break down和break up都表示“分解”时，怎么区别？ 高手帮忙啊！谢谢

break down: 1) if a car or a machine break down, it stops working. 2)to fail. 3) if someone break down, they start crying. 4)if you break down a door, you hit it so hard that it breaks and falls to the ground. 5) if a substance breaks down, or if something breaks it down, it changes or separate into smaller parts as a result of a chemical process
break up: 1)to separate something into smaller parts. 2) if somethingbreaks up, or if you break it up, it breaks into small pieces. 3)to end a relationship with a husband, wife. 4) to stop a fight or argument. 5) if a meeting or party breaks up, people start to leave. 6) when a school break up, it close for a holiday.