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Fire - what is?

  1. Jun 18, 2007 #1
    If every thing is either 'solid', 'liquid' or 'gas' then what is fire?

    Best,
    wirefree
     
  2. jcsd
  3. Jun 18, 2007 #2

    berkeman

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    What would your answer be?

    Looks to be a combination of either solid+gas (solid fire) or liquid+gas (liquid fire). Depends on what fuel material is burning:

    http://en.wikipedia.org/wiki/Fire

    Remember the fire triangle -- heat, fuel, oxygen.
     
  4. Jun 18, 2007 #3

    chroot

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    First, everything is not solid, liquid, or gas. There are many other forms of matter, such a plasma. The flame you see is, in fact, a partial plasma. It's composed of gas atoms, some of which have electrons stripped from them. The recombination of these free electrons with the atoms is what produces the visible light.

    - Warren
     
  5. Jun 18, 2007 #4

    berkeman

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    Oh, good point! I spaced the plasma part of it. Kind of like your avatar....:biggrin:
     
  6. Jun 18, 2007 #5
    I know about solids, liquids, gasses and plasmas. What other forms of matter exist?
     
  7. Jun 18, 2007 #6

    chroot

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  8. Jun 18, 2007 #7

    Danger

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    Einstein-Bose condensates, degenerate matter (such as in a neutron star)... but I'm not sure if they're really considered 'states' in the official sense of the term.

    edit: Holy cats, Chroot. That list is making my eyes hurt.
     
  9. Jun 18, 2007 #8

    chroot

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    Of course they are. Even simple things like their pressure-volume relationships are distinctly different than 'ordinary' states like gas and liquid.

    - Warren
     
  10. Jun 19, 2007 #9
    Just don't remember being taught that in school. :grumpy:

    Appreciate that, chroot!
     
  11. Jun 19, 2007 #10

    Gib Z

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    Wow I have a feeling most people here know about the things on the list, but just didn't consider them to be categorized as their own state of matter! Thats definitely what i thought of Amorphous solids.
     
  12. Jun 19, 2007 #11

    mgb_phys

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    It's not a very useful question - it's a bit like "how many seas are there".
    I would say that there are solids,liquids,gases.
    Once you start adding Bose-Einstein condensates etc then you have to pretty much have a different state for each material. A metal is different from a glass so are they different states of matter?
    I would argue that even plasma is just a charged gas - it behaves differently to a gas but then so does a magnetised solid.
     
  13. Jun 19, 2007 #12

    chroot

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    Again, plasma is a distinct state of matter, because several physical quantities (like heat capacity) change abruptly when moving from the gas state to the plasma state. Futhermore, there's a jump in free energy between a gas and a plasma -- you have to add energy to dissociate the atoms.

    - Warren
     
  14. Jun 19, 2007 #13

    mgb_phys

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    There's also a pretty impressive change when helium goes superfluid!
    I don't know if plasma is more fundemental jus because it was discovered earlier.

    My point was that 'states of matter' is not as useful a distinction as it used to be now that we know about macroscopic quantum effects.
    It's a bit like the 'number of planets' question - do you count every rock, is Pluto a planet - arguing about where the boundary lies doesn't really tell you much about orbital mechanics.
     
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