ELI5 : why isn’t plasma considered a liquid or a gas? I get that it’s a 4th state of matter and it’s conductive, but i don’t get why it’s not considered a conductive liquid or gas.
ELI5 : why isn’t plasma considered a liquid or a gas? I get that it’s a 4th state of matter and it’s conductive, but i don’t get why it’s not considered a conductive liquid or gas.
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It is considered a fluid, like all liquids and gasses are. The division of matter into three or four states is a very aged concept that persists in education, but as soon as you get to real physics/material science, things get much more interesting. (fun fact: there are even 21 different states ice can be in!)
Because it’s so energetic that it’s ionized, which gives it different properties than a gas.
Liquids and gases are still made up of atoms — that is, the particles are made up of nuclei and electrons bound together.
Plasmas are different — the electrons and nuclei are no longer bound to each other, and this difference is important.
Further, gases and plasmas have different properties when it comes to electrical conductivity and how their constituents interact.
Plasma isn’t a gas because the molecules that make up a plasma are fundamentally altered and don’t behave like a liquid or gas. Rather than colliding, molecules in a plasma move as a unit in waves; gases are insulators, while plasmas are conductive; and the particles that make up a plasma don’t behave the same as the mass difference between ions and electrons is vastly different.
Essentially, plasma works differently enough from a gas that we call it plasma instead.
All gases and liquids have attractive forces between atoms or molecules that, at least to some degree, offset their desired to fly away from each other. Those forces depend on the structure and size of electron orbitals. Since there are no electron orbitals in plasma, those forces don’t exist. Conversely, electric and magnetic fields DO affect the motion of plasma, whereas they (mostly) don’t affect gases
The main thing I consider when thinking about plasma vs. other states of matter: is the electrons are free-flowing (decoupled). It’s just a soupy mess of nuclei rumbling around with a bunch of electrons flying around them.
Words mean things, but when it comes to any sort of category a lot of times we have to think of the words as descriptions more than definitions.
I’ll give you another example: what exactly is “furniture?” According to the Oxford definition, a couch isn’t furniture any more once you move it outside, and according to the Merriam-Webster definition a kitchen sponge is furniture, but both of those statements would seem very silly to most English speakers.
Anywho, the phases of matter are like that. The words “solid”, “liquid”, “gas”, and “plasma” don’t describe everything, and you could make arguments that some things kind of fall into multiple categories. The borders aren’t terribly well defined, and if they are well defined they aren’t terribly useful.
Phases is just another word to broadly describe things. Whenever you get specific, like utilizing plasma, the idea of phases becomes quite pointless, and the measurable physical properties are what matter. Plasma is a type of fluid, gas and liquid are macro states. Plasma is a macro state where everything is excited, however you find it, it’s never really solid cause of the energy required.
Sharp difference in behavior when it becomes a plasma compared to a gas
To give a bad explanation but a good mental model
Solids – don’t form to their container. Atoms are generally bound together
Liquid – forms to its container. Molecules move past each other freely, semi bound, won’t leave its container
Gas – forms to its container. Molecules move past each other freely. Unbound. Will leave its container
Plasma – doesn’t form to its container exactly, electrons move freely, unbound. Will leave its container
Plasma physicist here.
We all know the distinction between Solid liquid and gas. A plasma is different in that electric and magnetic fields can cause a plasma to move or change. This why the plasma in “plasma balls” move when you put your hand on them. You can also use a very strong magnetic to bend a flame. (Look on YouTube for some examples). It is more complicated than that, but that is the crux of the difference.
This is probably “a man is a featherless biped” explanation, but my understanding is that solids are a fixed shape whereas plasmas are fluids, liquids are not compressible whereas plasmas are, and gasses are invisible where plasmas are not, so it’s kind of like “if a fluid is both visible an compressible, it is a plasma.” I’m sure there are plenty of “*hold up a plucked chicken* behold a man” counter examples to what I said, but in general it should be accurate enough.
The different phases of matter (solid, liquid, gas, & plasma) are differentiated by the internal vibration of their molecules which affects how tightly said molecules hold together.
Imagine matter as a network of atoms held together by chemicsl bonds. When the atoms are in a solid, the chemical bonds act as rigid beams. The individual atoms have almost no freedom of movement as their vibrations don’t have enough energy to overcome the bonds holding them in place. As a liquid, the atons have enough thermal energy to vibrate. Instead of rigid beams, the chemical bonds are acting more like springs. In a gas, the atoms thermal energy has overcome the bonds completely, causing the network to collapse and allowing the atoms to vibrate and move freely. In a plasma, the thermal energy & the associated vibrations are high enough to actually tear apart the atoms’s own internal structures.
Interesting reading the replies here, great question.
“States” are human discriptions of things weve observed and how we describe the world around us.
The ones you’re taught in school are mostly right, but not fundamental descriptions. They are emergent properties of many complex interactions between particles.
Example at the human scale glass is solid. At an atomic scale it is more like a frozen liquid.
Pitch (tar) shatters if you hit it with a hammer, so appears solid, but it drips like a viscous liquid.
At larger scales… A grain is sand is solid. Multiple grains of sand can act like liquids. So is is solid, liquid, liquid like solid? Etc.
These are human made descriptions of the emergent properties we see. They’re still useful to us, but that’s why we can add additional states in to describe weird middle grounds or exceptions to the rule.
I think the word you may be looking for is FLUID. Gasses and liquids are fluids because they flow. Plasma can also.
Imagine gas is like bouncy balls bouncing around, and liquid is like marbles rolling together. Plasma is like those bouncy balls and marbles turning into tiny sparklers that can glow and move with magnets! It’s a special, supercharged version of gas.
Gas, Liquid, Solid: Us electrons and nuclei hang together yo.
Plasma: Electrons are strong and independent, don’t need no nuclei.
Be yeah, as others said, electrons aren’t bound to the nuclei/are still atoms rather than its parts (tho the quarks I believe are still contained in the proton and neutrons).
Gas – atoms are going everywhere and pretty loose.
Liquid – just a bit lose and literally flowing but still in each other vicinity and forming a structure.
Solid – Altogether now, side by side, tightly bound.
Solid, liquid, and gas are made of only atoms. Sometimes those atoms are bound up in molecules (e.g. CO2), sometimes they fly solo (noble gasses), but no matter what, they’re always atoms, with electrons bound up and (mostly) balancing out the charge of each atom’s nucleus.
Plasma is a mixture of bare nuclei and free-flying electrons. This behaves VERY differently from any material made of full atoms.
As a result, although plasma is more similar to gas than it is to any other basic state of matter, it is still its own, distinct thing.
Well, because it’s neither a liquid or a gas. It’s defined by the ions and electrons that make it up, not by how it looks to us