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So, a massless body cannot have a net force on it, because the acceleration of the rope cannot be infinite.
所以没有质量的物体不会受到力,因为绳子的加速度不可能是无穷大
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Does that forces us to say, "Ah, so it's not ?" the same rope at the end as the beginning."
那我们是不是就必须说,“啊，这不是一开始那根绳子了“
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So, massless bodies will always have, like a massless rope, equal and opposite forces on the two ends.
所以无质量的物体,比如这个绳子,两边所受的力永远都相等
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The rickety bridge is one that's kind of a rope bridge.
摆桥是索桥的一种。
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Suppose I had a rope, that stretched from that into the room, all the way across-- to this end of the room.
假设我有一根绳子，从屋子的这一端，一直伸展到-,屋子的这一端。
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Either a rope is pulling, a rope is pushing it, you are pushing it, you are pulling it.
无论绳子是在拉你还是推你,无论你是在推物体还是拉物体
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This is very important, because when you buy a rope, they will tell you how much tension it can take before it'll snap.
这非常重要,因为你去买绳子,他们会告诉你,绳子能承受的最大拉力是多少
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What makes up a rope? Of course you know, ropes are basically bundles of fibers, very same fibers that have been woven together in a certain way.
绳子是由什么构成的？，你肯定知道，是由一束束纤维构成，是由一样的纤维按某种方式编织,在一起构成。
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you're looking for that equal and opposite forces acting at two ends of the rope.
你就得求出作用在绳子两端的,大小相等方向相反的力
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Whenever you're asked on a problem, "What's the tension on the rope?"
不管什么题目问你,"绳子的张力是多少"
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In all these examples, this rope is assumed to be massless.
在所有这样的题目里都假设绳子没有质量
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I got 3 kg and I have a rope.
有一个 3 千克的物体和一根绳子
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Very same rope--at that end, at this end.
同样的一根绳子，从那边到这边。
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So, tension on the rope is 6 Newtons.
所以绳子的张力是 6 牛
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That is called the tension on the rope.
那就是绳子的张力
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One rope here, one rope there.
一根在这里，一根在那里。
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