来自《耶鲁大学开放课程：基础物理 第11集 第11集》

• 
  
  If it's not moving, the force of gravity acts on it,
  如果它没有运动 重力作用于它
• 
  
  causes an acceleration toward the center.
  引起一个指向地心的加速度
• 
  
  That means what you and I think it means, falling toward the center.
  众所周知 这意味着它朝着地心下落
• 
  
  But if you take an apple with a huge velocity to begin with,
  如果你在开始给苹果一个很大的速度
• 
  
  add to it an acceleration toward the center,
  加上指向地心的加速度
• 
  
  or a tiny increment of velocity in this direction--
  或者在这个方向 加一点小的速度增量
• 
  
  we will just give it that velocity--
  它就有具有这样的速度
• 
  
  and that's the velocity it has when it has come here
  这个速度让它向这个方向运动
• 
  
  Same thing with the gyro.
  陀螺的情况相同
• 
  
  The gyro does get the same angular momentum ΔL that it would
  陀螺同样得到一个角动量 ΔL
• 
  
  whether or not it was rotating
  无论它是否旋转
• 
  
  But in one case, you add it to zero
  一种情况是 初始角动量是零