We recently came across a fun MinutePhysics video on YouTube called “What Is Fire?” and wanted to pass it along. The video gives a quick, clear overview of why flames look the way they do on Earth, both in terms of their color and their shape.

Most people know that fire comes from the combustion of organic material and oxygen. We also know that the part of a fire that we see is called a flame. But what makes some flames look orange or red while others look blue? And what about their shape?

As is described in the MinutePhysics video, the color of a flame depends on how cleanly that flame is burning. Gas flames and blowtorches, for example, burn quite cleanly. In instances like these, the heat from the fire excites the surrounding molecules to the extent that they release a pale, blue light due to atomic transitions.

In the case of flames from objects like wood or coal, the fuel isn’t as pure and doesn’t burn as cleanly. In these cases, particles of soot and smoke glow red-hot and obscure the blue light.

The video goes on to explain that hot objects glow because of black-body radiation. In fact, all objects glow, but the color of that glow depends on their temperature. Humans, for example, glow in infrared and so we can’t see our glow with the naked eye. Soot in a flame, though, is hot enough to glow red-orange.

Finally, we learn in this video that flames are shaped the way they are because of gravity, which makes hot air rise. Without gravity, the flame around a match would be shaped more like a globe or a balloon.

For more handy science videos, check out the MinutePhysics YouTube page. For more information on fire and fire prevention, Harrington Group is happy to answer your questions. Give us a call!