What Am I Riddles

Question: I am an instrument that you can hear, but you can not touch or see me.

What am I?

Question: Half of those who read this riddle, I am your best friend.
I depend on you, but it's you I will defend.

What am I?

Question: I stand in one place yet I fill a whole room.
I can be filled with molten rock and come in every hue.

What am I?

Question: I'm the eyelid to your life and hide you when you're inside.
You can draw me and you can pull me, but you must leave to see my good side.

What am I?

Question: I'm in everybody but everybody still wants me.
I won't feed you but I'll feed the tree.

What am I?