Answer:
What is harder to catch the faster you run?
I come with a train and go with a train and the train doesn't need me but can't go without me.
As a stone inside a tree, I’ll help your words outlive thee. But if you push me as I stand, the more I move the less I am.
Light hides me and darkness kills me. What am I?
I go around in circles, but always straight ahead, never complain, no matter where I am led.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?