Answer:
Used left or right, I get to travel over cobblestone or gravel. Used up, I vie for sweet success, used down, I cause men great duress.
Where humans breath liquid?
What stays the same size no matter how much they weight?
What can be big, white, dirty and wicked?
who do you think you know but sometimes you don't
People take me on walks and I run and have fun. What am I?