What Am I Riddles

Question: I am shorter when I stand and taller when I sit.
Sometimes I'm even called a pit.

What am I?

Question: If a man carried my burden, he'd break his back.
I am not rich, but I always leave silver in my track.

What am I?

Question: I have roots that nobody sees,
I'm taller than any trees,
up and up I go,
but I never grow?

What am I?

Question: When you bend me I'm kind
But I'm very hard to find
I'm easily sold
and rhyme with this when told

What am I?

Question: I support the fallen (ones) I restrain the naughty (ones) I replace the nonexistent (ones) What am I?