Molecular friction will cause just about anything to burn if the friction is extremely high.

The only hold back would be liquids and gasses.

BTW this idea came from the firestarter movie. Totally different and far older movie.

That’s my favorite show I’m watching it over and over again

Uncle Iron describes it a couple times; basically it's the bodies energy, and it's being released. It doesn't have to be fire, it can be heat, like when he warms his tea. And then, for advanced fire benders, they seperate their positive and negative energy and the imbalance makes lightning. Or something like that. He tells Zuko something about it to prepare him for Azula.

As someone who just watched the show for the first time a few months ago, I was inclined to agree. The obvious counterpoint is "It's an element, so it should be present in everything", but then how do you explain the Fire Nation trapping earthbenders on an oil rig? It may be that the fire they conjure is just a condensed form of a more general energy, but that seems like a stretch.

I've heard the idea that the Classical elements didn't represent elements in the sense of "constituent substances" but something more like "states of matter", since they correspond to solid, liquid, gas, and well, other gas, but ancient Greeks didn't know that. I'm on-and-off looking through texts from that time and place to try and get a firmer answer, but I suppose it WOULD make more sense to coalesce loose energy into a more energetic material form (i.e., fire) than to a more concrete one.

I'm not sure it does explain it. It may be like how the blood bending woman told Katara she can draw water from the air.. mayhaps firebenders transmute the atomic elements to create a combustion reaciton.

Also.. nice lipstick, love the goth look :)