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.
I’d love to see the phase noise of the individual metronomes before and after the synchronization!
I tried to extract that from the audio track, but it turned out to be too noisy to see readily.
Great finds Tom! Now I have a visual way to describe shifting dominance to my kids.
I and the Sweeney children thank you.
Linda
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.