Board President
Pendulum Wave Demonstration
by Board President - Tuesday, 9 September 2014, 10:07 PM

September 2, 2014 

Got to see this demonstration of physics by bowling balls this weekend. It's beautiful and cool. Watch all the way to the end to see the balls move back in phase with each other, as they are at the start. In between, it moves from beautifully ordered to apparent chaos and back, again and again.

A viewer noted that if you scroll through the video, the green ball hardly moves. I assume that the sampling rate of the video for the scroll on Facebook is almost (but not quite) the same as a multiple of the period of that ball's oscillation -- a happy accident. It's quite cool and worth trying to see. This worked for me on mobile, but not on the computer. 

Because this video has been very popular, here are answers to some common questions:

** What am I seeing? How does this work? ** 
The length of time it takes a ball to swing back and forth one time to return to its starting position is dependent on the length of the pendulum, not the mass of the ball. A longer pendulum will take longer to complete one cycle than a shorter pendulum. The lengths of the pendula in this demonstration are all different and were calculated so that in about 2:40, the balls all return to the same position at the same time – in that 2:40, the longest pendulum (in front) will oscillate (or go back and forth) 50 times, the next will oscillate 51 times, and on to the last of the 16 pendula which will oscillate 65 times. Try counting how many times the ball in front swings back and forth in the time it takes the balls to line up again, and then count how many times the ball in back swings back and forth in the same time (though it's much harder to keep your eye on the ball in back!).

** Why are they not perfect at the end? ** 
This large frame is built from wood and is outdoors, which means it expands, contracts, and flexes. Because the position of the frame changes, the cycle lengths are not perfectly aligned. Over time, the minor differences become more pronounced.

** Where is this? ** 
This was built on private property in the mountains of North Carolina (United States), near Burnsville. It is not open to the public.
However, I can recommend two places near this that work to make the magic of the natural world and art a part of everyday life. The joy and wonder in the world that these places foster is *exactly* what drives the creation of amazing things like this pendulum wave!
--> For all the kids in your life, check out Camp Celo:
This is a farm-home camp for kids 7-12 (and older kids can work there!). I can’t say enough great stuff about this camp. It’s a wonderful place for kids to experience independence and joy and simple pleasures. No cell phones or tv, just home-grown entertainment like this. If you don’t have kids to send there, please make a donation to nonprofit Friends of Camp Celo ( to help send a child to camp who otherwise wouldn’t be able to go. I am on the Board of this all-volunteer nonprofit and can attest to the great work they do! (In fact, this video was taken at one of their events.)
--> For adults, check out Penland School of Crafts:
This is a craft school where you spend 1-2 weeks or longer working intensively in one studio. Get hundreds of artists together and magic always happens! Penland has a giant walk-in pinhole camera and other cool demonstrations of the magic of science and the everyday world. You don’t need to be an artist to attend!

** Can I get a copy of this video to use in my classroom? ** 
You are encouraged to use this video for educational purposes! If you are sharing online, please provide a link back to this video or the YouTube video. This video is licensed CC BY-SA:

** How can I make my own? Where can I learn more? ** 
Here are some links to information about the physics behind this demonstration. There are some small scale versions of this demonstration that can be purchased commercially as well, but if you want a 20’ version like this, you’ll have to make your own! I didn't make this and I don’t have plans for it, but work through the physics at these links and design your own – you’ll learn a lot about physics, math, and construction!

***If you've read this far, will you do me a favor?***
Go to this link and vote for JJ to be the 2014 American Hero Dog:
JJ is a very special little dog who protects a very special little girl named KK's life by doing something just as magical as what you see in this video: JJ uses her nose to detect when KK is having a potentially life-threatening reaction, before any medical equipment can detect it. It's hard to believe, but it's absolutely real. I've seen it myself many, many times -- but what's more important is that her doctors have seen it, and they were so convinced that JJ was better than their monitors that they invited her into surgery at Duke Medical Center last December! You can learn more about JJ at But please vote! The contest ends on September 15th and you can vote every day until then. If you like KK’s and JJ's page, you can get a picture and reminder every day:
Thank you!
 — at on private property near Burnsville, NC.