来自《耶鲁大学开放课程：基础物理 第3集 第3集》

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  take the derivative of this,
  对这个式子求一次导
• 
  
  get the velocity vector
  就能得到速度矢量
• 
  
  and you notice his magnitude is a constant
  你会发现其模长是常数
• 
  
  and the constant will be ωr.
  而这个常数正是 ωr
• 
  
  Whichever way you do it,
  不管用什么方法
• 
  
  you can then rewrite this as v square over r.
  加速度也可以写成 v^2 / r
• 
  
  This is called the centripetal acceleration.
  这就是向心加速度
• 
  
  This is the acceleration directed toward the center.
  加速度方向指向圆心
• 
  
  I told you these are very important results.
  这是一个很重要的结论
• 
  
  You've got to get this in your head.
  你们得牢牢记住
• 
  
  Whenever you see a particle moving in a circle,
  只要看到质点做圆周运动
• 
  
  even if it's at a constant speed,
  即使是匀速圆周运动