How Does Gravity Affect the Shape of a Flame?

Gravity affects the shape of a flame by anchoring down the colder air at the base of the flame, while the heated gas rises up, resulting in a teardrop shape. This effect is known as buoyancy, or the floating of less dense materials in liquid and gas. In space, flames are shaped like round spheres and are commonly referred to by scientists as flame balls. This shape occurs because the heated gas of the flame expands in all directions in the weightlessness of microgravity instead of rising upward.

More about gravity and flames:

  • A flame ball in space is much weaker than a standard flame on Earth. For example, a flame ball generally produces about 1 to 2 watts of thermal power. A birthday candle flame on Earth is about 50 to 100 watts.

  • The US National Aeronautics and Space Administration (NASA) started examining flame balls in 1997 in a study known as the Structure of Flame Balls at Low Lewis-number (SOFBALL) experiment, in which astronauts purposely lit flames in sealed chambers aboard space shuttles to determine their behavior.

  • Smoke detectors are normally placed on ceilings because the heat from fires rises upward. On spacecraft, smoke detectors typically are placed within all ventilation systems.

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