来自《耶鲁大学开放课程：基础物理 第3集 第3集》

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  You take a material like silver
  你拿某种材料 比如银
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  and put it in a glass case and that's the definition of a meter.
  把它放进玻璃柜里 那是一米的定义
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  It's not right or wrong.
  这没有对或错
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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
• 
  
  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