Saturday, June 11, 2011

What exactly is fire?

Here is a quick little post that people might enjoy knowing about. Ever since I was a wee little child, I wondered to myself "What exactly is fire?" I knew it wasn't matter, nor could it be pure energy, something was going on that educational books and shows where not telling me. With out any answers, Internet wasn't as big at the time nor as helpful, I eventually forgot about that question but every time I saw that dancing flame blackening contorting and vaporizing what ever its fuel source was that question still beckoned int the back of my head (and yes I think I'm a bit of a pyro, but I love me some fire).

Now many years later with an enhanced knowledge of science and physics, at least more enhanced than an eight year old, I pieced together the various clues until I came to the answer! The answer lies in the physical structure of the atom itself! *Crash of Lightning* Of course the shown model of the atom is wrong, electrons orbiting around a nucleus like planets around a sun is easier to imagine than an "electron cloud" that shows the probability of an electrons position which can change based off of observation due to the Heisenberg Uncertainty principle.

A non-ionized lithium atom. Why lithium? Because Google Images say so!

So you here you can see the different shells that surround the atom. The lowest shell can only have two electrons in it at a time and the second can have eight and so on. In the non excited state all the electrons go to the lowest shell they can and fill up the next shell until all the electrons are accommodated for. How ever an electron can become "excited" and rise to a higher shell. Since this is moving away from the oppositely charged nucleus it requires energy to move away from it, much like how it takes energy to move away from the Earth. Purely randomly (I say this cautiously) an electron can settle back down from it's excited state down to it's normal state in a lower shell. This causes a release of energy which then turns into a photon. The frequency of the photon depends on how many shells the electron dropped down to, the more shells it fell the higher the frequency. 

So now what can add energy to an atom causing its electron to become excited? Heat. And the hotter a body the higher the electrons will jump when they become excited. So even in space a warm body without any other matter for the body to leak heat to through conduction, it will still cool down since it has excited electrons which throw away energy in the form of photons. So right now every object that you are seeing is releasing light constantly. So why can't we see in the dark? As I said the warmer an object is the higher an electron jumps and than when it falls the higher the maximum frequency of light it emits. At normal Earth temperatures objects radiate light in the infrared spectrum which is invisible to the human eye. And yes this is exactly how night vision infrared goggles work, they have detectors which can pick up the heat radiated by bodies in Earth like temperatures (that always confused me, I was like wait infrared is heat? But it's just a small spectrum of all light! How can it be heat?). 

The electromagnetic (light) spectrum, in case you were curious 

So now we can understand what happens when metal becomes really warm. As an electron stove turns on it's maximum frequency starts entering the lowest frequency of visible light, red, and now we see it glowing a nice red. If we continue to warm up the metal it goes through the entire spectrum and starts emitting frequencies at all visible levels which our eyes detect as white, so it's now burning white hot. If we keep on raising the temperature it will eventually start emitting ultraviolet rays, but I don't think any stoves get that hot. This is exactly how light bulbs work. You take tungsten, which is a good conductor and has a high melting point, put it in a vacuumed environment which light can still penetrate so that it doesn't burn the air and destroy itself, and than run electricity though it which warms the filament to very high temperatures therefore causing it to emit visible light. This also happens on the sun since the nuclear fission of hydrogen realeases allot of energy and heat but since it is at such high temperatures it releases light at all frequencies all the way up to gamma rays. So the sun isn't fire but is much more complicated and I'm not going to go into that in this post. 

So what exactly is fire? Well it is an an exothermic reaction between two chemicals, one is most of the time oxygen, that in order to start the reaction the fuel sources need a certain level of heat to start the process but the chemical reaction releases enough or more heat in the process to keep the chemical reaction going given that there is enough of both fuel sources to keep it up. The reactions most of the time give enough heat to radiate light at frequencies that we can see, most commonly from red to yellow. This chemical reaction also heats up the nearby air and as the heated air's density lowers due to the increased heat, it rises since the gravitational pull of the earth pulls more on the denser colder air. As the heated air makes contact with the colder air the lose heat through convection and begin to radiate heat at levels our eyes can not detect. Fluctuations in the density of air due to movement and other factors also cause the rising heated air to not go in a straight path but move around unpredictably (I heard that a super computer can not predict the movement of the flame and smoke of a match). So essentially at it's base, fire is pretty much hot air. So I hope you actually found this post helpful since fire is a pretty integral part of human life.

YAY fire in a bottle cap!

Also any questions and corrections be welcome by anyone, including you shady anons who randomly stumble upon this page.