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PURPOSE: To demonstrate how a flame burns in the absence of normal convection.
DESCRIPTION: A candle, attached to the lid of a one-gallon jug, is lit and the lid screwed onto the upside-down jug. Throw the upside-down jug into the air and catch it or hold the upside-down jug high and drop it and catch it as it falls. While it is falling, the system inside the jar is in a weightless environment, so convection currents cease. In normal burning, the hot air rises by convection, allowing cooler air containing more oxygen to continuously feed the fire. Without these convection currents the candle should immediately go out, BUT IT DOES NOT.
On the other hand, the way that the candle burns is changed significantly, as is discussed in the web site linked below.
The NASA web site Candle Flames in Microgravity, from the Glenn Research Center, Cleveland, Ohio, had some interesting photographs and discussion that cleared up this question, but it has been removed from the NASA web site. The photograph below was taken from this document.
Another NASA paper, Not Just Another Old Flame, discusses this problem and has photographs of a candle flame in gravity and in a microgravity environment.
SUGGESTIONS: It is a common myth that a candle flame will go out in the absence of gravity, such as in an earth satellite or a space ship in outer space. This is apparently not the case, as becomes clear when you revies the NASA document linked above! On the other hand, using fire in this environment may be very dangerous because the atmosphere is richer in oxygen than the normal earth atmosphere. See Question of the Week #261 for information on using this demonstration to enhance class involvement.
REFERENCES: Available. (PIRA 1G20.10)
EQUIPMENT: Glass jug, candle and matches.
SETUP TIME: 10 minutes.
