Archive for December, 2011

2011: The Top 10, in Base 14

Greatest posts/year-in-review lists seem to be all the rage, so why not?


The top traffic posts that are not simply one of my many links, i.e. there is significant commentary or it’s an original piece. Not always about physics or technology.

MiniMe, You Retweet Me

Blogging: You’re Doing it Wrong! (Part 1) (and others in the series)

Here Be Dragons

Time for a New Article on Time

Have You Checked the Woodworking Lately?

Thou Shalt Not Dilate Thy Time


Other physicis-y post highlights for the year

There Must Be Room for Debate

Poolside Optics

The Butler’s Name is Emissivity

Today is Fara Day

Photography and Physics Tutorial: Filtering and Polarized Light

You Can’t Even Hope to Contain Him

The Nose Knows Physics


And one non-physics highlight:

If I Did It

Look Ma, No Calculator!

Mental Math with Tricks & Shortcuts

I don’t think I could memorize more than a few beyond what I already know.

Is it Time for the Hanke-Henry?

Is It Time to Overhaul the Calendar?

Their proposed calendar overhaul — largely unprecedented in the 430 years since Pope Gregory XIII instituted the Gregorian calendar we still use today — would divvy out months and weeks so that every calendar date would always fall on the same day of the week. Christmas, for example, would forever come on a Sunday.

“The calendar I’m advocating isn’t nearly as accurate” as the Gregorian calendar, said Richard Henry, an astrophysicist at Johns Hopkins who has been pushing for calendar reform for years. “But it’s far more convenient.”

In keeping with Betteridge’s law, I think the answer is “no”. The objections noted at the end are enough, but inertia is probably enough. The US can’t even get the metric system in place, and there’s a strong passive-aggressive streak of opposing changes that the government tries to instigate. This is also something that a majority of the world would have to adopt, in order to force everyone to do so. I think you need more than streamlining calendar printing/software.

Why there is Line of Sight, and not Line of Sound

Everyday Science: Why Can You Hear Around Corners But Not See?

[W]e’ll start with a question: why can I hear my cats around the corner, but not see them?

Pretty Much Blind and Deaf

Abstruse Goose: The Sliver of Perception

Look at Me

You need to a flashplayer enabled browser to view this YouTube video

Time lapse: The spectacle of Comet Lovejoy

Invisible Numbers

I’ve posted before on how liquid-crystal display (LCD) monitors emit polarized light (and can be birefringent), and some of the fun you can have with this, and everyone is probably familiar with other uses as well.

LCD’s don’t emit light by themselves; they rely on backlighting or on reflecting ambient light, which passes through a polarizer behind the display. In this short video we can see what happens with a calculator display when you take the top polarizer off:

You need to a flashplayer enabled browser to view this YouTube video

We see nothing at all. The effect of the display is not visible to us, because we are not (very) sensitive to polarized light. When we put the polarizing screen in place, then we can see what’s happening — the display has a “zero” energized, which has a different polarization than the rest of the display and blocks the light that has passed through the display and been reflected and polarized. When we rotate the screen, the light is blocked from the rest of the display, and the light from the zero passes through. At an angle, light of each polarization makes it through, so you can’t see the digit at about 45º.

Make Your Geekdom Saving Throw

How to make your own Dungeons & Dragons chocolate dice mold

Violating Betteridge’s Law

Does a Magnet Gun Conserve Momentum?

Betteridge’s Law of Headlines: “Any headline which ends in a question mark can be answered by the word ‘no’”. But this is a physics topic, and conservation of momentum is a pretty well-established law if there is no net external force on the system. So we expect the answer to be “yes”. Thus you can tell Rhett is not a headline-writer looking to stir up controversy, else he would have written something like Does a Magnet Gun Violate Conservation of Momentum?

You need to a flashplayer enabled browser to view this YouTube video

Looks like a fun toy, and I’m a sucker for fun toys. To the bat cave lab!

Burning for You

Christmas with Faraday: The Chemical History of a Candle

Faraday gave a series of famous Christmas lectures each year at the Royal Institution — a tradition that continues today. One of the earliest, on the chemistry and physics of flames, became a popular book: The Chemical History of a Candle.

These lectures were a gift that Faraday gave year after year to those who showed up to receive it: the gift of wonder at the natural world that continues to surprise us, even today, with its mysterious workings.


What is it like to have an understanding of very advanced mathematics?

You can answer many seemingly difficult questions quickly. But you are not very impressed by what can look like magic, because you know the trick. The trick is that your brain can quickly decide if question is answerable by one of a small number of powerful general purpose “machines” (e.g. continuity arguments, combinatorial arguments, correspondence between geometric and algebraic objects, linear algebra, compactness arguments that reduce the infinite to the finite, dynamical systems, etc.).

One of a long list.

It’s hard to convince those that don’t “speak” math how necessary it is, rather than being forced to explain things in a much less precise language (be it English or something else) that the audience understands.

via @seanmcarroll

The Nose Knows Physics

@neiltyson tweeted

According to the song, Rudolph’s nose is shiny, which means it reflects rather than emits light. Useless for navigating fog.

To which I responded

Nose also glows & bright. Since it’s red we could determine temperature if a thermal source & estimate Rudolph’s calorie needs

If Rudolph’s nose is a thermal source it will follow the Stefan-Boltzmann power law, which tells us the radiated power depends on the fourth power of temperature. Something red-hot will have a temperature of about 1000 K. Now this is an estimate and since it’s raised to the fourth power, will give us a large error bar on our answer. But let’s go with that because I don’t have a calculator handy. For the emitted power we multiply by the area, a few square centimeters (converted to square meters) and Stefan’s constant. Assuming I did the math correctly, we get about 10 Watts. The temperature should not be as large as 2000 K, which would give us and answer 16 times as large. (I am ignoring the “power absorbed” term in the equation, because at these temperatures it’s going to be small — 300K or less)

There’s also the emissivity. The nose is shiny, meaning the emissivity is not close to 1. So perhaps we double our guesstimate. Tens of Watts, maybe as large as 100 Watts as a probable value.

A thermal source has a maximum luminous efficacy of 95 lumens/Watt, at a temperature of around 6600 K but actual bulb filaments that give us white(ish) light are a lot closer to 10 lumens/Watt. So the nose probably emits around 1000 lumens at best — this is not even as bright as a traditional 100W light bulb, but is around what low-beam halogen headlights emit. However, those have reflectors on them to direct most of the light into a beam. Rudolph’s nose emits into a much larger area.

So perhaps the nose is not a thermal source (unless it’s much larger than I estimated) — the radiation is not because it is hot. We could check this if we knew the spectrum of the light being emitted. Perhaps it is some other type — does Rudolph have an LED nose?

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