on a cool night with no wind people facing a campfire feel a breeze on their backs. why?

Answer 1

I answered this for maphette below:
physics - Damon, Sunday, December 1, 2013 at 7:18pm

The campfire is hot
The air above the fire is hot
so its density decreases
so it rises
air rushes in from all sides to replace it
as it rises.

Sail much?