What are the difference between refrain and restrain?

Restrain and refrain has same meaning “stop yourself or a person doing something “. 
However, if you are using “restrain”, you are stopping yourself or the person with force 
which could be mentally or physically both. For example- “ police had to restrain the crowd
 using tear gas.” or “ I couldn't restrain myself to talk back to her.” On the contrary,
 refrain doesn't show any force. It indicates doing something which one isn't supposed to do. 
For instance- “the students should refrain from gossiping during the class." or 
“you have gained weight so you must refrain from eating oily food”.