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Name: Digant P.
Status:  student
Age: 15
Location: N/A
Country: N/A
Date: 2/18/2004


Question:
How many states of matter are there?


Replies:
This is a more involved question than it first appears. The "simple" answer is that there are three -- solid, liquid, and vapor -- however, Nature is not quite so unimanginative. Some substances have more than one solid phase, depending upon the temperature and pressure. Water, for example, has 13 solid phases at last count. Some liquids, helium for example has two liquid phases -- "normal" helium above about 2.4 K and a superfluid phase below that temperature. Above the critical temperature and pressure, a substance has only a single fluid phase. If you consider a substance that is a superconductor different than the same substance that is a "normal" electrical conductor, a lot of substances have multiple solid phases. At sufficiently high temperatures, substances occur as ionized charged species called a plasma. The properties of a substance that is a plasma are certainly different from the same substance that is not composed of ions, so that could be considered a different state of matter. So called "liquid crystals" have different liquid phases depending upon the orientation of molecules in the liquid state.

You can see that your question depends upon how you want to define a "state of matter".

Vince Calder


Digant,

States of matter in classical physics are solid, liquid, and gas. Plasma, the collection of charged gaseous particles containing nearly equal numbers of negative and positive ions, is sometimes called the fourth state of matter. I hope that this helps.

Sincerely,

Bob Trach


Three or four, depending on who is telling you: Solid, liquid, gas and plasma. In school, students often learn about the first three, and plasma is only mentioned.

Pat Rowe


I do not think it is a completely definable number, Digant.

Imagining a given lump of matter, and working from low temperatures to higher and higher temperatures, matter falls apart one stage at a time. We find: solid, liquid, gas, plasma, nuclear particles, and quark soup. Instead of quark soup, matter could be dissolved into photons of light. Increasing pressure instead of temperature, one can reach neutronium and spacial singularities (black holes). So far that is about nine. There could be a couple more. Some striking cryogenic states might qualify too. All might be called states of matter.

At some high temperature stage the chemical identity of the matter is irreversibly changed: when you cool down. it is no longer the same stuff. That is usually true for plasma, and sometimes true for gas. So both 3 and 4 have their reasons for being adequate answers. Whether your favorite set is

3: {solid-liquid, gas} or
4: {solid, liquid, gas, plasma},

is kind of up to you.

If you are inventing conceptual categories of mechanical behavior when you push on it, perhaps it is a little better:

solid: constant shape, volume, and mass

liquid: constant volume and mass, variable shape

gas: constant mass, variable volume and shape (includes plasma)

black hole: constant mass,no definable volume or shape!

(The mass is all concentrated at a point in the middle.) never pushes on anything, only pulls... (but then, a swarm of black holes is almost a gas...) Perhaps category 4 should be "point-like particle"?

here, have a fuzzy limit!

Jim Swenson



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