来自《耶鲁大学开放课程：基础物理 第3集 第3集》

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  Then I ask you, "What is two meters and what is three meters?"
  然后我问你 "两米有多长 三米有多长"
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  We have ways of doing that.
  我们可以量出来
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  I take the meter and put it next to the meter, that's two meters.
  我们给一米接上一米 那就是两米了
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  I cut it in half,
  把它切成两半
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  I'll use some protractors and dividers and compasses,
  我用量角器 两脚规 还有圆规
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  you can split the meter into any fraction you like.
  你想把一米分成任意份数
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  Likewise for mass,
  质量也是这样
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  we will take a chunk of some material
  我们找来一大块材料
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  and we will call it a kilogram.
  然后称它为 1 千克
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  I should give you some hint.
  我应该给你们一些提示
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  That kilogram, I don't expect you to deduce.
  那 1 千克 我没指望你们能推导出来
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  That is a matter of convention.
  那是约定俗成的