Poll: Most Important Part of Physics?

Originally I was going to go with "Momentum," on the grounds that it's something a person can easily see, not to mention check and confirm experimentally, and can therefore be a basic stepping stone.

But, considering my options, I realized that thermodynamics has a similar basic quality to it, with the added benefit of beginning to discuss some important limiting concepts (namely, entropy).

Emmy agrees with me that Condensed Matter is tastier than any of the other options. In any case, to understand Condensed Matter one has to understand all the rest, except GR (except if you happen to be looking at astrophysics near a black hole). And also, there are far too few popular books on Condensed Matter, one more on most of the other topics in your poll would hardly be noticed. "Condensed Matter for Dogs: food for thought" is probably too silly for a title, and anyway soft materials are much harder than crystals, etc.

As a mechanical engineer, I might be a bit biased, but I think an understanding of energy (and mechanics, and probably thermodynamics) is key to understanding our everyday world, and that's what is important to the general public.

Scaling laws and units.

If there were one area of physics I wish everyone left high school knowing, it is why a 2x4 supports more turned on edge than flat, that doubling the linear dimension of a rain barrel increases its volume by 8, that pulling one pound for ten feet is the same amount of work as pulling ten pounds for one foot, and that using block and tackle doesn't change the amount of work required.

Yeah, I know, this is simple stuff. And it's stuff that most people don't know.

Vectors would be nice, too.

Energy is a subset of classical thermodynamics, but there is more to thermodynamics than energy that is important. Namely, that there is no free ride, so the best you can do is break even (which is only possible in idealized limits).

It is hard to pick just one, though.

To me the most important part of physics: is its way of thinking, its way of seeing, interpreting and explaining our world.

Electromagnetism. Because: Magnets, how do they work?

In the order of importance:
1. Newtonian mechanics
2. Classical electromagnetism, especially basics of electrical circuits
3. Thermodynamics

I agree with Greg at #6. Whatever topic(s) in physics are best for accomplishing this goal is the most important part, and I am not a physicist and don't teach physics, so I don't know what those are.

Orbital Mechanics. Perhaps I lack ambition, but I'd settle for getting the general public out of the dark ages.

I'd go with Units too. In HS I think the most impact (and lifetime useful) input I got were from a book "Mass, Length, and Time" coupled with learning how to use a slide rule. I'd closely follow these with some Newtonian Mechanics, then Thermodynamics. There really is no one topic (in the classical compartmented sense) that grounds all others.

And to illustrate the comment "most people don't know them", I once went into a Lumber Yard to get some 2x1 wood for a project. The (very polite and helpful) young lad who was helping me frowned and said "hmm, 2 by 1 - I don't think we have any of those". Shortly followed by a bright "Ah, but we do have some 1 by 2. Will they do instead?". I kid you not.

Classical Mechanics

It is important, I think, that the general public becomes familiar with the distinction between

- what any particular experiment can check; namely: hypotheses or expectations of certain result values, as may be summarized by various "models", and

- what not; such as the particular method of how to derive a result value from observations collected in any one experimental trial, which derives from the systematic (a.k.a. "theoretical") definition of the particular quantity to be evaluated.

As illustration of this important distinction (and as far as it is not listed above as a physics topic itself) I'd pick covering the theory of relativity; drawing the described distinction for instance to covering particular models of cosmology, or astrophysics, or astronomy, or geography, or chemistry, or of nuclear physics. And for starters surely the special theory, rather than the general one.

I would have voted ballistics, but that's probably to applied for the pure.

Digital electronics (look around you).

Well, ok this is a pretty big basket, with loads of formal logic, computer science, materials science, quantum and more, but ever explain to your nearest and dearest why the lk4&*^&*($#$ whatever ain't doing what it should.