Do You Know?

1. I know that planets rotate on their own axes. Why does this happen?  Are there any special forces that cause this?
2. I heard somewhere: A human can survive 3 minutes without air, 3 days without water, and 3 weeks without food. How long can one really survive without food or water?
3. How does a flame look in zero gravity?
4. Did travellers in the past actually depend on the North Star to guide them?  How could they use its position?