What Am I Riddles

Question: I have two rings. I move by request. If the mixture isn't right I just sit and rest.

What am I?

Question: What is as big as you are and yet does not weigh anything?

Question: You struggle to regain me.
When I'm lost, you struggle to obtain me.
I pass no matter your will,
but I'm your slave to kill.
What am I?

Question: What is something that you always have with you but you always leave behind?

Question: A trail, a union, together tied.
Come across me and you will find,
you cannot change the course I'm on,
without me you cannot travel on.

What am I?