Answer:
If a man carried my burden, he would break his back. I am not rich, but leave silver in my track.
What has a bell but isn't a church. Is full of air but is not a balloon?
This thing runs but cannot walk, sometimes sings but never talks. Lacks arms, has hands; lacks a head but has a face.
You will find me with four legs, but no hair. People ride me for hours, but I don't go anywhere without needing to be tugged. Jerked or turned on, I always manage to be ready for work.
I have legs but walk not, a strong back but work not. Two good arms but reach not. A seat but sit and tarry not.
You use it between your head and your toes, the more it works the thinner it grows.