Today I am heading off to speak at the Essential Magic Conference – if you are into magic, check out their site and register for the best value magic event in the world!

I have posted something similar to this next video before, but I love this simple but powerful UV version….

Anyone want to have a go at explaining it?  Are the strings a special length?

## 15 comments

1. The patterns that we perceive are just that – a perception. Our brains look for patterns, so when they occur we recognise them very quickly. The patterns that arise are an emergent property of the interactions of pendulums with frequencies offset by a standardised amount – which is determined by string length. Cool effect!

2. Justin says:

The period of a pendulum is roughly proportional to the square root of the length, so the shorter the string, the more swings it makes in a minute. The difference in the number of swings between the shortest and longest isn’t that great, so I’m guessing it was set up so that over 1 minute, each pendulumn would have one less swing than the one before it. As they swung, they would gradually get in and out of phase with each other.

3. It’s simple physics. The period of a simple pendulum is, for small amplitudes, proportional to the square root of the distance of the bob weight from the suspension point (at least to a decent approximation).

It’s therefore “just” necessary to adjust the relative lengths of the individual strings to obtain the effect seen. The “just” probably meaning lots and lots of small changes. It looks like the progression of the suspension lengths is linear with distance from the camera, so the relative periods of each successive bob will be a fixed proportion of that of the one before it. If you make that proportion such that (say) then 9th bob has half the period of the first, then you would get nice effects.

I guess many other patterns are possible, although the requirement to keep the bobs in an aesthetically pleasing perspective will limit that.

4. Greg says:

Next time you sit at traffic lights, look across at the line of cars waiting to turn right. See if you can keep your eyes on 3 car’s indicators. No matter what the rate at which they blink you’ll see them exhibit all sorts of wave phenomena – synchronicity, beats, discordance…

After you’ve seen it once, you’ll never be able to unsee it.

5. Ian says:

That’s a beautiful and mesmeric effect and, yep, simple physics and pattern recognition; or magic: it could be magic! Tiny light elves and Maxwell’s demon ensuring an even distribution of energy 😀 Either way, I like it 🙂

6. The video isn’t helped by the “Don’t forget to rate…” and “Click here to be notified…” pop-ups.

7. Moray says:

Lovely!

I did a project looking at similar (ish) stuff using guitar strings, weights, a big magnet, a frequency generator and an oscilloscope

8. Anonymous says:

Short pendulum swings faster than long pendulum! Amazing!! Stupendous!!!!
No, trivial.

9. I started picking apart simple harmonic motion, but we don’t need that. Just the square root rule mentioned above. I don’t suppose this blog supports Latex, so in what follows, I’ve put ni for n sub i etc.

The pendulum swings coincide at one point. Let ni be the number of swings done by pendulum i at this point. Let Ti be the period (time taken to make a complete swing) by pendulum i. Then the number of seconds that have elapsed is ni times Ti.. So at this point
niTi = njTj for every i and j.. Since the period is proportional to sqrt(L), where L = length of string.we have

(ni/nj)^2 = Lj/Li

Let n1, n2, … n12 be a sequence of increasing integers. Say nj = j times n1. Then Li/Lj = j^2/i^2. Yes! Let L12 be the length of the shortest string. Then

L11 = 12^2/11^2 time L12 = 1.19 times L12.

and Lj = 144 / j^2 for the rest of the j’s.

Pendulum 1 makes n1 swing, pendulum 2 makes 2 x n1 swings etc before they coincide, In there intervening time they make pretty patterns.

Does this support Latex? $n_i$. \$n_i\$

10. Tony Terry says:

Gotta love Barton’s Pendulum!

11. One Eyed Jack says:

The black light adds to the effect, but it’s not my favorite.

Look at fractals for some truly fascinating patterns that emerge from surprisingly simple systems.

12. Quite trivial physics. I would have expected Mr. Weisman to know this.

13. Do you want to have a go at explaining your question “Anyone want to have a go at explaining it?” ? What do you want us to “explain”?

14. This is mesmerizing to watch–all three versions! It’s such a simple thing, and yet so very cool to see the gradual change from one pattern to the next.

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