# Cool videos of dynamics

I just discovered the Harvard Natural Sciences Lecture Demonstrations – a catalog of ways to learn and play with science. It’s all fun, but a few of the videos provide nice demonstrations of dynamic phenomena.

Here’s a pretty array of pendulums of different lengths and therefore different natural frequencies:

This is a nice demonstration of how structure (length) causes behavior (period of oscillation). You can also see a variety of interesting behavior patterns, like beats, as the oscillations move in and out of phase with one another.

Synchronized metronomes:

These metronomes move in and out of sync as they’re coupled and uncoupled. This is interesting because it’s a fundamentally nonlinear process. Sync provides a nice account of such things, and there’s a nifty interactive coupled pendulum demo here.

Mousetrap fission:

This is a physical analog of an infection model or the Bass diffusion model. It illustrates shifting loop dominance – initially, positive feedback dominates due to the chain reaction of balls tripping new traps, ejecting more balls. After a while, negative feedback takes over as the number of live traps is depleted, and the reaction slows.

## 4 thoughts on “Cool videos of dynamics”

1. I’d love to see the phase noise of the individual metronomes before and after the synchronization!

1. I tried to extract that from the audio track, but it turned out to be too noisy to see readily.

2. Great finds Tom! Now I have a visual way to describe shifting dominance to my kids.

I and the Sweeney children thank you.

Linda

1. Now that I think about it, fire is a nice example of shifting loop dominance. If you burn a sheet of paper, you start with a lot of fuel (analogous to untripped traps, potential customers, healthy people) and then start a positive feedback conversion process (burning -> heat -> ignition of adjacent paper). The cool thing is that you can vary the parameters of the system by varying the topology of the paper – long narrow strip, square, crumpled ball, etc. – and see how that changes the dynamics. Anything involving fire tends to be popular with kids, though there might be some unintended side effects.

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