Understanding fire

Discussion in 'General Science & Technology' started by wegs, Dec 20, 2022.

  1. exchemist Valued Senior Member

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    Done that: no website.

    Please Register or Log in to view the hidden image!

    Oh wait, it's on his reply. Yes now I see it. Thanks.
     
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  3. trevor borocz johnson Registered Senior Member

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    The link is in the word website.
     
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  5. exchemist Valued Senior Member

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    Ah yes. And no, I don't disagree with that website.
     
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  7. James R Just this guy, you know? Staff Member

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    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.
     
  8. kx000 Valued Senior Member

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    That is true aswell, but air can not be flammable or our world would die.
     
  9. wegs Matter and Pixie Dust Valued Senior Member

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    This a very helpful explanation, thanks - so if we're seeing a forest fire for example, are (literal) atoms of oxygen combining with whatever fuel sources, to create the flames we see? Whatever is on fire would be matter, and fire would be considered energy? Matter has energy...does all matter have energy? Not sure if my questions are veering off topic...
     
  10. wegs Matter and Pixie Dust Valued Senior Member

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    I've often wondered something, James- if a member is banned for posts that are in violation of forum rules, why aren't their posts removed from said thread? I don't mind either way if you leave the posts up, but just wondering...
     
  11. exchemist Valued Senior Member

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    All matter has energy, yes, usually in several different forms (rest energy, potential energy, kinetic energy).

    I don't believe thinking of fire as energy is particularly helpful or accurate. The distinguishing characteristic of fire, compared to the many other oxidation reactions that give off heat, is the presence of flames. As I tried to explain in post 2, these are complicated phenomena involving matter in mid-reaction, heat (of course) and light. Flames involve photochemistry.
     
  12. DaveC426913 Valued Senior Member

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    Oxygen rips the organic matter apart to get at the carbons and hydrogens inside. It combines with the carbons to make carbon dioxide and combines with hydrogen to make water (CO2 and H2O are the major byproducts of combustion). These chemical reaction release heat.

    Fire is the visible byproduct of an incomplete chemical reaction.

    It's the molecules that have energy.

    The tree built its cells up from components of air, water and soil. That took energy to do - energy from the sun - and it;s stored in the bonds of the molecules of cellulose that make up the wood.
     
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  13. DaveC426913 Valued Senior Member

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    This has come up before. Trying to remove off-topic posts from the middle of a discussion tends to decimate the thread - what with all the users responding - and make it virtually unreadable. It's also a lot of moderator effort.
     
  14. James R Just this guy, you know? Staff Member

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    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.
     
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  15. DaveC426913 Valued Senior Member

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    Which is also why timely reporting by conscientious members is helpful. The sooner a contentious post is seen by moderator, the more likely it can be extracted without disrupting the thread.
     

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