觉得大多数人认为重力是
I bet most of you think it’s:
让上升的物体
‘What goes up,
下降的力!这个观点对吗?
must come down!’ Is that right?
嗯,不完全对。
Well, sorta, but not really.
从技术上讲,万有引力公式是一个等式
Technically, the law of gravity is an equation.
它是:F=GxM1xME/R^2,
It is: F = G x M1 x M2 / R^2,
其中,G是万有引力常数
where G is the universal gravitational constant,
M1和M2是两个物体的重量
M1 and M2 are the masses of the two objects,
R是它们之间距离的平方
and R is the distance between them squared.
这很容易,对吧?
That was easy, right?
也许并不容易。那么这个公式到底意味着什么呢?
Probably not. What does this actually mean?
它意味着任何物体都可以吸引其他的任何物体
Well it means that – well, everything is attracted to everything else.
简单来说,如果你有两个物体,任意两个物体
What I mean by that is if you have two objects, any two objects,
它们会相互吸引。那么,
they are attracted to each other. OK.
让我们试着理解这个定理
Let’s try and wrap our minds around this.
如果你试着将一块石头扔下悬崖,会发生什么呢?
What happens when you drop a rock off a cliff?
它会掉到地上。对吧?
It falls to the earth. Right?
那么,还有什么别的事情发生吗?
Well, yes, but something else happens.
你看,万有引力定律说两个物体
You see, the law of gravity says that both objects,
岩石和地球,相互吸引
the rock and the earth, are attracted to each other.
这意味着岩石落向地球
This means that the rock falls towards the earth,
并且地球落向岩石
and the earth falls towards the rock.
稍等,你的意思是地球下落然后遇见岩石吗?
Wait a second – you mean to tell me that if – the earth falls up to meet the rock?
是的,这就是我想说的
Yes, that’s exactly what I’m saying.
你没有看到地球落向岩石这一现象的原因是
And the reason you don’t see the earth fall up to meet the rock
物体相互吸引是与他们各自的质量成比例的
is because the objects move towards each other proportionate to their respective masses.
地球的质量比石块大的多
The earth is much much much more massive than the rock,
所以它移动了很小的距离
so it moves a very very small distance,
石块相对来说小的多,所以它移动的距离
and the rock is much less massive, so it moves farther
相对于地球来说要远
with respect to the earth.
理解重力的一个好方法是把两个穿着飞行服的志愿者
Maybe a better way to understand gravity is to take two teenagers
放在距离很远的星球上
in spacesuits, and place them far out in space – away from all the planets and the stars.
他们就会相互吸引
It turns out they will be attracted to each other.
我的意思可不是心灵吸引
I’m not talking about that kind of attraction.
看,他们有质量,也正是因为他们有质量
See, they have mass, and since they have mass,
他们会移向对方
they will move towards each other.
他们相互吸引
They are attracted to each other.
也许再来一个例子会更容易理解,你玩过磁铁吗?
Maybe one more thing might help. Have you ever played with two magnets?
你一定知道,磁铁都有北极和南极
You know, the magnets with the north and the south poles?
当你拿着两个磁铁并把它们相互靠近的时候
When you take the magnets and put them closer to each other,
它们移到一起了,然后它们就互相吸住了
they move together. They are attracted to each other.
它们距离越近,吸引力越大
And the closer they are, the stronger the attraction.
想象物体的质量就像磁铁的吸力一样
Think of the mass of the object like the strength of a magnet
物体间的距离就像磁铁间的距离
and the distance between the objects like the distance between the two magnets.
现在你要明白,我的意思不是说重力就是磁力
Now understand, I’m not saying that gravity and magnetism are the same,
只是它们的表现形式相同
they just behave in a similar way.
让我们再来思考另一件事,宇航员
Let’s think of one other thing – astronauts.
你知道,宇航员在月球上的重力
You know, astronauts, they weigh less on the moon
比在地球上小的多,这是为什么?
than on the earth. Why is that?
好的,月球的质量比地球小的多
Well you see, the moon is less massive than the earth.
所以它对宇航员有很小的拉力
Therefore it has a smaller gravitational pull on the astronaut.
就像月球是一块小磁铁一样
It’s like the moon is a weaker magnet.
他们不会像在地球上一样吸引
They aren’t as attracted to each other.
距离也扮演一个重要角色,回到磁铁这块
Distance also plays a role. Think back to playing with a magnet.
对于两块磁铁来说
The pull of the magnets towards each other
距离越近,拉力越强,重力亦是如此
are stronger when they are closer together. The same is true of gravity.
比如 太阳是地球周围质量最大的星球
For example, the sun is the most massive object near the earth.
它是我们太阳系的最大的引力
It dictates most of the gravitational forces in our solar system.
它的质量特别大,但是它距离我们很远
It is very very massive. But it is relatively far away,
即使太阳是最强的磁铁,但是老实说
so even though the sun is a much stronger magnet, so to speak,
距离太远了
it is a long ways away.
所以这个引力也不是很大
Therefore the attraction isn’t as strong.
所以我们返过头来看引力定律
So let’s look back at that law of gravity.
公式:F=G×M1×M2╱R²
The equation: F = G x M1 x M2 / R ^2.
你会看到引力是等于一个数字的
You see the force of gravity is equal to a number.
这就是万有引力常数G
That’s that universal gravitational constant G
乘以物体1再乘以物体2的质量
times the mass of object one, times the mass of object two.
想象物体1是太阳的质量
Think of M1 being the mass of the sun
物体2是地球的质量
and M2 being the mass of the earth.
然后除以他们之间距离的平方
And then we divide by the distance between them squared.
这就是太阳和地球之间引力的大小
This determines the force of attraction between the sun and earth.
你可以同样的作用于你的质量
You could just as easily plug in your mass
和地球的质量还有你和地球中心的距离
and the earth’s mass and the distance between you and the center of the earth,
就能计算出地球对你的引力有多大
and find out how much you are attracted to the earth,
和你对地球的引力
and the earth attracted to you.
那么,重力是什么?
So, what’s gravity?
任何事物之间都相互吸引
Everything is attracted to everything else.
是任何东西。嗯,最后还有一件事
Everything. Oh, one last thing,
这会让你惊奇。。。什么创造了重力
just to make you wonder. What causes gravity?
为什么两个有质量的物体会相互吸引?
Why are two objects with mass attracted to each other?
嗯,答案就是~
Well, the answer is –
我不知道
We don’t know.
重力的产生原因目前仍然是一个困扰科学家的难题
The cause of gravity remains a mystery to scientists.
我们真的不知道什么产生重力
We don’t really know conclusively what causes gravity.
它是科学界一大难题
It is one of the great mysteries of science.

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