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## Simple Pendulum Experiment Showcases Beautiful Wave Forms [Video]

This physics demonstration combines pendulums with different lengths (but all swung at the same time) to highlight different wave forms and how they fall in and out of harmony.

The group behind the video, Natural Science Demonstrations, explains:

Fifteen uncoupled simple pendulums of monotonically increasing lengths dance together to produce visual traveling waves, standing waves, beating, and (seemingly) random motion.

The period of one complete cycle of the dance is 60 seconds. The length of the longest pendulum has been adjusted so that it executes 51 oscillations in this 60 second period. The length of each successive shorter pendulum is carefully adjusted so that it executes one additional oscillation in this period. Thus, the 15th pendulum (shortest) undergoes 65 oscillations.

Our apparatus was built from a design published by Richard Berg [Am J Phys 59(2), 186-187 (1991)] at the University of Maryland. The particular apparatus shown here was built by our own Nils Sorensen.

Jason Fitzpatrick is warranty-voiding DIYer and all around geek. When he's not documenting mods and hacks he's doing his best to make sure a generation of college students graduate knowing they should put their pants on one leg at a time and go on to greatness, just like Bruce Dickinson. You can follow him on if you'd like.

• Published 04/20/12

### Comments (8)

1. miki

WOW!!

2. MJ

Really nice, thanks for posting this!

3. cadkins

you are getting sleepy……when I count to 3 you will awake and remember nothing…one…two….thr….

4. r

…uhhh?… for some reason the only thing I can remember is…nothing.

5. Paul

And they say God doesn’t exist. All this beauty just happens by “accident”. Right.

6. StevenTorrey

Fascinating. The regularity of the motion is what is so fascinating. Regrettably, they did not include the weight of the balls, the length of the individual strings or what the balls are made of. Would there be different results with different weights, or balls made of some other material? Even going to the WebPage–Harvard–fails to include this basic info. It would also be helpful for the viewer to point out that the video is unedited, people being suspicious of manipulation. But still fascinating.

7. Ignacio Curiel

I agree with StevenTorrey above, and I would LOVE to build my own pendulum set. Is there a chance to get the information needed? Thanks!!

8. Doug

I haven’t seen a physics book for 50 years, but I believe that the period of a pendulum is determined by its length and the weight of the item at the end of the shaft (string). You could use anything at the end of the shaft, but the key is to adjust the weight or the length of the shaft so that the longest pendulum has a period of 51 cycles in 60 seconds. If you don’t care to duplicate their results exactly, you probably don’t have be that close, but each shorter pendulum has to make one more cycle over 60 seconds.
For starters, pick a weight. It has to be one that you can get several of (maybe a sinker for fishing) and a length of string. Give it a swing and see what you have. If you don’t get enough cycles per 60 seconds, shorten the string, or use a lighter weight. The first pendulum you make, sizes the whole aparatus.
The weight has to be humg on a string that is v-shaped to keep it oscilating in only one plane; it forms something like a hinge. It sounds like a fun project, but knowing my track record for completing things, I’ll stick to sharing the video.

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