Basic Concepts

I would put "energy" first in the list, even before "force". It is more ubiquitous in physics, in science as a whole, in popular misconceptions of science, and in psuedo-scientific abuse of it. Besides you can have lots of fun defining it at many levels, from elementary Newtonian mechanics where it is just the first integral of Newton's Law, to its definitions in Lagrangian or Hamiltonian mechanics and its connection with time-translation symmetry, its definition in thermodynamics, the E=mc^2 equation, its role in quantum mechanics... all the way to the impossibility of defining it for gravity in GR and its connection to the "problem of time" in quantum gravity, if you dare to go there.

If you don't write this post, I will.

A couple of the obvious ones:

"Energy" especially in contrast to "Power". Not helped by the way the "power company" charges you per energy unit.

Both also have other meanings in other contexts, social, pop psychology, and magical.

"plasma"

"field"

A friend of mine made it much of the way through her first year of graduate school before finally finding out what on earth a "perturbation" actually is.

Delurking now!

I agree with discussing 'energy' as a first topic. Bring open and closed systems into the discussion!

As a non-physicist, I'll welcome all such defining posts.

I do understand a bit of quantum theory, but I sometimes get confused when quantum is used as an adjective, as in quantum gravity or quantum optics.

Velocity. Well, mostly just how it differs from speed, but it's a good thing to get out of the way even if all you need is a perfunctory gesture. Similarly, displacement and distance.

I second the request for energy. I'd also suggest the relationship between thermal energy ("heat") and temperature.

A clear explanation of the nature of "information," as referred to in "information theory" would be helpful, since the terms seems to be popping up fairly regularly, of late.

Great blog, BTW.

Chad,

Always a pleasure to comply. Here's three terms that are pretty basic and could use a nifty definition:

"electric current"
"thermodynamic temperature"
"substance" (as in 'amount of substance')
"luminous intensity"

Here's the link to the SI base and derived units (just to check and see how close one gets).

http://www.physics.nist.gov/cuu/Units/units.html

I'll take a stab at defining "Energy". "Energy": some thing which makes something do something else.

"Ideal": An adjective used to avoid tricky questions related to Mathematica or MCad or PSpice Documentation on physics equations; a term used to depict conditions that don't exist, but which are necessary to cow undergraduate trouble makers.

"Thought Experiment"; an oxymoron used in place of an actual experiment; the rethorical use of Enthymeme to describe scientific concepts in a non-scientific manner.

I'll second the definition of "field". I recently read an article about the Higgs Boson - the part where the author started talking about the Higgs field was confusing. I tried to go back to what I learned about other fields (e.g. the electromagnetic field) but I think I need a refresher on the basic concept.

Maybe not so basic: Heisenberg's Uncertainty Principle is usually stated in terms of position and momentum, but it also holds for energy and time, correct?

Now I'm REALLY a fan of ScienceBlogs. This is a great idea. I bet several basic terms/concepts are already well defined in existing posts. A wiki might be the natural next step.

I'd also suggest some confusion-busting, such as talking about the difference between "force" and "work", "heat" and "temperature", "stress" and "strain", "entropy" and "enthalpy".
Thermodynamics is a particularly misunderstood area, especially amongst ID people. There is a relationship between "entropy" in the thermodynamics sense and "entropy" in the information theory sense (in both cases, it's a measure of the degree to which a frequency histogram is "non-flat"), but it's not true that the second law of thermodynamics applies to information theory. So perhaps a series on basic thermodynamics might be useful.

I'd like to see a clear discussion of voltage in an electrical circuit sense (and it can lead to explaining fields). Of V=IR its definitely the one that I have the hardest time explaining to people.

Another one that I use all of the time and is critical to my conceptual understanding of the world, is continuous vs. discontinuous vs. discrete/quantized. I must use continuum in conversation at least twice a week.

Perhaps a nice discussion of Radiation as well, what it is and why it is just so deadly, could be beneficial. Hmmmm, that'll require a good grounding in the concept of 'orders of magnitude' which is probably something we all take for granted but that most people don't really know how to think about.

Great idea!

Thermodynamics is hard. Microcanonical entropy isn't terribly hard to explain, but beyond that, things can get tricky. When you start throwing in quantum mechanics, it becomes even more of a mess.

A clear explanation of the nature of "information," as referred to in "information theory"

Perhaps SB bloggers should cooperate on some of this. Over on "Good Math, Bad Math" a commenter asked for a clear explanation of information, especially in a physical sense, since he had a math/CS background. He should probably ask here, while wmock could perhaps ask there about the CS information theory sense.

Which goes to my, perhaps not so basic, question about basic information travel.

When discussing why it is impossible for information to travel faster than the vacuum speed of light I get stuck on the new-fangled (for me :-) description that it is the information in the leading edge that is essential for description of signal travel. (From pulse reconstruction experiments.)

How is the essential information in the leading edge of a pulse described? Ie how much of the pulse is needed for a fair reconstruction, how is the group velocity treatment modified, et cetera? An overview of signal travel, perhaps with some words on this, would be interesting.

I think it would be great if you DID NOT follow through with this plan and instead contributed to Wikipedia articles on these fundamental topics. Rather than have every physics blogger describe what "vector" means to him/her, let's have a central repository of well thought out, carefully described popular science articles. The Wikipedia is already an excellent source of science explanations for practicing scientists and laypeople alike; I use the instrument-control PC in the lab to look up something (e.g. "What exactly is that Fresnel reflectivity formula?") almost every day. Interested parties should start by visiting the Wikipedia physics portal at
http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Physics

I think it would be great if you DID NOT follow through with this plan and instead contributed to Wikipedia articles on these fundamental topics. Rather than have every physics blogger describe what "vector" means to him/her, let's have a central repository of well thought out, carefully described popular science articles.

What I have in mind isn't really in the Wikipedia sort of style, and would probably get edited out almost immediately, and I don't want to deal with the hassle. But you can see what you think when I finish faffing about in various comment sections, and actually write the first installment...

(Also, to be blunt about it, nobody's paying me to write stuff on Wikipedia, while I do get a small sum for posting stuff here... I might conceivably recycle blog posts for Wikipedia, but given a straight choice between one or the other, I'll post here.)

Perhaps SB bloggers should cooperate on some of this. Over on "Good Math, Bad Math" a commenter asked for a clear explanation of information, especially in a physical sense, since he had a math/CS background. He should probably ask here, while wmock could perhaps ask there about the CS information theory sense.

Hey, that was me :) I get confused because although I'm familiar with information theory's "information", every time someone tries to explain the physics version of the term to me, it seems kind of more like an intuitive definition, whereas I'm more used to rigorous or axiomatic definitions like are required in the math world. (Torbjörn in the GMBM thread implied there isn't a specific rigorous definition of physical energy, which by itself would explain a lot.)

Chiefly though I would like to third the request for an explanation of the word "field". Lately I keep seeing things where the words "field", "particle", and sometime even "force" are used interchangeably, and I just don't know how to read this. The part about fields and particles being the same thing, or particles "mediating" (???) fields, is what really confuses me the most. (Also, exactly why "symmetry breaking" is important in the context of a field would explain a lot.)

(For the record, I do have to admit, based on my own experience and the comment "beldar" made, that a lot of the physics newbies these days having trouble with the word "field", the main reason we're asking in the first place is we're having a lot of trouble understanding what the Higgs Boson is and what it does.)

Lastly, on the "you people should just write wikipedia articles" thing, I would like to vote no no no no no. First off, I don't know about anyone else, but for all the things I ask about above, I've already read the wikipedia articles and just walked away confused. Second off, when I see stuff explained on scienceblogs, the main reason I find it easy to understand is because it tends to be written in sort of an informal conversational sort of style written with a particular audience in mind, very unlike the ultra-dry writing one finds on wikipedia. Explanations of the kind we would be likely to see in this scienceblogs mini-project wouldn't be accepted on wikipedia or would be edited to pieces until what made them accessible in the first place was no longer present-- which is as it should be, since the intent of wikipedia is to write pure reference material and the audience is different.

The main point is about duplication of effort. If there are perfectly good explanations of "vector" and "skyrmion" and "elementary excitation" on the web, why write a new one? The charm of your blog is seeing what physics and physics teaching look like from the perspective of a junior faculty member. No one wants you to regurgitate textbook material on-line. Elegant essays like Jennifer Ouellette's about (for example) foam in science, art, literature, popular song and alcoholic beverages are another matter all together, but that doesn't seem to be your style either.

A suggestion made is to make these posts linkable as an FAQ.

I get confused because although I'm familiar with information theory's "information",

I'm sorry; I didn't mean to suggest you were confused, nor do I think you are. After all, where should you shore up any information (hep!) if not by asking?

I was trying to point out some difficulties for SB posters (and readers!) in answering cross-disciplinary questions.

Torbjörn in the GMBM thread implied there isn't a specific rigorous definition of physical energy,

Well, more exactly we were discussing information and different measures (physical and informational) of entropy.

Definitely "field".