Answer:
I start with an E end with an E and have a letter in me.
Never resting, never still. Moving silently from hill to hill. It does not walk, run or trot. All is cool where it is not. What is it?
I am the key that is the hardest to turn
What force and strength cannot get through I with my unique teeth can do.
I'm the source of all emotion but I'm caged in a white prison.
I am rarely touched but often held. If you are smart you'll use me well. What am I?