In this sentence, "While playing the tuba, Orin felt as if his world was perfect," is "playing" a gerund or a participle and why?
Here word playing is a (present) participle because it is a part of a clause describing an action (feeling). If we wanted to ask about this clause we would say :
When did Orin feel as if his word was perfect?
It could be a gerund if it acted as a subject like in a sentence:
Playing the tuba made him feel as if ...
In this fragment word playing acts as a subject so it is a gerund