Does hot air rise because it is less dense than cold air and if so, what would a match burning in zero gravity look like, i.e. – what is the effect of gravity on fire?
You’re right on when you say that hot air rises because it is less dense than cold air, and indeed a flame in low gravity looks very different than the familiar teardrop shape that we see on birthday candles or on a match. In fact in microgravity, the flame is actually round, as there is no convection to distort its shape. Oxygen has to get to the flame by diffusion, and if the diffusion is not fast enough, the flame may actually go out. A great deal of combustion/burning research was done this summer aboard the MSL-1 mission flown in July, and we actually have many pictures on the MSL site related to combustion. You can find these images and much more information at the following URL: http://science.msfc.nasa.
