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Asked by Ashleigh to Daniel, Maggie, Ry, Scott on 15 Nov 2017.
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Ry Cutter answered on 15 Nov 2017:
Ohhh this is a good question.
So lets start with how combustion works with gravity. Fire burns oxygen (see what causes fire question). Because the air holding the fuel is heated up it becomes less dense. This means air holding more oxygen (more fuel) comes down increasing the height of the flame. (Really, it’s the hot air floating up due to the buoyancy force). If we were to increase gravity, the cold air would sink faster which would make the flame even higher!
If we do the opposite and lower gravity the flame will get smaller and smaller. If we go into space where there is no gravity the flames turn into a small sphere! The flame burns far more efficiently as oxygen is drawn to the flame. An interesting study was done called FLEX, which was designed to see how we can put fires out in space. They found that fires continue to burn in space even without a flame! The fire is too cool to see, we still can’t explain why this happens.
Here’s a video of fire in space:
Awesome question,
Ryan 😀
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Maggie Lieu answered on 15 Nov 2017:
Fire on earth goes up because of gravity. The heat from the fire heats the surrounding air, and because hot air rises, and new cold air comes in to replace it from the bottom.
Without gravity, fires become flame balls like this one:
This is because in space the new cold air comes in from all directions.
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Scott Melville answered on 16 Nov 2017:
Aww man, the others beat me to the punch! Fire in outer space is literally one of the coolest things ever. I mean, the Sun is basically on fire, right? Ever wondered why it’s a big sphere, instead of being.. y’know… more ‘fire-shaped’? It’s because in space, fire spreads out in all directions like a bubble – there’s no ‘up’ or ‘down’ so it doesn’t know any better!
P.S. This was actually my very first interview question when I applied to study physics at university – so it has a special place in my heart 😉
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