Fire - what is?

[wirefree]

If every thing is either 'solid', 'liquid' or 'gas' then what is fire?

Best,
wirefree

[berkeman]

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.

[chroot]

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

[berkeman]

Oh, good point! I spaced the plasma part of it. Kind of like your avatar....:biggrin:

[Repetit]

First, everything is not solid, liquid, or gas. There are many other forms of matter, such a plasma.

I know about solids, liquids, gasses and plasmas. What other forms of matter exist?

[chroot]

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

- Warren

[Danger]

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.

[chroot]

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.

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

- Warren

[wirefree]

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

Just don't remember being taught that in school. :grumpy:

Appreciate that, chroot!

[Gib Z]

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.

[mgb_phys]

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.

[chroot]

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

[mgb_phys]

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.