来自《耶鲁大学开放课程：基础物理 第16集 第16集》

• 
  
  And it's very happy to be where it is.
  它随意摆动
• 
  
  Now, I come and give it a little push.
  我过来轻轻推它一下
• 
  
  It'll start oscillating.
  它开始摆动
• 
  
  It'll look like that, and some time later it'll look like that,
  它一会摆成这样 一会又摆成这样
• 
  
  it's going back and forth.
  来回地摆动
• 
  
  Your job is to find the ω for that hoop.
  你们的任务就是找出这个摆的 ω
• 
  
  So, you move it a little bit, and you find the restoring torque.
  让它摆动一点 找出回复力矩
• 
  
  And you're done.
  这样就搞定了
• 
  
  But you've got to do two things right to get the right answer.
  但要注意两个因素
• 
  
  You've got to find the moment of inertia for circular loop
  你要找出圆圈的转动惯量
• 
  
  not around the center,
  不是绕圆心
• 
  
  but around the point and the circumference.
  而是圆上的一点