来自《耶鲁大学开放课程：基础物理 第4集 第4集》

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  it'll make some angle here.
  这里有个角度
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  You want to know what it's going to do.
  你想知道物体接下来会怎样
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  All right, we know it's going to slide down the hill,
  好吧 我们知道它将会滑下斜坡
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  but we want to be more precise,
  但我们想知道得更确切些
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  and the whole purpose of Newton's Laws
  牛顿定律的全部目标就是
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  is to quantify things for which you already have an intuition.
  把我们有些直觉的东西给量化
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  So the only novel thing about the inclined plane is that
  斜面问题中唯一新奇的东西就是
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  for the first time we are going to pick our x and y axes
  我们会第一次用新的方式选取 x 轴和 y 轴
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  not along the usual directions,
  不是沿着以往习惯的方向
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  but along and perpendicular to the incline.
  而是沿着和垂直于斜面
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  That's going to be my x and that's going to be my y.
  这就是新的 x 轴和 y 轴
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  And I ask, what are the forces on this mass?
  我接下来要问 物体受到了哪些力的作用呢