1. I tripped over a root and scraped my knee.2. When I was walking down the street, I slipped on a banana peel and fell on the ground. Thankfully I was alright.
 trip over/on something slip on something falltrip over/on something = 採到什麼而跌跤slip on something = 採到什麼而滑倒fall 指實際的倒下的動作。
The janitor neglected his duty on the day the robbers broke ino the school.