来自《耶鲁大学开放课程：基础物理 第2集 第2集》

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  but it is worth going over some properties
  但复习一下相关的性质是很有必要的
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  and some may be new and some may be old.
  有些可能是新知识 有些是已经学过的
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  For the simplest context in which one can motivate a vector
  对于最简单的情况 我们能用矢量
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  and also motivate the rules for dealing with vectors,
  以及相关的规则来处理的
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  is when you look at real space, the coordinates x and y.
  是实空间 x-y 坐标系
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  And let's imagine that I went on a camping trip.
  假设我参加了一次野营
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  On the first day, here is where I was.
  第一天 我在这里
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  Then, I tell you I went for 5 km on the second day
  然后我第二天行进了5公里
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  and another 5 km on the third day.
  第三天又走了5公里
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  Then I ask you, "Where am I?
  然后我要问 "我在哪儿
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  How far am I from camp?"
  我离营地有多远"
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  You realize that you cannot answer that.
  你们会发现无法回答这个问题