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Krulwich Wonders: A Pendulum Dance

Thursday, May 19, 2011 - 02:00 PM

Harvard Natural Sciences Lecture Demonstrations/YouTube Harvard Natural Sciences Lecture Demonstrations/YouTube (NatSciDemos/Youtube)

The following post is from Robert's excellent blog Krulwich Wonders. You can read all the articles from Krulwich Wonders here.

Cinderella's Ball, This Time With Pendulums

What we have here is better, more cunning and a damn sight more beautiful than magic. It's a pendulum dance.

A team at Harvard built this device. It's got 15 free-swinging pendulums, each a different length.

The longest one does 51 swings a minute.

Its neighbor, a little shorter, does 52 swings...the next, 53, then 54 and so on...

The little guy down at the end does 65 swings a minute...

Once they're set swinging, the balls form a line, then quickly fall out of sync and, as you watch, patterns emerge out of nowhere, snakes, squiggles, spirals. At the exact midpoint (57 seconds in on the video), half the pendulums are at one "amplitude maximum," the other half at the other "amplitude maximum," like ladies and gentlemen at a palace ball. You can almost see them curtsying and bowing.

But here's the sly part.

There are secret choreographers in the house: Time and Motion. The Harvard design team has built the device so the pattern repeats every 60 seconds. Precisely. This dance, like Cinderella's ball, has a fixed end point.

You can see this yourself by sliding your cursor to the 27-second mark on this video when the pendulums are released (I want to say pendulii, but spell check keeps shouting "no!"). At 1:27, exactly a minute later, all the balls are right back where they started. Exactly. Same formation. And then the dance repeats. Very cool.

Harvard Natural Sciences Lecture Demonstrations Source: YouTube

The joyful team that did this (I shouldn't be squealing, because they'll be swamped with wanna-be interns) call themselves the Natural Science Lecture Demonstration team. They supply Harvard professors with razzle-dazzle show & tell machines to use in their science classes. That's really what they do.

Wolfgang Rueckner, one of the four full-time "managers," told the Harvard Crimson: "We have close to a thousand demos," some of which you can see here.

Most are simple constructions, things that ordinary folks could do at home. Mr. Rueckner has an ordinary PhD in atomic and molecular physics.

But while he may be a pretty smart guy, he's designing for the heart first, then the head. "We hope to add to the educational experience and make these scientific concepts more understandable," Rueckner says. "We're doing it visually and experimentally, hopefully with a little flair, and humor and showmanship so that it can be remembered."

I'm definitely remembering this. I might even (I'm not saying I will, I'm just saying I might) try to figure out the physics that makes it happen.

For those of you who are now intrigued, the Harvard site is chock full of ohmygod! videos, including one where a guy named Allen is placed on a bed of nails, covered with another bed of nails and someone then pounds on this nail sandwich with a huge sledge. Geez. The question posed is why isn't Allen in pain? Good question. Especially when we watch Allen get up, dust himself off and say, "That was fun."


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Comments [10]

Crystal Balla


Mar. 27 2014 04:24 AM
Chelsea Cartwright from Weed, CA

Hi Robert,
My name is Chelsea Cartwright and I work at College of the Siskiyous for the science department in Northern California. I'm writing you because we are moving into a new science building and in desperate need of artwork for the walls. I love this snake pendulum photo and am wondering if you might want to sell it. We are looking for high resolution, non-JPEG format photography. Please let me know via e-mail at
P.S. I love RadioLab!! Listen to it every night.

Jan. 31 2012 03:43 PM
Truth from Manhattan

I contribute to both RL and This American Life. And RL gets contributions from, NPR, AP Sloan, etc..

Do people have a right to complain, whether they contribute or not? Of course. It lets the RL decision makers know what their viewing audience is thinking. The only bad info is the critical info that never makes it to the decision makers and information ignored.

My personal feeling is RL started off so well, it's getting hard for them to match or top themselves.

I think everyone who's complaining and not contributing, should contribute. I those that are not complaining but not contributing should contribute. And freedom of expression, even if we don't like it, should continue. That is the premise of the show - science: purely objective.

May. 24 2011 01:29 AM
Steven from Palo Alto, CA

As a first-year middle school math teacher, I have been extremely busy and have not listened to Radiolab as regularly as I used to. When I came to the site this weekend to find a clip from the Stochasticity episode as an intro to my last unit of the school year on probability I unexpectedly came across this video, which reminded me why I ever got into Radiolab in the first place. The big, lofty ideas that Jad and Robert tackle on full length episodes are always captivating and thought-provoking. Yet a short, silent clip like this one fills my mind with awe, wonder, and appreciation for math and science; the same feeling that inspired me to pursue math and then to become a teacher. Thanks, Robert, for reminding me that math is fun! (I will remind my students, as well.)

This video falls along similar lines and is definitely worth checking out:

May. 24 2011 01:05 AM

This was cool!

If someone isn't contributing money they have no right to complain about the length or content. It's like the people who don't vote and complain about what the state and federal governments are doing.

May. 23 2011 02:13 PM
mark from bay village, ohio

people who are complaining about the number of shorts radiolab puts out and the "suffering quality" (which it is not) should stop complaining and start donating more money. it's not like this is some network TV show that makes millions on advertising and has enough staff to have a new show every week.

also, just because they don't lay it out for you as to what the "meaning" of this pendulum thing is doesn't mean you can't search for why this would be applicable to your every day life. use your imagination.

May. 23 2011 11:56 AM
MoreFullLenghtShowsPlease from Manhattan

I agree with Rich from Billerica, MA. I find I come to RL less frequently because I'm more often than not disappointed with the offerings of lackluster shorts. Are you changing the format to shorts only? The longer stories not only were longer individually, but often took up several episodes; they really took things apart.

Don't get me wrong, wave pendulums are fun and interesting to watch, but this isn't cutting edge, and besides showing someone else's beautiful video it fails to talk about applicable science and societal ramifications. You'd have been better off talking about fractals and different societies use of the, and started by showing iTunes fractals. Sadly, it just wasn't intellectually engaging. Sorry, I'm I just failing to see your overall strategy, if so, let me in on it.

I'm a big fan too, but you need to step it up.

May. 23 2011 08:47 AM

stunning and absolutely mesmerizing

May. 22 2011 12:46 PM
Andrew Thomas from brooklyn

its surely no coincidence that they picked fifteen balls (a full scale of half steps in music, octaves included...) is there a corollation?

or if there isn't, could you create the mechanism so that the first had a period half of the last? wouldn't this replicate visually, the dissonance that you hear on a keyboard when you press all the keys at once? then you could just 'play' selective pendulums, and look at what a minor seventh chord sounds like for example...

would love to see it :)

May. 21 2011 10:42 AM
rich from billerica, ma

you guys do a great show. told friends about RL and text donations. but lately only shorts.

wish you would produce more material.

expecially neuro science.

a fan


May. 20 2011 11:38 PM

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