You cannot have a spring pulled only at one side, because then it will then accelerate with infinite acceleration in that direction.

你不可能对弹簧只施加一边的拉力,因为那样的话弹簧就会以无穷大的加速度加速,就在这个方向上

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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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So springs are always pushed or pulled on either side with the same force.

所以弹簧两边永远都是受到,相同的压力或拉力

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Then, you may have forces to the right, forces to the left pushing, pulling.

然后你就有向右的力,和向左的力,推力和拉力都有

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If your plan is to accelerate a 3 kg mass with an acceleration of 2 meters per second, you better have a rope that can furnish that force and it can take the tension of 6 Newtons.

如果你想用 2 米每秒平方的加速度,去拉一个 3 千克的物体,那么你就需要一根能提供拉力的绳子,并且它能够承受 6 牛的张力

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the ropes will be pulling the block with T in the other direction, then I got 10 Newtons here.

绳子也会对另一物体施加方向相反的拉力 T,于是我知道这里是 10 牛顿

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kg is being pulled by the rope on the right with a force that I'm going to call T, which stands for tension.

千克的物体受到绳子向右的一个拉力,我称它为 T,也就是拉力的意思

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We'll give it a name, but by linking that T to that T, we can also figure out the same T must be exerted on this one by Newton's third law, because if this block is the only one that could be pulling this rope with T.

我们先给它命个名,把这个 T 和那个 T 联系起来,利用牛顿第三定律,我们可以知道这个 T 也一定作用在这个物体上,因为如果这个物体是唯一,受到绳子拉力 T 的物体

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