Answer:
Forward Iām heavy, but backwards Iām not.
Dies half its life. Lives the rest. Dances without music. Breathes without breath.
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.
I am the tool, for inspiring many. Buy me in the store, for not much more than a penny. Don't overuse me, or my usefulness will go.
I am round as a bowl, deep as a tub, but all the world's water couldn't fill me up.
People take me on walks and I run and have fun. What am I?