Fire seems almost like magic. What is it exactly? Chemistry tells us that fire is the energy released from the chemical reaction between oxygen and organic material. This is known as combustion. This energy is released in the form of heat and light. But chemistry only goes so far in our understanding. Why does fire acts the way it does? Here's where physics comes into play.
Examples of combustion equations
Physics not only explains the shape fire takes but also why certain flames glow in different colors. Gravity makes warm air rise and this principle is what shapes the flames into their distinct shape. In fact scientists at NASA have done experiments with flames in zero gravity and the flame actually spread out in a spherical shape as seen below:
As for the light we see, physics explains this too: specifically quantum physics does. The heat from the reaction excites the molecules to emit light of a certain color, in most cases blue. Red flames are actually heated up ash and soot around the flames glowing and can sometimes cover up the blue light from the actual reaction.