Answer:
I twist and turn and leave a loop. What am I?
I help engines spin and pants stay up
I break down buildings, I crumble mountains but you can't see me. What am I?
I have skin, more eyes than one. I can be very nice when I am done. What am I?
I am of several different kinds, but the one you pick doesn't do its job. What am I?
The more of me you take, the more I appear behind you. What am I?