not obliged to do /obliged not to do区别

问题描述:

not obliged to do /obliged not to do区别
请问这两个短语在意思上的区别是什么啊?

1
be obliged to do sth 不得不做某事,一定要做某事 =feel obliged to do sth
be not obliged to do 不是一定要(非要)做某事
2
one oblige another to do sth 某人迫使另外一人做某事
.not to do sth .迫使不让他做某事
be obliged to do sth *做..
.not to do *不能做...