Answer:
I am heavy forward but backward I'm not.
Crooked as a rainbow and slick as a plate ten thousand horses can't pull me straight.
My head bobs lazily in the sun. You think I'm cute for my face is yellow my hair is white and my body is green.
I can be repeated but rarely in the same way. I can't be changed but can be rewritten. I can be passed down, but should not be forgotten. What am I?
Without a bridle, or a saddle, across a thing I ride a-straddle. And those I ride, by help of me, though almost blind, are made to see. What am I?
Give it food and it will live, give it water and it will die.