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

On a cool night with no wind, if people facing a campfire feel a breeze on their backs, it can be attributed to a phenomenon known as the "chimney effect" or "chimney draft." This occurs primarily due to the temperature difference between the air near the campfire and the surrounding atmosphere.

Here's a more detailed explanation of how the chimney effect produces the perceived breeze:

1. Temperature difference: When a fire is burning, it releases hot air and smoke. The hot air rises due to the temperature difference between the fire and the cooler surroundings.

2. Air displacement: As the hot air rises, it creates an area of low pressure near the fire. This low-pressure zone acts as a vacuum, drawing in surrounding air to replace the rising hot air.

3. Air movement: As the cooler air is drawn towards the fire, it creates a flow in a vertical column. This air movement can eventually reach the people facing the fire, resulting in a perceived breeze on their backs.

It's important to note that this airflow is not caused by any external wind but rather the movement of air caused by the heated air rising from the fire itself.

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?