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Name: Chris
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Question:
My roomate and I were wondering what happens to an open flame from a match or lighter in microgravity? Will it still take the shape of an up-side-down water drop? We assumed gravity played a part in the shaping of a flame.



Replies:
Dear Chris,

A normal flane from a match (or lighter) takes the shape of a tear drop because the flame heats the air next to it causing an upward convection current of air since the heated air is "lighter" = less dense than the surrounding cooler air. The less dense air the feels a buoyant force as Archimedes discovered long ago.

If there were no gravity, the weight of the dense and less dense air per unit volume would be exactly the same -- zero. So there would be no convection current. Since there is then no preferred direction (no "up"), the flame would assume a spherical shape.

Incidentally, this means that the flame would be extinguished very quickly as soon as it consumes all the oxygen in its immediate vicinity. If you are in an elevator holding a lighted match and the flame becomes spherical and then goes out, you should worry!

Best, Dick Plano, Professor of Physics emeritus, Rutgers University


Chris,

I have seen this question somewhere before, and the consensus was that in a perfect enviornment, free from drafts or gravity, the match would quickly burn itself out as it consumed all of the immediately available oxygen. the reason for the teardrop shape is that the air immediately around the match head grows so hot that it begins to rise very quickly, while glowing brightly. As it rises it also cools, and the incadecent area quickly shrinks to a point.

Without gravity, it is impossible to define buoyancy, without which there is no pressing need for the air around the match stick to rise. Given that, I suppose the flame would appear spherical, while it lasted.

Ryan Belscamper



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