Fun Riddles

Question: He has married many women, but has never been married. Who is he?

Question: A cowboy rode to an inn on Friday. He stayed two nights and left on Friday. How could that be?

Question: Many have heard me, but nobody has seen me, and I will not speak back until spoken to.What am I?

Question: When you need me, you throw me away. But when you're done with me, you bring me back.

What am I?

Question: What is the center of gravity?