Oxygen and Nitrogen make up a significant part of the atmosphere. Fire always stretches upwards, assuming no wind, leading me to believe it’s less dense than air. Oxygen is highly flammable. That should be everything fire needs to sustain itself while flying away into the sky.
In: Chemistry
The fire is tied to the fuel source, like a log, which is burning. The visible flame which you see is a result of the combustion occurring at that fuel source. This results in heat and light. The heat rises, making the flame travel upwards.
The oxygen by itself can’t burn without the fuel source (which is fortunate, otherwise we’d all be dead of self-sustained skyfire).
So as the flame moves away from the fuel source, there is no longer any reaction generating heat or light and the visible flame dissipates as its energy radiates away.
Fire is weightless, and it does float away. As it floats away from the heat, it stops glowing and becomes just regular gases in the air. The stuff floating up from the fire was part of the fire, once. It needs the fuel to keep burning, glowing, etc. so as it goes up, it stops being fire.
You’re thinking about fire as a physical object. Let’s look at what fire really is. When something burns, it’s chemical structure breaks down. It gives off gases when it gets hot enough. Think of it like boiling a lot of water and seeing steam. Now when it gets really hot, those gases glow. That glow is what you call fire. It’s not much different than the electric burner on your stove glowing. On a cool burning fire, like a candle, you can pass a finger through the flame without injury. On a hot burning fire, you can pass through the gases/smoke and get burns even if you’re not in the actual fire.
In the case of an electric element in a stove, you can have it hot enough that it glows without actually burning. On the flip side, you can have something burn without being on fire. Certain chemicals have “invisible” flames which is just hot gas that’s burning but not glowing.
Those gases do go into the atmosphere. You can see smoke rise very high. The bigger and hotter the reaction, the larger the flames. But why don’t we see flames rising thousands of feet with the smoke? Because it cools down. Look at that pot of boiling water again. Stand on a chair, and put your hand above it. Then get off the chair, and stick your hand in the pot of boiling water (well actually don’t do that.) You can feel the difference in temperature. It’s much cooler the farther away you get. Remember, since the fire is simply really hot gas, when it cools down, it stops being fire. If you keep those gases/smoke close to the fire, and hot enough, like in a house, the smoke can, and does burn. But let it into the atmosphere, and it’s simply not hot enough to glow.
Fire stretches upwards because it heat the air, which make the air expand, more less dense and rise up, dragging the fire with it. But that’s only work in gravity, because without gravity you don’t have buyouncy and the denser cold air won’t go down pushing the hotter less dense air up.
Here a video about that.
[https://www.youtube.com/watch?v=BxxqCLxxY3M](https://www.youtube.com/watch?v=BxxqCLxxY3M)
Fire also needs fuel – the substance which is being burned.
The flames we see are the visible part of the chemical process of burning, and they basically *are* trying to float away.
The reaction is tied to the fuel source, so as flames rise away from their source, they go out.
The greater the fuel supply and the stronger the reaction, the farther away flames can spread.
Fire occurs when a chemical reaction produces enough heat the surrounding air is hot enough to glow in wavelengths our eyes can see. Once you get far enough from the reaction, the air cools to the point it no longer gives off that light.
Oxygen is not “flammable” but it *IS* an oxidizer, which means it makes any *existing* fire more intense.
And when you see a fire, you are actually seeing the fumes burning, not the actual wood or whatever. The heat from the fire causes the fuel to give off flammable gasses, those gasses burn, which increases the heat, which causes more gasses to be given off, in an endless circle until there is no more gasses to be had. In that process, it damages the wood or other fuel provider and reduces it to ash.
So the fire relies on those gasses to burn, and that’s why it stays firmly in place and doesn’t fly off into the sky.
What you see as fire is the light released by plasma, ionised gas produced by the combustion reaction. Electrons in the atoms of gas are excited to a higher energy level by the energy released in the reaction and when they fall back down they release photons, light. This is why fire can be different colours, as the frequency of light released is dependant on the amount of energy the electrons transition by. Higher energy corresponding to high frequency, shorter wavelength light (blue and purple). This is the same reason you can see hot things with an infrared camera, as warm bodies will be releasing light in the infrared range of frequency
Fire needs fuel, oxygen and a heat source to burn. Take one away, and the fire goes out. So the flames itself are little tiny pieces of hot fuel floating through the air and getting consumed by the oxygen. They float away, get consumed and go out when either the fuel is gone or they cool down too much so they won’t stay lit anymore. Oxygen itself isn’t flammable. Oxygen is just what makes a fire possible.
First of all, you need three things for fire to happen, heat, fuel and oxygen. Oxygen is not a fuel but provides a required component to the equation. Take away any one of these three components, and you can’t have fire.
Fire is a reaction, and during that reaction, some molecules release ~~are transformed into~~ their energy, in this case, heat and light. The fire itself is essentially mass-less. But the mass of the oxygen and fuel is being transformed into other compounds. ~~energy~~.
Edit: Oversimplification led to inaccuracy.
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