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  • We know that fire results from the combustion of organic material and air, but don't you

  • still sometimes wonder what fire is? Why are gas flames blue and wood-fire orange? And

  • why do flames move in such a mesmerizing way? Chemistry may tell us the recipe for combustion,

  • but the light show is all physics.

  • When a flame burns cleanly (like a gas flame, blowtorch or the base of a candle), the heat

  • excites the molecules to release light (usually pale-blue) from atomic transitions. That's

  • quantum mechanics!

  • Now when the fuel isn't as pure and doesn't entirely burn (like a wood or coal fire or

  • the top of a candle flame), there's still some blue light, but you don't see it because

  • it's overpowered by light from all the particles of soot & smoke - they're glowing red-hot!

  • So why do hot objects glow? Thermodynamics. A process called "blackbody radiation" makes

  • all objects glow with light of a color depending on their temperature. The reason that you

  • don't see your friends glowing, though, is because we're too cool to glow with visible

  • light - we glow in infrared. But lava, a hot piece of iron, or soot in a flame are all

  • hot enough to glow with that familiar red-orange light.

  • And the reason flames are shaped like tongues snaking skywards? Gravity! The earth's pull

  • is what makes hot air rise, and this convection shapes flames into their familiar form. If

  • you light a match in zero-G, the flame spreads outwards like a balloon - there's nothing

  • to tell it which way to go, so it goes in all directions!

We know that fire results from the combustion of organic material and air, but don't you

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B1 中級

火とは何か? (What is fire?)

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    Why Why に公開 2021 年 01 月 14 日
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