What Am I Riddles

Question: When you do not know what I am, then I am something. But when you know what I am, then I am nothing. What am I?

Question: I go up and I go down,
towards the sky and the ground.
I'm present and past tense too,
Let's go for a ride, me and you.

What am I?

Question: I have no wallet but I pay my way.I travel the world but in the corner I stay.

What am I?

Question: What is thrown to both kings and beggars?

Question: My eye is dark,
and my mane is yellow.
You man see me at the mart,
and I'm probably taller than you fellow.

What am I?