19th Century Physics for $400, Alex

What are Maxwell’s Equations?

At first glance it’s pretty good, although there are one or two things I think aren’t expressed well. One is the divergence of E equation. It’s written as being equal to zero, with the explanation that this is true when there are no charges arund. Well, the other form that’s discussed,

\(\nabla\cdot{\bf E} = \rho/\epsilon_{\tiny 0}\)

is always true. If there are no charges around, rho is zero. I’m not a big fan of equations that are written for specific cases. The first thing that happens is you forget the assumptions and caveats, and then when you try to apply it in general, it fails to work. Use the general equation and then apply the boundary conditions. You’ll be better off in the long run.

Then there is this canard:

Longer wavelengths include heat (infra-red waves)

No! Heat is NOT a part of the EM spectrum. It’s true that for room-temperature items and thereabouts, the bulk of the energy radiated is in the infrared part of the spectrum, but not all IR is from thermal sources, so equating the two is wrong. Furthermore, when you get hotter, you start getting visible light. Like from a stove burner or the sun — all of that light we can see? It’s still radiant heat!

I Don't Like Mondays

Today was a Very Bad Day™, in a depressingly long and growing list of Very Bad Days™. And while there are bound to be proclamations of “it’s too soon to talk about the implications” countered by “if not not now, when?” and so forth, and also some shooter(s) was/were (religion) and (ethnicity) and this has profound implications because of (generalization and/or inappropriate extrapolation), that discussion really doesn’t interest me right now, because we don’t know everything yet.

Of more immediate import to me is the one certain fact: that we don’t know everything yet. That was true all day, as the stories poured out — they were sketchy and often wrong. One shooter, two shooters, three shooters — the number kept changing. One shooter was down, and then that was withdrawn, and then confirmed, but nobody could say if “down” meant dead or arrested. Shooting at Bolling AFB was reported, and then dismissed as being false.

Information dissemination is fast. Twitter and internet news were reporting this very soon after it started. Information collection is slow, and since it’s also imperfect it requires confirmation, making it even slower. And this is one things that tends to get glossed over in the aftermath. That while all of this was going on, we didn’t really know what was happening. It was true after the Boston Marathon bombing and manhunt, and it was true in all of the other incidents before that. If you are going to get involved in any sort of discussion, don’t fall prey to the notion that anyone had more than scant knowledge, or that anything about this should have been obvious. That’s hindsight bias.

(one note, since you may not be familiar with DC at all: I don’t work at the navy yard. Emotions aside, in the grand scheme of things this event only had a minor impact on my day, in that we were in a heightened security situation)

My Apologies

The site has been flaky, especially of late. I understand pages will not always load, and it’s been a problem loading the admin pages as well. There have been occasions where I could not write or post anything because everything was acting up during my window of time where I was trying to blog. I’m not sure what the fix is, or when it might happen.

So, in the words of mad prince Ludwig, many apologies for the inconwenience.

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I Kick a Touchdown

Wide Left: Study Shows that Holders Play Key Role in Field Goal Accuracy

Using the model, the researchers found that if the ball is leaning to the left or right, it will affect the trajectory of the football. And the more it leans, the more pronounced the effect, which is the result of complex interactions between the rotational motion and aerodynamic forces acting on the football.

“For example,” Mazzoleni says, “if the ball is tilted 20 degrees to the left for a 45 yard field goal attempt, it will sail up to 3.5 feet to the left before hooking back to the right.” And any football fan can tell you that 3.5 feet can be the difference between winning and losing. (Just ask the University of Nebraska.)

The paper’s abstract indicates they checked with real results

A case study was performed for which experimental data were available, showing the trends of the flight of the ball captured in our simulations in actual game situations.

The title is a quote attributed to Garo Yepremian, a pretty good kicker who played for several teams from ’66 to’81, including the ’72 Dolphins. Sorry, Garo, the holder is blameless for that horrible decision to try and pass the ball in Super Bowl VII.