I heard that ba (吧) can be used at the end of a sentence just like ma (吗). Per my understanding, it's not interchangeable with ma (吗) but a more playful way of asking the same question. (Some girl said I should use 吧 when asking her if she wants to go to lunch, idk what that means.)
So, when do you use each of these words? What are the connotations of each?