来自《耶鲁大学开放课程：基础物理 第4集 第4集》

• 
  
  and you're turning left,
  想要左转
• 
  
  and the road looks like this,
  路是这样的
• 
  
  going away from me.
  远离我的方向
• 
  
  Now, I don't have to draw this thing.
  我不需要画得这么具体
• 
  
  This road is a track,
  这条路就是跑道
• 
  
  a racetrack going around and round like this.
  一个像这样的圆形跑道
• 
  
  And I gave it some angle θ.
  令它的角度为 θ
• 
  
  This road has no friction
  这条路上没有摩擦
• 
  
  so it can only exert a force that way.
  所以只在这个方向存在力
• 
  
  But let me resolve that force into two parts,
  让我们把这个力分解为两部分
• 
  
  one like this and one like this.
  一个是这样的 另一个是这样的
• 
  
  Again, if these two have an angle θ,
  如果这儿的角度是 θ