来自《耶鲁大学开放课程：基础物理 第1集 第1集》

• 
  
  that a was a constant of -9.8 or -10 is wrong.
  加速度为常数-9.8或-10——就不成立了
• 
  
  So that's another thing to remember.
  所以这点也要牢记
• 
  
  Once you get a formula,
  使用公式时
• 
  
  you've got to always remember
  你一定不能忘记
• 
  
  the terms under which the formula was derived.
  公式使用的前提条件
• 
  
  If you blindly use it beyond its validity,
  如果超出适用范围 盲目使用
• 
  
  you will get results which don't make any sense.
  你得到的结果就毫无意义
• 
  
  Conversely, if you get an answer
  反过来说 如果你得到一个结果
• 
  
  and it doesn't seem to make sense,
  发现似乎是错的
• 
  
  then you've got to go back and ask,
  那么你就应该回过头来问问自己
• 
  
  am I violating some of the assumptions,
  我是不是违反某些前提了
• 
  
  and here you will find
  这个模型中 你就发现