Daily Archives: July 15, 2011

Science in Action

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There is no single scientific method, but over at Uncertain Principles, we can see an example of science getting done in a particular way.

First there’s an observation of a phenomenon, which runs contrary to another, similar phenomenon: Playground Physics: Roller Slide Mystery

The acceleration of an object sliding down a ramp, even with friction, should not depend on the mass of the object. And yet, I very clearly go faster than SteelyKid does, and while I don’t have the video to test it qualitatively, I’m pretty sure Kate’s rate of sliding falls between SteelyKid and me.

So, the question for you is: Why does that happen?

The question is raised, and discussion ensues. A promising hypothesis is offered in the comments (and not too long before I read the post, so I didn’t get a chance to think about it)

Chad fleshes out the concept behind the suggested model and presents the data:
Roller Slide Physics Explained

Lacking the time to go and get better data (which can be a proxy for those situations where circumstances dictate that you can’t get more data, we have a simulation based on the model that has been constructed.
Roller Slide Physics Simulated

The results certainly point to the model being plausible, and would allow for a more detailed experiment should someone wish to follow up on it. Not a bad representation of the scientific method. But I didn’t entitle this “Scientific Method in Action,” and for one reason:

I really ought to be doing other things, but this roller slide business kept nagging at me, and I eventually realized I could mock up a crude simulation of the results.

If you want to sum up what science all about — more than just the method — it would have to include the inquisitiveness of the people who practice it. Unsolved problems bug us, and it doesn’t even have to be your own problem. If you tell a scientist what you’re stuck on, it’s not unusual to get a response a little later on that starts off with “I was thinking about that problem — have you tried X?” When you’re stuck on your own problem, the distraction of someone else’s problem is very attractive.

See the Music

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Cool effect. Since this is not slow-motion, you might think it has to be basic aliasing: seeing a beat between the oscillations of the string and the frame-rate of a camera, often seen with wheels that look to be spinning slowly — or backward — on film. It’s not unlike the effect of a strobe light* that’s near the frequency of oscillation that make the motion seem slow or nonexistent, which sometimes happens with fluorescent (or rectified LED) lighting.

But it probably isn’t, or at least not in a simple way. When you strum a guitar the oscillations have a much longer wavelength. The fundamental mode is a standing wave where the string makes a half -wave (e.g. a 1m string has a wavelength of 2m), and there two nodes, one at either end. The next mode would have a node in the center and be a full wavelength. If the speed of sound is around 400 m/s, that gives a frequency of 200 Hz, or 400 Hz for the 2nd order mode. That’s about what we are hearing. The wavelengths shown in the video are much shorter, by more than an order of magnitude, and perhaps two. 20,000 Hz is way off. Plus the waveforms — you could get them by adding Fourier components, but that’s not going on here. This is a shutter effect, so it’s related to aliasing, but the sampling is happening as the exposure is scanned, i.e. each exposure is taking some time, and the exposure on the left side of the image does not represent the same time as the exposure on the right. This is called a rolling shutter and can have some pretty neat effects.

*Just bought a strobe. So I’ll be playing around with it.

Tea, Earl Grey, Hot

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Not quite there yet. But we have chocolate printing, and now 3D printing can make moving parts.

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3D printing is a form of additive manufacturing technology where a three dimensional object is created by laying down successive layers of material. 3D printers are generally faster, more affordable and easier to use than other additive manufacturing technologies.