Understanding fire

Moderator note: trevro borocz johnson has been warned (again) for posting pseudoscience in the Science sections.

Due to accumulated warnings, trevor will not be rejoining us until the new year.

 

wegs,

Yes. Fire is (just) a chemical reaction in which oxygen combines with something else, releasing some chemical energy in the form of light and heat. Our atmosphere is unusual in that it has a large amount of free oxygen molecules, which are actually quite chemically reactive. Fire usually requires a small "kick" of some kind to get the reaction going (chemists call this "activation energy", IIRC), but once it is going the released energy will continue to spark further reactions as long as the fuel source and the oxygen holds out.

The light you see from a fire is emitted from atoms or molecules, including some that are released into the air. Typically on Earth the released heat causes the air above the fire to become less dense, which is why fire goes upwards.

The light is actually produced by atoms or molecules becoming excited due to energy released in the chemical bonding of oxygen to something in thWe fuel source. Those excited atoms or molecules quickly fall back to their more stable ground state energies, releasing light in the process.

Energy itself is not a substance, so it makes no sense to say something like "fire is energy". Energy is just a number. We can total up various (invented) kinds of energy for substances before and after a reaction. When we include all of the "kinds" of energy, we happen to find (if we use the correct calculational rules) that the number we call "total energy" is always the same before and after a reaction, which is why the concept of energy is useful at all. People in movies often refer to mysterious glowing things as balls of "energy", but that makes no sense at all. Energy isn't stuff. Energy can't be a ball or a cube or any shape. It has no shape. It's just a number. Similarly, the term "energy" is widely misapplied in pseudosciences (e.g. "healing energy", "spiritual energy", "life force energy", "qi energy"), in which the mental picture still tends to be of a flowing "aura" or ball of indeterminate light, or similar. None of those things is energy. Energy is much more boring than that, in reality.

Yes, but in a very technical and specific sense. "This flying tennis ball has energy" really means only that "if we calculate some numbers in a particular way, according to some theoretical rules, we can use the total number, which we call the energy of the ball, to work some stuff out about how the ball will behave or interact with other things around it". So, in physics, there's a formula to work out a number associated with the ball's speed, which is given the label "kinetic energy". There's another formula to work out a number associated with the ball's mass, which is given the label "mass energy". There are other numbers we can associate with the ball's spin, the atoms in the ball, etc. etc. When we add all these numbers up, we get a notional total that we call "the energy of the tennis ball". But the important thing to appreciate is that giving the ball some numbers isn't adding anything physical to the ball. It's just an idea in our heads.

Dave answered above. Briefly:
1. Deleting posts often upsets the context of the thread, especially if people have replied to posts that are later deleted.
2. It is preferable to keep a record showing the reason that an official warning is given, otherwise disgruntled moderated members tend to complain that the warning was issued unjustly.
3. Leaving posts alone is useful to show other readers of examples of the kind of thing that will be likely to attract moderator intervention. This is useful public messaging.
4. It requires moderator time and effort to delete or move posts around, and doing so without destroying the flow and context is often difficult or even impossible, especially when others have replied.