Flame in Microgravity
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.
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
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.
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Update: June 2012