I just now saw this thread.
As which of the three states (solid, liquid, gas) would fire be classified, if any? I heard a long time ago that fire is part plasma?
Fire is the result of a
combustion reaction; a carbon-based material burns in the presence of oxygen and gives off various products. The flames you see are from the reaction releasing hot gases (and heating the surrounding air) to a point where it radiates light in the visible part of the spectrum. The burning material could be liquid, solid or gas, a gas will be given off, and the light you see in the form of flames is coming from that hot gas. (Although I don't think it really makes sense to refer to fire itself as a material; it's more of the process, but that's just bickering over terminology.)
Plasma, on the other hand, is a gas that's been heavily ionized (had the electrons removed from it's molecules). This causes it to have a net electrical charge and various other properties different from non-ionized gases. The removal of the electrons requires energy to excite the molecules, which can occur through heating. So plasma could be present in fire, if it is hot enough to ionize the gas being given off or the surrounding air, but isn't required. In general the answer would be "no, fire is not a plasma."
My book says that matter has wave properties, and also that energy has particle properties. So far, this has only been explained to me on the sub-atomic level. It makes sense in that context, but I'm still trying to wrap my mind around the thought on a macroscopic level.
Yes, this is wave-particle duality, as already mentioned. 'Waves' can be detected as particles because of quantum mechanics; energy is quantized, or comes in discrete units (this is true for all forms of energy) - these units are the particle forms of the energy that we detect, for example photons. The reason 'particles' can have wave properties is slightly more complicated; in quantum mechanics the actual history of a particle (that is, it's path through space and time) can treated as the sum of all it's possible histories together, which allows for interference between the different paths it could have taken, and we get stuff like wave diffraction even for a single particle.
This still occurs on a macroscopic level, technically, but for all practical purposes the quantum effects disappear because the systems are too large and the measurements being made are not precise enough to detect them. At higher energies quantum effects become more subtle and require greater effort to detect (this is true of all systems, micro or macroscopic), but the energies of macroscopic systems are always very large, if only due to the mass-energy. For example, if you were to do a diffraction experiment with something like a car instead of a single particle, you would not get a diffraction pattern (a wave property) because the massive energy of the car will cause it's associated wave to cycle so fast as to be effectively continuous - no interference pattern is created since the 'waves' are basically constant instead of cycling. There are other explanations for why you don't see other quantum effects, like quantum tunneling, but they all basically go back to the point that quantum effects aren't noticable for high energy systems.
There are some exceptions; a few macroscopic systems do experience quantum effects, primarily
superfluids and
Bose-Einstein condensates. These have to be cooled to very low temperatures, which puts all the particles in very low energy states anyways.
(If any of this is un-understandable or the terms aren't familiar, feel free to ask. Or not, whatever.)
