来自《耶鲁大学开放课程：基础物理 第7集 第7集》

• 
  
  you wait a week, it's there,
  一礼拜后它在这儿
• 
  
  and you wait another week it's there.
  再过一个礼拜后它到了这里
• 
  
  You join these two lines
  你把这两条线放在一起
• 
  
  and you call that the area swept out by the planet in the first week;
  你称这个为行星第一周扫过的面积
• 
  
  then, in the second week, the area swept out is that.
  然后 在第二周 扫过的面积是这一部分
• 
  
  So, it's the area intercepted by the two radial vectors
  这个区域是由两个径向矢量
• 
  
  and the arc along which you move.
  和你移动的弧截取的
• 
  
  And Kepler said the rate at which the area is swept out --
  开普勒说面积被扫过的速率
• 
  
  let dA/dt be a shorthand for
  用 dA/dt 来作为一个简写
• 
  
  how much area is covered in a certain time --
  描述在一定时间内被覆盖的面积
• 
  
  so you take area swept out, divide by Δt,
  这样你把扫过的面积除以 Δt
• 
  
  and he said that's a constant.
  他说这个值是常量