Pendulum Wave Demonstration

This is a large-scale demonstration of the interaction between period and pendulum length, using 16 bowling balls hung from a wooden frame.

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!)

** Who made this? **

** 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. Variable energy loss due to air friction and the striking of the pipe at the bottom (which creates the music) also contribute to differences. Over time, the minor differences become more pronounced.

** Can I get a copy of this video to use in my classroom? **

** How can I make my own? Where can I learn more? **
Here are some links to information about the physics behind this. I don’t have the plans for it, but work through the information at these links and design your own - you’ll learn a lot about physics, math, and construction!

** Where is this? **
It was built on private property in the mountains of North Carolina (United States), near Burnsville. It is not open to the public. However, Jeff Goodman and I recommend some places near this that work to make the magic of the natural world a part of everyday life. The joy and wonder in our world that these places foster is *exactly* what drives the creation of amazing things like this pendulum wave!
AMS is a progressive boarding and day school for 7th, 8th, and 9th graders, located on 100 acres of farm and wilderness. At AMS, students learn to question, evaluate, think creatively and work cooperatively.

***If you've read this far, will you do me a favor?***
Thanks!

[MrPoddu]

The best part of this demonstration is the audio component. There are patterns in the sound, just as there are in the visuals. I know of no other demonstration where you can hear the pendulum "sing" like this. A great touch!

[trevisbest]

This is the sort of stuff Youtube should be for.

[johnnyfreedom]

This is just unbelievably cool! I never would have guessed they would have split apart into a disjointed mess and come back together and do it over and over again! I'd love to hear the science lecture that goes with this! Almost 70, never too old to learn!

[SprigganFR]

This is the kind of creative teaching that can really make an impact on a student. Kudos to this teacher. For me it reminds me of orbital mechanics, and how they can be so chaotic and so synchronized at the same time.

[AmpDecay]

The polyrhythms this creates are absolutely beautiful, music in a pure form  

[iravi]

It's amazing to think how far we have come with science and yet such a simple thing is so mesmerizing and beautiful.

[bunnyfeet]

Simply amazing. This reminds me the importance of experiment and see the real thing working, not just computers simulation

[pablo_ponchito]

That's pretty awesome to see there's so many different patterns in a simple wave...

[jvgifly]

I had seen the Harvard video a couple years back and had to make one. My kids and I used golf balls, PVC pipe for the frame and fishing line. It worked great! A lot of fun. At a couple science fairs the kids would line up to take turns to lie under the pendulum wave as it cycled through
... Good stuff.

[tomshimko]

This is truly incredible.
On a similar note, back when I was in high school (almost 60 years ago), the chemistry teacher had a demo showing water boiling at room temperature. An incredible "aha moment" for me. Became a chemist.

[DaddyZeke]

To correct the lady. The ones on longer strings don't go slower. They actually go the same speed. They just go further since their wave cycle is longer than those on shorter strings. Because their cycle is longer, the period to complete the cycle is longer giving the illusion that they go slower.

[Duben-ymvi]

I. am 73. I never saw this before. Fascinating!

[elizabethscott]

I love the incorporation of sound to the visuals of the wave!❤

[colin_hart]

There are 16 balls total and according to the comments they swing between 50 and 65 times over the whole period until they are synced up again.
Assuming simple pendulum, T=2pi*sqrt(L/g)So the longest one is 1.65x the length of the shortest one. The slowest one (longest) is 1.0404x longer than the second slowest. The second fastest one is 1.03149x longer than the fastest one.The longest one is 8' 4 5/64" (2.5419m)

[lasarack]

10/10

Thank you for all that information in the description! that vote was well deserved

[theurbangentry]

One of the most amazing things I have ever seen.... its breakdown of music theory by the magic of maths and physics really reminds me really how incredible the universe is. Thank you so much for sharing.

[sandradavis]

im not a very science person but this was very interesting and made me want to learn more....loved it

[MrAmazingChris]

And Kids asked their teacher: "Why is this happening, how does it work?" He replied "I have no idea, but this is awesome, right?"

[SmaugDaDragon]

And then the teacher said; "now kids we have the obstacle course ready" - first one through get's a free dinner!

[albertdorio]

I could watch and listen to that for hours on end!