Answer:
I help engines spin and pants stay up. What am I?
I’m tall when I’m young. I’m short when I’m old. I can light up your world. What am I?
I wiggle and cannot see; sometimes underground and sometimes on a tree. I really don't want to be on a hook and I become a person when combined with “book”.
I open to close but I close to open. I'm surrounded by water but I'm never soaking. What am I?
Flat as a leaf round as a ring. I have two eyes but can't see a thing.
What is yours but only used by others?