Question

when every thing falls downward due to gravity then why fire go upward​

Answer 1

bacause we can't fire them downward

Answer 2

Answer:

The heated air is less dense than the surrounding cooler air, and so the cooler air "squeezes out" the hot air, which moves upward. As the hot air moves upward, so does some of the still-burning material, resulting in a flame that flickers upward, away from gravity.