"Classic" Timekeeping, Part II

(Part I)

The state-of-the-art timekeeping technology a century ago was comprised of pendulum clocks. Refinements were made in the areas of obvious problems, such as the mechanical escapement which robs the system of energy, the vulnerability to changes in length from temperature and humidity, and vibrations. The culmination of this was the clock of W. H. Shortt, which had two pendulums, a master and a slave. The master oscillator was a free pendulum, and as it did no work to drive any mechanism, it was able to keep very precise time. The pendulum was made of invar, a material that had a very low thermal coefficient of expansion, and was encased in a chamber that was evacuated to several millitorr of pressure. The chamber was bolted to a wall that typically rested on a massive platform of the type used for telescopes, which minimized effects from vibrations. The pendulum was given an occasional boost to keep its amplitude roughly constant. The slave pendulum, which did the mechanical work of the system, received periodic electronic impulses from the master clock to correct its motion. This type of clock could keep time to better than a millisecond a day. A shortcoming (as it were) was in the measurement of the time; as Loomis notes

This remarkable result is accomplished through the possibility of averaging a large number of observations. A single impulse from a master Shortt clock has an uncertainty of 1 or 2 milli-seeonds. The master pendulum carries a small wheel. The impulse arm rests on this wheel, and as the pendulum swings out the pallet on this arm travels down the edge of the wheel, finally falling clear . It then trips an arm which falls, making the electric contact . If the small wheel is not exactly circular the arm will fall at slightly different times as the wheel is given a small turn with each fall. These variations are entirely smoothed out when a series of sparks are averaged.

So while the clock is precise in the long-term, the system of measuring it (described below) is limited at shorter durations.

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Extra Credit

“Secret” Physics they don’t teach you in class —

The Fifth Law of Thermodynamics: Beer is good.

The Sixth Law of Thermodynamics: Men driving sports cars are assholes.


On the vagaries of random playlists on the iPod:

The transition from Bobby Darin’s “Mack the Knife” to RHCP’s “Funky Monks” at oh-dark-thirty in the morning, before caffeine and not really fully awake, is a little harsh.

I’m just sayin’

Don't Sleep Through This

Giving a Good Talk over at Life as a Physicist.

Unfortunately (or fortunately) there is a lot more to giving a good talk than just a good deck of slides. I think the number one thing for me is “tell a story.”

Some good tips to check out. A couple to add:

Don’t make your graphs too complicated and the admonition of death-before-yellow-on-white applies here as well. Also remember that (red/green) color blindness is not all that uncommon, so — especially if you’ve used red and/or green — point out which line you’re discussing, rather than just saying “the red line represents X”

I’ve heard a common critique that the presentation slides should be cartoonish, but I rarely find them funny, so I use a different description — simplify. The text should be the highlights, not a transcript. If you’ve followed the advice about fonts (I say minimum size ~18), you won’t be able to fit everything you say on the slides, anyway. You shouldn’t be speeding along any faster than about one slide per minute. And remember to breathe.

The Physics of a Half-Gaynor

Physics Floundering saved by Disco Parody

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And just like that when I had given up all hope,
I said nope, there’s just one way to find that slope.
And so now I, I will derive.
Find the derivative of x position with respect to time.
It’s as easy as can be, just have to take dx/dt.
I will derive, I will derive. Hey, hey!

via Talk Like a Physicist

Dissin' the C-Monster

C is for Carbon, parts 1 and 2, over at Cocktail Party Physics

An interview with Eric Roston, author of The Carbon Age: How Life’s Core Element Has Become Civilization’s Greatest Threats

C is for cookie. That’s good enough for me.