what is different between pain and ache ?

There is a subtle difference between "pain" and "ache". "Pain" is an unpleasant sensory and emotional experience caused by damage of tissue of the body. It is a "strong discomfort" which is sudden and difficult to ignore. Pain can be physical or mental. Generally we use "pain" when one suffers from strong discomfort like broken leg, body injuries, physical and emotional abuse etc. "Ache" is also a discomfort but it is mild, continues for sometime. Generally it can be ignored. Stomachache, Headache, Toothache , Backache are some of the examples of "Ache". All these discomforts are mild and continues for sometime but they can be ignored. I would like to add one more word which is associated with "pain and ache" that is "hurt". "Hurt" simply mean "injury" or "to injure". "A hurt person will have 'pain' and 'aches'." Consider below example to illustrate all three words. When I fallen from my bike, my leg got "hurt" badly. I felt intense "pain" in my leg. It was happened a month ago. Presently I'm fully recovered and there is no pain in my leg. However, if i think about that gloomy situation, I will get a "headache"!. I hope your doubt clarified!