If you’ve got 90 seconds to spare the video above will explain what fire is. It’s an excellent watch, and one that might get you hooked on the Minute Physics YouTube channel.
It might seem like the sort of question a child would ask, but “what is fire?” probably isn’t something you could answer so easily. Sure, there is the text book explanation, involving plasma and something about a chemical process with oxygen, but that’s probably not the explanation most people (definitely not a child) are looking for. The video is quite good at explaining fire in practical terms, or at least more practical than CH4 + 2O2 → CO2 + 2H2O + energy (an example of a chemical process for combustion).
Much of the video is spent talking about the fact that fire glows. This happens because the heat excites molecules, causing light to be released, but did you know that normal candles and lighters (etc.) have a blue glow, but it’s too faint for you to see it? Or that all hot objects glow in some form or another? This isn’t exactly life-changing knowledge but it’s the sort of cool science stuff we (and probably you too) can’t get enough of.
At the end of the video one of the most interesting fast is revealed. We all know that fire move upwards because of gravity, but what would happen in the absence of gravity? Check out the images below of flames burning in microgravity–they lack the teardrop shape we expect to see in a burning flame and simply radiate outward from the center point.
Here is another amazing image of a flame burning in microgravity: